Revisions to the Methodology for Deriving Ambient Water Quality
Criteria for the Protection of Human Health (2000)
[Federal Register: November 3, 2000 (Volume 65, Number 214)]
[Notices]
[Page 66443-66482]
From the Federal Register Online via GPO Access [wais.access.gpo.gov]
[DOCID:fr03no00-118]
[[Page 66443]]
-----------------------------------------------------------------------
Part III
Environmental Protection Agency
-----------------------------------------------------------------------
Revisions to the Methodology for Deriving Ambient Water Quality
Criteria for the Protection of Human Health (2000); Notice
[[Page 66444]]
-----------------------------------------------------------------------
ENVIRONMENTAL PROTECTION AGENCY
[WH-FRL-6893-6]
Revisions to the Methodology for Deriving Ambient Water Quality
Criteria for the Protection of Human Health (2000)
AGENCY: Environmental Protection Agency (EPA).
ACTION: Notice of Availability.
-----------------------------------------------------------------------
SUMMARY: EPA is announcing the availability of final revisions to the
Methodology for Deriving Ambient Water Quality Criteria for the
Protection of Human Health (2000) (hereafter ``2000 Human Health
Methodology'') published pursuant to section 304(a)(1) of the Clean
Water Act (CWA). The 2000 Human Health Methodology supersedes the
existing Guidelines and Methodology Used in the Preparation of Health
Effect Assessment Chapters of the Consent Decree Water Criteria
Documents, published by EPA in November 1980 (USEPA, 1980) (hereafter
``1980 AWQC National Guidelines'' or ``1980 Methodology''). Today's
Notice is intended to support the requirements of section 304(a)(1) of
the CWA that EPA periodically revise criteria for water quality to
accurately reflect the latest scientific knowledge on the kind and
extent of all identifiable effects on health and welfare that may be
expected from the presence of pollutants in any body of water,
including ground water. These revisions are prompted by the many
significant scientific advances that have occurred during the past 20
years in such key areas as cancer and noncancer risk assessments,
exposure assessments, and bioaccumulation assessments. These revisions
are not regulations and do not impose legally-binding requirements on
EPA, States, Tribes, or the public.
DATES: Technical Support Documents (TSD) on exposure assessment
guidance and bioaccumulation guidance applicable to the 2000 Human
Health Methodology are expected to become available early in calendar
year 2001.
ADDRESSES: The 2000 Human Health Methodology is published in the
document entitled, Methodology for Deriving Ambient Water Quality
Criteria for the Protection of Human Health (2000). This document is
available on the EPA website at www.epa.gov/OST/humanhealth. A
Technical Support Document (TSD) volume on risk assessments applicable
to the 2000 Human Health Methodology is also available from the
website. Materials in the public docket will be available for public
inspection and copying during normal business hours at the Office of
Water Docket, 401 M St., SW, Washington, DC 20460 by appointment only.
Appointments may be made by calling (202) 260-3027 and requesting item
W-97-20. A reasonable fee will be charged for photocopies.
FOR FURTHER INFORMATION CONTACT: Denis R. Borum, Health and Ecological
Criteria Division (4304), U.S. EPA, Ariel Rios Building, 1200
Pennsylvania Avenue, NW, Washington, DC 20460; (202) 260-8996;
borum.denis@epa.gov.
SUPPLEMENTARY INFORMATION: This Supplementary Information Section is
organized as follows:
I. Background Information
A. What are human health ambient water quality criteria?
B. How is the Human Health Methodology used?
C. Why was the Methodology revised?
D. What specific scientific advances have occurred since 1980?
E. What process did EPA follow in revising the Methodology?
F. What are the major revisions to the Methodology?
G. How will EPA use the Human Health Methodology?
II. Implementation Issues
A. How does EPA use its recommended 304(a) water quality
criteria?
B. What water quality criteria must a State or authorized Tribe
adopt into its water quality standards?
C. May States and authorized Tribes adopt water quality criteria
based on local conditions?
D. What cancer risk level should States and authorized Tribes
use when establishing water quality criteria?
E. How does the Review and Approval of State and Tribal Water
Quality Standards rule affect water quality criteria adopted by
States and authorized Tribes?
F. While EPA is re-evaluating a 304(a) criterion, what criterion
is in effect?
G. What design stream flow should be used to implement human
health criteria?
H. What is the relationship between the Agency's recommended
Section 304(a) water quality criteria and drinking water standards?
I. How are health risks to children considered in the
Methodology?
III. Summary of Comments Received on the 1998 Draft Methodology
Revisions and EPA's Responses
A. Implementation
1. Application of Human Health Criteria Within Mixing Zones
2. Application of Human Health Water Quality Criteria to Marine
Waters
3. Cancer Risk Range
4. Coordinating the Human Health Methodology With Other EPA
Programs
5. Designated Uses
6. Developing National 304(a) Criteria
7. Developing Organoleptic Criteria
8. Establishing EPA's Most Recent Federally Recommended Water
Quality Criteria
9. Flows
10. Implementation on a Waterbody Basis
11. Proposed Chemical List
12. Publishing Existing 304(a) Criteria Information
13. Revising Existing 304(a) Criteria
14. State Evaluation of Data Supporting Criteria
15. Streamlined Approach to Developing Criteria Documents
16. Treaty Rights and Trust Obligations/Government-to-Government
Relations
B. General Policy
1. AWQC Derivation Equation Errors
2. Chronic Human Health Effects Assumption
3. Protectiveness of the Methodology
4. Setting Criteria to Protect Both Fish and Drinking Water
Versus Fish Only
5. Setting Criteria to Protect Against Multiple Exposures From
Multiple Chemicals
6. Uncertainty with the Derivation of 304(a) Criteria
7. Toxicity Equivalency Factors (TEFs) for Dioxin-like Compounds
C. Cancer
1. Acceptable Risk Level for Carcinogens
2. ED10 (central estimate) versus LED10 (lower bound on dose)
3. Group C Contaminants
4. Guidance on Carcinogen Risk Assessment
5. Hexachlorobutadiene (HCBD)
6. Integration of Analyses for Cancer and Noncancer Effects
7. Margin of Exposure (MOE) Analysis
8. MOE Approach to Applying Uncertainty Factors (UFs)
9. MOE and MOP
10. Oral Scaling Factor for Dose Adjustment
11. Toxic Endpoints
12. Weight-of-Evidence Narrative and Classification System
D. Noncancer
1. Benchmark Dose Methodology
2. Categorical Regression
3. Integrated Approach
4. Integrated Risk Information System (IRIS)
5. NOAEL/LOAEL Approach
6. Nonthreshold Approach for Noncarcinogens
7. RfD Range
8. Severity of Effects
9. Stochastic Modeling
10. Synergistic Effects
11. Target Population Adjustments
12. Uncertainty and Modifying Factors
13. Use of Less-Than-90-Day Studies in Determining an RfD
E. Exposure Assessment
Default Intakes
1. Assumption That All of the Drinking Water Consumed Is
Contaminated at the Criteria Level
2. Assumption That All Fish Consumed Is Contaminated at the
Criteria Level and All Fish May Come from One Waterbody
3. Body Weight Assumptions
4. Combining Consumption Intakes and Body Weights
5. Combining Fish Intake and Body Weights
[[Page 66445]]
6. Default Drinking Water Intake Rates
7. Default Fish Intake Rates
8. Effect of Cooking on the Contaminant Concentration
9. Inclusion of Marine Species in the Default Rate
10. Precision of the Drinking Water Parameter
11. Redesignation of Salmon as a Marine Species
12. Studies on Sportfishers and Subsistence Fishers
13. USDA Continuing Survey of Food Intake by Individuals (CSFII)
14. Use of Uncooked or As Consumed Fish Weight for Default
Intake Rates
Relative Source Contribution (RSC)
15. Default Percentages and RSC Floor of 20% and Ceiling of 80%
16. Duplication of Fish Intake Assumptions
17. Exposure Route Differences
18. Need for an RSC Factor/Considering Multiple Routes of
Exposure
19. Use of RSC With Carcinogenic Effects Based on Linear Low-
Dose Extrapolation
20. Use of Subtraction or Percentage Methods in RSC
Apportionment
F. Bioaccumulation
1. Use of Bioaccumulation Factors (BAFs) in General
2. Guidance for Deriving Field Bioaccumulation Factors (BAFs)
3. Use of Biota-Sediment Accumulation Factors (BSAFs)
4. Dissolved Organic Carbon (DOC) and Particulate Orgain Carbon
(POC)
5. Fish Lipid Content
6. Use of Food Chain Multipliers (FCMs)
7. Fish Tissue Criteria
G. Literature Cited
I. Background Information
A. What are Human Health Ambient Water Quality Criteria?
Human health ambient water quality criteria (AWQC) are numeric
values for pollutant concentrations in ambient waters considered to be
protective of human health. The criteria are developed under section
304(a) of the Clean Water Act (CWA) and are based solely on data and
scientific judgments on the relationship between pollutant
concentrations and environmental and human health effects. Protective
assumptions are made regarding the potential human exposure intakes.
These criteria do not reflect consideration of economic impacts or the
technological feasibility of meeting the chemical concentrations in
ambient water. Section 304(a)(1) of the CWA requires EPA to develop and
publish, and from time to time revise, criteria for water quality
accurately reflecting the latest scientific knowledge. The criteria are
used by States and authorized Tribes to establish water quality
standards and ultimately provide a basis for controlling discharges or
releases of pollutants. The criteria also provide guidance to EPA when
promulgating Federal regulations under CWA Section 303(c) when such
actions are necessary.
In 1980, we published AWQC (i.e., Section 304(a) criteria) for 64
pollutants/pollutant classes and provided a methodology for deriving
the criteria. The 1980 AWQC National Guidelines for developing human
health AWQC addressed three types of endpoints: noncancer, cancer and
organoleptic (taste and odor) effects. Criteria for the protection
against noncancer and cancer effects were estimated by using risk
assessment-based procedures, including extrapolation from animal
toxicity or human epidemiological studies. Basic human exposure
assumptions were applied to the criterion equation. When using cancer
as the critical risk assessment endpoint, which was assumed not to have
a threshold, the AWQC were presented as concentrations associated with
specified incremental lifetime risk levels. When using noncancer
effects as the critical endpoint, the AWQC reflected an assessment of a
``no-effect'' level, based on an assumption of a threshold for
noncancer effects.
B. How Is the Human Health Methodology Used?
The Methodology is used by EPA to derive or revise its section
304(a) criteria. It provides the detailed means for developing the
water quality criteria, including systematic procedures for evaluating
cancer risk, noncancer health effects, human exposure, and
bioaccumulation potential in fish. This Methodology is also guidance
for States and authorized Tribes to help them establish water quality
criteria to protect human health. States and authorized Tribes must
develop water quality standards that include designated uses and water
quality criteria necessary to support those uses.
C. Why Was the Methodology Revised?
EPA periodically revises water quality criteria to ensure that they
reflect the latest scientific knowledge on the kind and extent of all
identifiable effects on health and welfare that may be expected from
the presence of pollutants in any body of water, including ground
water. Since 1980, many significant scientific advances have occurred
which prompt revisions to the Methodology. Specifically, advances in
such key areas as cancer and noncancer risk assessments, exposure
assessments, and bioaccumulation make the revisions appropriate at this
time. We therefore updated the Methodology to provide States and
authorized Tribes with the most current procedures to reflect these
changes in risk and exposure assessment. States and authorized Tribes
can use the Methodology to modify their water quality criteria, as
appropriate, to ensure that their criteria are protective of designated
uses.
Another reason for these revisions is the need to address
differences in the risk assessment and risk management approaches used
by the EPA Office of Water for the derivation of AWQC--under the
authority of the CWA--and Maximum Contaminant Level Goals (MCLGs)--
under the authority of the Safe Drinking Water Act (SDWA). Three
notable differences in these revisions include the treatment of
chemicals designated as Group C possible human carcinogens under the
1986 Guidelines for Carcinogen Risk Assessment (USEPA, 1986a), the
consideration of non-water sources of exposure when setting an AWQC or
MCLG for a noncarcinogen, and cancer risk ranges.
1. Group C Chemicals. Chemicals classified as Group C--i.e.,
possible human carcinogens'under the existing (1986) EPA cancer
classification scheme have been typically classified as such for any of
the following reasons.
(1) Carcinogenicity has been documented in only one test species
and/or only one cancer bioassay, and the results do not meet the
requirements of ``sufficient evidence.''
(2) Tumor response is of marginal statistical significance due to
inadequate design or reporting.
(3) An agent causes benign, but not malignant, tumors and no
response in a variety of short-term tests for mutagenicity.
(4) There are responses of marginal statistical significance in a
tissue known to have a high or variable background rate.
The 1986 Guidelines for Carcinogen Risk Assessment (hereafter
``1986 cancer guidelines'') specifically recognized the need for
flexibility with respect to quantifying the risk of Group C agents
(USEPA, 1986a). The 1986 cancer guidelines noted that agents judged to
be in Group C, possible human carcinogens, may generally be regarded as
suitable for quantitative risk assessment, but that case-by-case
judgments may be made for them.
EPA has historically treated Group C chemicals differently under
the CWA and the SDWA. It is important to note that the 1980 AWQC
National Guidelines for setting AWQC under the CWA predated EPA's
carcinogen classification system, which was proposed in 1984 and
finalized in 1986 (USEPA, 1984, 1986a). The 1980 AWQC National
Guidelines did not explicitly
[[Page 66446]]
differentiate among agents with respect to the weight of evidence for
characterizing them as likely to be carcinogenic to humans. For all
pollutants judged as having adequate data for quantifying carcinogenic
risk--including those now classified as Group C--AWQC were derived
based on cancer incidence data. In the November 1980 Federal Register
Notice, we emphasized that the AWQC for carcinogens should state that
the recommended concentration for maximum protection of human health is
zero. At the same time, the criteria published for specific carcinogens
presented water concentrations for these pollutants corresponding to
individual lifetime cancer risk levels in the range of 10-7
to 10-5 (ranging from one case in a population of ten
million to one case in a population of one hundred thousand).
In the development of national primary drinking water regulations
under the SDWA, EPA is required to promulgate a health-based MCLG for
each contaminant. Our policy has been to set the MCLG at zero for
chemicals with strong evidence of carcinogenicity associated with
exposure from water. For chemicals with limited evidence of
carcinogenicity, including many Group C agents, the MCLG was usually
obtained using a Reference Dose (RfD) based on its noncancer effects
with the application of an additional factor of 1 to 10. If valid
noncancer data for a Group C agent were not available to establish an
RfD, but adequate data were available to quantify the cancer risk, then
the MCLG was based upon a nominal lifetime excess cancer risk
calculation in the range of 10-6 to 10-5 (ranging
from one case in a population of one million to one case in a
population of one hundred thousand). Even in those cases where the RfD
approach has been used for the derivation of the MCLG for a Group C
agent, the drinking water concentrations associated with excess cancer
risks in the range of 10-6 to 10-5 were also
provided for comparison.
It should also be noted that in actions taken under the Federal
Insecticide, Fungicide, and Rodenticide Act (FIFRA), EPA's pesticides
program has applied both of these methods for addressing Group C
chemicals and finds both methods (quantified ``C's'' and nonquantified
``C's'') applicable on a case-by-case basis. Unlike the drinking water
program, however, the pesticides program does not add an extra
uncertainty factor to account for potential carcinogenicity when using
the RfD approach.
The EPA is in the process of revising its cancer guidelines,
including its descriptions of human carcinogenic potential. Once final
guidelines are published, they will be the basis for assessment under
this Methodology. In the meanwhile, the 1986 cancer guidelines are used
and extended with principles discussed in EPA's 1999 Guidelines for
Carcinogen Risk Assessment--Review Draft (hereafter ``1999 draft
revised cancer guidelines''). These principles arise from scientific
discoveries about cancer made in the last 15 years and from EPA policy
of recent years supporting full characterization of hazard and risk
both for the general population and potentially sensitive groups such
as children. These principles are incorporated in recent and ongoing
assessments such as the reassessment of dioxin, consistent with the
1986 cancer guidelines. Until final guidelines are published,
information is presented to describe risk under both the 1986
guidelines and the 1999 draft revisions. To bring in new science and
characterization principles, draft revisions have weight-of-evidence
narratives for hazard characterization that use consistent descriptive
terms (USEPA, 1999a). In order to provide some measure of consistency
in an otherwise free-form, narrative characterization, standard
descriptors are utilized as part of the hazard narrative to express the
conclusion regarding the weight of evidence for carcinogenic hazard
potential. There are five standard hazard descriptors: ``carcinogenic
to humans'', ``likely to be carcinogenic to humans'', ``suggestive
evidence of carcinogenicity but not sufficient to assess human
carcinogenic potential'', ``data are inadequate for an assessment of
human carcinogenic potential'', and ``not likely to be carcinogenic to
humans.'' Each standard descriptor may be applicable to a wide variety
of data sets and weights of evidence and are presented only in the
context of a weight-of-evidence narrative. Furthermore, more than one
conclusion may be reached for a pollutant. For instance, using a
descriptor in context, a narrative could say that a pollutant is likely
to be carcinogenic by inhalation exposure and not likely to be
carcinogenic by oral exposure.
In the 2000 Human Health Methodology, we quantify those pollutants
considered ``carcinogenic to humans'' or ``likely to be carcinogenic to
humans.'' In practice, even though the terminology of the 1999 draft
revised cancer guidelines differs, this is the approach currently used
by the EPA pesticides program.
2. Consideration of Non-water Sources of Exposure. The 1980 AWQC
National Guidelines for setting AWQC recommended that contributions
from non-water sources, namely air and non-fish dietary intake, be
subtracted from the Acceptable Daily Intake (ADI), thus reducing the
amount of the ADI ``available'' for water-related sources of intake. In
practice, however, when calculating human health criteria, those other
exposures were generally not considered because reliable data on those
exposure pathways were not available. Consequently, the AWQC were
usually derived such that drinking water and fish ingestion accounted
for the entire ADI (now called RfD).
Through the mid-1980s, the drinking water program generally used a
similar ``subtraction'' method in the derivation of MCLGs, albeit
inconsistently. More recently, the drinking water program has used a
``percentage'' method in the derivation of MCLGs for noncarcinogens. In
this approach, the percentage of total exposure typically accounted for
by drinking water is applied to the RfD to determine the maximum amount
of the RfD apportioned to drinking water reflected by the MCLG value.
This percentage is called the relative source contribution (RSC). In
using this percentage procedure, the drinking water program also
applies a ceiling of 80 percent of the RfD and a floor of 20 percent of
the RfD. That is, the MCLG cannot account for more than 80 percent of
the RfD, nor less than 20 percent of the RfD.
The drinking water program usually takes a conservative approach to
public health by applying an RSC factor of 20 percent to the RfD when
adequate exposure data do not exist, assuming that the major portion
(80 percent) of the total exposure comes from other sources, such as
diet.
The 2000 Human Health Methodology includes guidance for routine
consideration of non-water sources of exposure [both ingestion
exposures (e.g., food) and exposures other than the oral route (e.g.,
inhalation)] via an approach called the Exposure Decision Tree. RSC
estimates will be made by EPA using this approach, which allows for use
of either subtraction or percentage methods, depending on chemical-
specific circumstances, within the 20 to 80 percent range described
above.
3. Cancer Risk Ranges. In addition to the different risk assessment
approaches discussed above for deriving AWQC and MCLGs for Group C
agents, there have been different risk management approaches by the
drinking water and
[[Page 66447]]
ambient surface water programs on using lifetime excess risk values
when setting health-based criteria for carcinogens. The surface water
program historically derived AWQC for carcinogens that generally
corresponded to lifetime excess cancer risk levels of 10-7
to 10-5. The drinking water program has set MCLGs for Group
C agents based on a slightly less stringent risk range of
10-6 to 10-5, while MCLGs for chemicals with
strong evidence of carcinogenicity (that is, classified as Group A
(known) or B (probable) human carcinogen) are set at zero. The drinking
water program is now following the 1999 draft revised cancer guidelines
to determine the type of low-dose extrapolation based on mode of
action.
It is also important to note that under the drinking water program,
for those substances having an MCLG of zero, enforceable Maximum
Contaminant Levels (MCLs) have generally been promulgated to correspond
with cancer risk levels ranging from 10-6 to
10-4. Unlike AWQC and MCLGs which are strictly health-based
criteria, MCLs are developed with consideration given to the costs and
technological feasibility of reducing contaminant levels in water to
meet those standards.
The 2000 Human Health Methodology states that EPA will publish its
national 304(a) water quality criteria at a 10-6 risk level,
which we consider to be appropriate for the general population. Again,
consistent with the 1999 draft revised cancer guidelines, there are no
more alphanumeric categories. We will only quantify those considered
``carcinogenic to humans'' or ``likely to be carcinogenic to humans.''
We are increasing the degree of consistency between the drinking water
and ambient water programs, given somewhat different requirements of
the CWA and SDWA. We will use the same hazard characterizations of
dose-response.
B. What Specific Scientific Advances Have Occurred Since 1980?
Since 1980, EPA risk assessment practices have evolved
significantly in all of the major Methodology areas: cancer and
noncancer risk assessments; exposure assessments; and bioaccumulation.
EPA first published guidelines on cancer risk assessment in 1986. EPA
published Proposed Guidelines for Carcinogen Risk Assessment in 1996
(hereafter ``1996 proposed cancer guidelines''; USEPA, 1996a). These
were recently revised following review by the Agency's Science Advisory
Board (SAB) and receipt of their comments in May 1999. The most recent
document is the July 1999 draft revised cancer guidelines (USEPA,
1999a). The 1999 draft revised cancer guidelines discuss the use of
mode of action (MOA) information to support both the identification of
carcinogens and the selection of procedures to characterize risk at
low, environmentally relevant exposure levels. They also address the
development of new procedures to quantify cancer risks at low doses to
replace the current default use of the linearized multistage (LMS)
model. In noncancer risk assessment, we are moving toward the use of
the benchmark dose (BMD) and other dose-response methodologies in place
of the traditional NOAEL approach to estimate an RfD concentration or
other point of departure (POD) divided by an uncertainty factor (UF).
In addition, several risk assessment guidelines have been published.
For example, in 1986 EPA published Guidelines for Mutagenicity Risk
Assessment (USEPA, 1986b). In 1991, EPA published the Guidelines for
Developmental Toxicity Risk Assessment (USEPA, 1991a), and in 1996, it
published the Guidelines for Reproductive Toxicity Risk Assessment
(USEPA, 1996b). In 1998, EPA also published the Guidelines for
Neurotoxicity Risk Assessment (USEPA, 1998a). In May 1999, EPA
published the Draft Guidance for Conducting Health Risk Assessment of
Chemical Mixtures (USEPA, 1999b). In addition, the Agency is developing
a framework for cumulative risk assessment, and the Office of Pesticide
Programs has developed draft guidance for assessing cumulative risk of
common mechanism pesticides and other substances.
In 1986, EPA made available to the public the Integrated Risk
Information System (IRIS). IRIS is a database that contains risk
information on the cancer and noncancer effects of chemicals. The IRIS
assessments represent EPA scientific consensus positions across the
Agency's program offices and regional offices.
In exposure analysis, several new studies have addressed water
consumption and fish tissue consumption. These exposure studies provide
a more current and comprehensive description of national, regional and
special population consumption patterns that we reflected in the 1998
Draft Water Quality Criteria Methodology: Human Health (hereafter
``1998 draft Methodology revisions''; USEPA, 1998c). In addition, more
formalized procedures are available to account for human exposure to
multiple sources when setting health goals such as AWQC that have
previously addressed only one exposure source. The Exposure Factors
Handbook was updated in 1997 (USEPA, 1997a). In 1992, we published the
revised Guidelines for Exposure Assessment (USEPA, 1992a), which
describe general concepts of exposure assessment, including definitions
and associated intake rate parameters, and provide guidance on planning
and conducting an exposure assessment. In 1986, the Agency published
the Total Exposure Assessment Methodology (TEAM) Study: Summary and
Analysis, Volume I, Final Report (USEPA, 1986c), which presents a
process for conducting comprehensive evaluation of human exposures. The
Agency has recently developed a revised relative source contribution
(RSC) policy for assessing total human exposure to a contaminant and
apportioning the RfD among the media of concern for use in deriving or
revising AWQC. In 1997, we developed Guiding Principles for Monte Carlo
Analysis (USEPA, 1997b). Also in 1997, we published the Policy for Use
of Probabilistic Analysis in Risk Assessment (USEPA, 1997c; see http://
www.epa.gov/ncea/mcpolicy.htm). The Monte Carlo guidance document can
be applied to exposure assessments and risk assessments. The Agency has
moved toward the use of a bioaccumulation factor (BAF) to reflect the
uptake of a contaminant from all sources (e.g., ingestion, sediment) by
fish and shellfish, rather than just from the water column as reflected
by the use of a bioconcentration factor (BCF) in the 1980 Methodology.
We have developed detailed procedures and guidelines for estimating BAF
values for use in deriving or revising AWQC.
C. What Process Did EPA Follow in Revising the Methodology?
We began by developing (along with other Federal agencies, State
health organizations, Canadian health agencies, academies,
environmental and industry groups, and consulting organizations) an
issues paper that described the 1980 Methodology, discussed areas that
needed strengthening, and recommended revisions. The paper was
distributed for review and comment and was examined at a national
workshop, where more than 100 participants discussed critical issues.
Based on individual expertise, attendees were assigned to specific
technical workgroups. The workgroups' topics included cancer risk,
noncancer risk, exposure, microbiology, minimum data and
bioaccumulation in fish.
A summary document based on the workshop recommendations was
submitted for review and comment by the EPA SAB. Once final comments
and
[[Page 66448]]
revisions were received from the SAB, the recommendations were again
reviewed at a meeting of the Federal-State Toxicology and Risk Analysis
Committee, where state representatives presented their opinions on the
preliminary draft recommendations. (A more detailed chronology of this
process was provided with the 1998 draft Methodology revisions.)
EPA subsequently developed the 1998 draft Methodology revisions
(USEPA, 1998c) and the Ambient Water Quality Criteria Derivation
Methodology Human Health Technical Support Document (TSD) (USEPA,
1998d) that provides greater detail on the Methodology guidance--
including case study examples, data tables, and other supporting
information. These were published in the Federal Register in August
1998. A four-month public comment period followed. In May of 1999, a
fifteen-member independent peer review workshop was held, and a public
stakeholder meeting followed. The 2000 Human Health Methodology
reflects, in part, the input received from the public and peer review
experts, in addition to more recent scientific information and science
policies since the 1998 draft publication.
F. What Are the Major Revisions to the Methodology?
The major revisions are in four assessment areas: Noncancer,
cancer, exposure and bioaccumulation. Equations have been developed for
deriving AWQC, which include parameters relevant to those four
assessment areas. These parameters are derived from scientific
analysis, science policy and risk management decisions.
For noncarcinogens, the process for deriving a level of exposure
considered to be without appreciable risk of effect--known as the
Reference Dose (RfD) value--has evolved over time.
EPA has developed guidance on assessing noncarcinogenic
effects of chemicals and for the RfD derivation.
The Methodology revisions recommend consideration of other
issues related to the RfD process including integrating reproductive/
developmental, immunotoxicity, and neurotoxicity data into the
calculation.
EPA is recommending the use of quantitative dose-response
modeling for the derivation of RfDs.
EPA has provided additional guidance (in its Risk
Assessment TSD) to allow States and authorized Tribes greater
flexibility in conducting their own risk assessments.
For carcinogen (cancer) risk assessment, more sophisticated methods
for determining the likely mechanism that causes human carcinogenicity
are being recommended, as well as consideration of all biological
information (rather than just tumor findings) and full risk
characterization for the general population as well as sensitive groups
such as children.
Changes in the area of exposure assessment include the following.
States and authorized Tribes are encouraged to use local
studies on fish consumption that better reflect local intake patterns
and choices.
EPA will recommend default fish consumption values for the
general population, recreational fishers and subsistence fishers.
A factor to account for other sources of exposure, such as
food and air, is included when deriving AWQC for noncarcinogens and for
carcinogens based on a nonlinear low-dose extrapolation (i.e., water
and fish consumption are not the only exposures considered).
The 2000 Human Health Methodology places greater emphasis on the
use of BAFs compared to the 1980 Methodology for estimating potential
human exposure to contaminants via the consumption of contaminated fish
and shellfish.
BAFs reflect the accumulation of chemicals by aquatic
organisms from all surrounding media (water, food, sediment). Compared
with BCFs, which reflect chemical accumulation by aquatic organisms
from water only, BAFs are considered to be better predictors of
chemical accumulation by fish and shellfish for chemicals where
exposure from food and sediment is important (e.g., highly persistent,
hydrophobic chemicals).
EPA gives preference to the use of high quality field data
over laboratory or model-derived estimates of BAFs, since field data
best reflect factors that can affect the extent of bioaccumlation
(e.g., chemical metabolism, food web structure).
G. How Will EPA Use the Human Health Methodology?
Our future role in developing AWQC for the protection of human
health will include the following.
Further refinement of the Methodology as the science and
EPA's science policies evolve;
Development of revised AWQC for pollutants of high
priority and national importance (including, but not limited to
chemicals that bioaccumulate, such as PCBs, dioxin, and mercury); and
Development or revision of AWQC for some additional
priority pollutants.
We plan to fully update the most environmentally important criteria
developed in 1980 (or those updated as part of the 1992 National Toxics
Rule (NTR)). Partial updates of substantially more criteria may be
warranted. We encourage States and authorized Tribes to use the 2000
Human Health Methodology to develop or revise AWQC to reflect local
conditions. EPA believes that AWQC inherently require several risk
management decisions that are, in many cases, better made at the State
or Tribal level (e.g., selection of specific fish consumption rates or
target risk levels). We will continue to develop and update necessary
toxicology and exposure data needed for the derivation of AWQC that may
not be practical for the States or Tribes to obtain. More information
on implementation issues and the effect of the 2000 Human Health
Methodology on States and authorized Tribes is discussed below.
II. Implementation Issues
Water quality standards consist of designated uses, water quality
criteria to protect those uses, a policy for antidegradation, and
general policies for application and implementation. As part of the
water quality standards triennial review process defined in section
303(c)(1) of the CWA, States and authorized Tribes are responsible for
maintaining and revising water quality standards. Section 303(c)(1)
requires States and authorized Tribes to review, and modify if
appropriate, their water quality standards at least once every three
years.
A. How Does EPA Use Its Recommended 304(a) Water Quality Criteria?
EPA's recommended 304(a) water quality criteria form the basis for
Agency decisions, both regulatory and nonregulatory, until superseded
by EPA publication of new or revised 304(a) water quality criteria. For
example, these criteria are used in the following ways: (1) As guidance
to States and authorized Tribes in adopting water quality standards;
(2) as guidance to EPA in promulgating Federal water quality standards;
(3) in establishing National Pollutant Discharge Elimination System
(NPDES) water quality-based permit limits, where the criteria have been
adopted by a State or authorized Tribe or promulgated by EPA; and (4)
for all other purposes of Section 304(a) criteria under the Act. It is
important to emphasize again two distinct purposes which are served by
the 304(a) criteria. The first is as guidance to the States and Tribes
in the development and adoption of water quality criteria which will
protect designated uses. The second is as the basis for promulgation of
Federal water
[[Page 66449]]
quality standards for States or authorized Tribes when such action is
necessary.
B. What Water Quality Criteria Must a State or Authorized Tribe Adopt
Into Its Water Quality Standards?
States and authorized Tribes must adopt water quality criteria that
protect designated uses. Such criteria must be based on sound
scientific rationale and must contain sufficient parameters or
components to protect the designated uses. Criteria may be expressed in
either narrative or numeric form. States and authorized Tribes have
four options when adopting water quality criteria for which EPA has
published 304(a) criteria. They can establish numerical values based on
304(a) criteria, 304(a) criteria modified to reflect site-specific
conditions, other scientifically defensible methods, or establish
narrative criteria where numeric criteria cannot be determined. (See 40
CFR 131.11.)
EPA's recommended 304(a) water quality criteria for States and
authorized Tribes to use as guidance in adopting water quality
standards consistent with Section 303(c) of the Act and the
implementing Federal regulations at 40 CFR part 131 are contained in
EPA's last compilation of National Recommended Water Quality Criteria
(USEPA, 1998e) (corrected in USEPA, 1999c). In the future, we will be
publishing new and revised 304(a) water quality criteria based upon the
2000 Human Health Methodology for pollutants of high priority and
national importance. Because the revision of existing 304(a) human
health criteria to reflect the 2000 Human Health Methodology will take
time, EPA encourages States and authorized Tribes to make appropriate
changes to their existing numerical, pollutant-specific criteria in
their water quality standards to reflect this new Methodology prior to
publication of a revised 304(a) criteria where they determine that such
actions are necessary. For example, a pollutant of concern in a
particular State may not be a high priority on the national level and
revision of the national 304(a) criteria may not occur for several
years. In this case, the State or a group of States, might choose to
use this new Methodology to revise their water quality standards prior
to EPA publication of a revised 304(a) criteria for that pollutant. EPA
will recognize criteria that are revised pursuant to the 2000 Human
Health Methodology as scientifically defensible and promptly approve
such revised criteria as enforceable elements of State or Tribal water
quality standards.
Once a new or revised 304(a) criteria reflecting this new
Methodology is published, EPA expects States and authorized Tribes to
reassess their water quality standards and, where necessary, establish
new or revised water quality criteria consistent with one of the four
options described above. Because of the critical role that human health
ambient water quality criteria play in protecting human health, EPA
will work with States and authorized Tribes to revise existing water
quality standards promptly following EPA publication of revised section
304(a) criteria.
C. May States and Authorized Tribes Adopt Water Quality Criteria Based
on Local Conditions?
In keeping with their primary responsibility in establishing water
quality standards, we encourage States and authorized Tribes to develop
and adopt water quality criteria to reflect local and regional
conditions. States and authorized Tribes will have access to EPA
regional, laboratory, and headquarters staff when help is needed to
interpret today's Human Health Methodology and to make critical risk
assessment decisions. For the purpose of deriving criteria based on the
2000 Human Health Methodology, EPA is publishing default values for
risk level, fish intake, drinking water intake, and body weight.
Default BAF values and RSC factor values will be published as chemical-
specific criteria are developed or revised. (Other RSC estimates will
be made when data are adequate to make them.) We believe these default
values result in water quality criteria protective of the general
population, and we will use these values when deriving 304(a) criteria.
States and authorized Tribes may use other values more representative
of local conditions if data have been collected supporting the
alternative values. However, when establishing a numerical value based
on a 304(a) criterion modified to reflect site-specific conditions, or
water quality criteria based on other scientifically defensible
methods, we strongly caution States and authorized Tribes not to
selectively apply data in order to ensure water quality criteria less
stringent than EPA's 304(a) criteria. Such an approach would
inaccurately characterize risk.
D. What Cancer Risk Level Should States and Authorized Tribes Use When
Establishing Water Quality Criteria?
In deriving 304(a) criteria based on the 2000 Human Health
Methodology or when promulgating Federal water quality standards under
section 303(c) of the CWA, EPA intends to use a 10-61 cancer
risk level, which we believe reflects an appropriate target risk level
for the general population. EPA acknowledges that at any given cancer
risk level for the general population, those segments of the population
that are more highly exposed face a higher relative risk. For example,
if fish are contaminated at a level allowed by criteria derived on the
basis of a risk level of 10-6, individuals consuming up to
10 times the assumed fish consumption rate would still be protected at
a 10-5 risk level. States and authorized Tribes have the
flexibility to adopt water quality criteria that result in a risk level
higher than 10-6, up to the 10-5 level. EPA
recommends adoption of such criteria if the State or Tribe has
identified the most highly exposed subpopulation within the State or
Tribe, has demonstrated that the chosen cancer risk level is protective
of the most highly exposed subpopulations, and has completed all
necessary public participation. EPA notes that special scientific
circumstances and assessment of natural contaminants may lead to
numbers outside the 10-6 to 10-5 risk range. (For
additional discussion on this issue, including restrictions on
selection of a cancer risk level, refer to the response on the comment
for cancer risk ranges summarized in Section III of this Notice,
below.)
E. How Does the Review and Approval of State and Tribal Water Quality
Standards Rule Affect Water Quality Criteria Adopted by States and
Authorized Tribes?
Consistent with the Review and Approval of State and Tribal Water
Quality Standards rule revision (USEPA, 2000a), water quality criteria
adopted into law or regulation by States and authorized Tribes prior to
May 30, 2000, are in effect for CWA purposes unless superseded by
replacement Federal water quality standards (see, for example, the
National Toxics Rule, 40 CFR 131.35; Water Quality Standards for Idaho,
40 CFR 131.35). Water quality criteria adopted into law or regulation
by States and authorized Tribes after May 30, 2000, are in effect for
CWA purposes only after EPA approval of any new or revised water
quality standards.
F. While EPA is Re-Evaluating a 304(a) Criterion, What Criterion Is in
Effect?
Until such time as EPA reevaluates the 304(a) criteria, subjects
the criteria to appropriate peer review, and subsequently publishes
revised 304(a) criteria, the existing 304(a) criteria remain in effect
for the purposes of EPA review of State and Tribal water quality
standards under section 303(c). Where EPA has not published a revision
of a
[[Page 66450]]
304(a) criteria reflecting the 2000 Human Health Methodology, EPA will
not require the revision of State water quality standards to reflect
this new Methodology. As noted above, however, EPA will assist those
States or Tribes that choose to use the new Methodology to revise their
existing water quality standards prior to publication of a revised
criteria under section 304(a).
G. What Design Stream Flow Should Be Used to Implement Human Health
Criteria?
Human health criteria represent ambient pollutant concentrations
that are acceptable based on a lifetime (70 years) of exposure.
Accordingly, discharges of pollutants should be regulated such that
criteria will not be exceeded under stream conditions that represent
long-term average conditions. Current EPA guidance recommends the use
of the long-term harmonic mean flow to implement criteria for
carcinogens and the 30Q5 flow to implement criteria for noncarcinogens
(USEPA, 1991b). The harmonic mean flow is the sum of the reciprocals of
individual flow measurements divided into the total number of
individual flow measurements, and the 30Q5 flow is defined by the
lowest 30-day average that has an expected return frequency of once
every five years. With today's Human Health Methodology, EPA is
revising its guidance to recommend harmonic mean flow be used to
implement both carcinogen and noncarcinogen human health criteria.
Harmonic mean flow should be used to implement human health criteria
because, by and large, human health criteria are designed to protect an
individual over a lifetime of exposure. As stated in the 1998 draft
Methodology revisions, we are not recommending the development of
additional water quality criteria similar to the drinking water health
advisories that focus on acute or short-term effects. These are not
seen as routinely having a meaningful role in the water quality
criteria and standards program because the chronic health effects
associated with chemical contaminants are usually the most sensitive
health endpoint. Human health criteria based on cancer potencies and
risk levels are based on models that extrapolate animal data to a human
lifetime. Similarly, a human noncancer criterion is based on an RfD,
which is an acceptable daily exposure over a lifetime. Therefore, we
have attempted to match the longest stream flow averaging period (using
harmonic mean) with the criterion which is protective over a human
lifetime.
In rare instances where a human health criterion or value is based
on a short-term toxicological effect (i.e., the critical effect upon
which the criterion/value is based is significantly less than lifetime
and may be an acute effect), the design flow should be adjusted
accordingly. This does not pertain to RfDs in which a short-term study
has been used as the RfD basis and an uncertainty factor has been used
to account for less than lifetime study results; that is, the short-
term study has been used to estimate a lifetime RfD value. This
pertains only to those situations where the critical effect is a short-
term effect (and where no additional uncertainty factor has been used
to account for less than lifetime exposure). A good example of this is
EPA's RfD for nitrate. The critical effect, upon which the RfD is
based, is toxicity to infants after a short-term exposure. In this
case, harmonic mean flow would be an inappropriate design flow for such
a short-term effect. In this case, a 7Q10 or a 4Q3 design flow may be
more appropriate.
H. What Is the Relationship Between the Agency's Recommended Section
304(a) Water Quality Criteria and Drinking Water Standards?
EPA recommends that States and authorized Tribes use this 2000
Human Health Methodology to develop their own AWQC for all pollutants
of concern using the latest scientifically defensible data and
principles. Sources of scientifically defensible data include published
toxicological literature or recent EPA assessments, including those
that underlie IRIS values, the most recently published recommended
Section 304(a) water quality criteria or the most recently promulgated
SDWA MCLGs.
When adopting water quality criteria to protect CWA Section 101(a)
fishable uses, States and authorized Tribes need to ensure such
criteria adequately address fish consumption as an exposure route.
When States and authorized Tribes do not develop their own AWQC,
EPA recommends that States and authorized Tribes use the most recently
published recommended Section 304(a) water quality criteria for ``water
and organisms'' based on this new Human Health Methodology to protect
CWA Section 101(a) fishable uses and waters designated for drinking
water. This ensures that the water quality criteria adequately address
fish consumption, bioaccumulation and drinking water uses.
When EPA publishes the annual compilation of new and revised
national recommended Section 304(a) water quality criteria, those
criteria represent the Agency's most current recommended Section 304(a)
water quality criteria and should be used by States and authorized
Tribes when reviewing their water quality standards.
When States and authorized Tribes do not develop their own AWQC,
and there are no recommended Section 304(a) water quality criteria for
a pollutant of concern, or the recommended Section 304(a) water quality
criteria have not yet been revised based on this new Human Health
Methodology \1\:
---------------------------------------------------------------------------
\1\ New criteria and criteria revised under this new Methodology
are published annually as the ``Compilation of National Recommended
Water Quality Criteria and EPA's Process for Deriving New and
Revised Criteria'' at www.epa.gov/ost/standards/.
---------------------------------------------------------------------------
1. For a pollutant for which EPA has published a recommended
Section 304(a) water quality criterion for ``water and organisms''
based on the 1980 Methodology and for which EPA has not promulgated an
MCLG, EPA will recognize the current Section 304(a) water quality
criterion, or a criterion that is developed or revised pursuant to the
2000 Human Health Methodology and approved by EPA.
2. For a pollutant for which EPA has published a recommended
Section 304(a) water quality criterion for ``water and organisms''
based on the 1980 Methodology and for which EPA has more recently
promulgated an MCLG, EPA generally recommends the MCLG for
noncarcinogenic pollutants, or a criterion derived by recalculating the
MCLG at an acceptable cancer risk level (i.e., a level within the range
of 10-6 to 10-5, as specifically discussed in
Section II.D, which notes that special scientific circumstances and
assessment of natural contaminants may lead to numbers outside the to
10-6 to 10-5 risk range).
3. For a pollutant for which EPA has not published a recommended
Section 304(a) water quality criterion for ``water and organisms'' and
for which EPA has promulgated an MCLG, EPA generally recommends the
MCLG for noncarcinogenic pollutants, or a criterion derived by
recalculating the MCLG at an acceptable cancer risk level (i.e., a
level within the range of 10-6 to 10-5, as
specifically discussed in Section II.D, which notes that special
scientific circumstances and assessment of natural contaminants may
lead to numbers outside the 10-6 to 10-5 risk
range).
EPA no longer recommends that an MCL be used where consideration of
available treatment technology, costs, or availability of analytical
methodologies
[[Page 66451]]
has resulted in an MCL that is less protective than an MCLG.
States and authorized Tribes continue to have the flexibility to
adopt water quality criteria that are more protective than EPA's
recommendations, as long as such criteria are protective of the
designated uses and scientifically defensible.
I. How Are Health Risks to Children Considered in the Methodology?
In recognition that children have a special vulnerability to many
toxic substances, EPA's Administrator directed the Agency in 1995 to
explicitly and consistently take into account environmental health
risks to infants and children in all risk assessments, risk
characterizations and public health standards set for the United
States. On April 21, 1997, President Clinton signed Executive Order
13045, ``Protection of Children From Environmental Health Risks and
Safety Risks,'' which assigned a high priority to addressing risks to
children. In May 1997, EPA established the Office of Children's Health
Protection to ensure the implementation of the President's Executive
Order (E.O.). Circumstances where risks to children should be
considered in the context of the 2000 Human Health Methodology are
discussed in the Noncancer Section (in terms of developmental and
reproductive toxicity) and in the Exposure Section (for appropriate
exposure intake parameters).
All of EPA's risk assessment guidelines should be consulted when
conducting a risk assessment to ensure that information from studies on
carcinogenesis and other health effects are considered together in the
overall characterization of risk. This is particularly important in the
case in which a precursor effect to tumor is also a precursor or
endpoint of other health effects and is used in dose-response
assessment. The overall characterization of risk will be the basis for
carrying out assessments of instances in which fetuses, infants, or
children are at risk.
III. Summary of Comments Received on the 1998 Draft Methodology
Revisions and EPA's Responses
A. Implementation
1. Application of Human Health Water Criteria Within Mixing Zones
Comments--Commenters stated that human health criteria should start
with the local relevant fish consumption rates and then make
adjustments to reflect the actual relevant fish consumption rate
related to the discharge and the mixing zone. It was also suggested
that implementation in the NPDES program inherently needs a translator
mechanism to adjust the standards to reflect actual consumption
associated with allowed mixing zones.
Response--Application of human health water criteria within a
mixing zone is not within the scope of this Methodology. At this time,
EPA's current recommendations regarding the application of human health
criteria within mixing zones are contained in the Technical Support
Document for Water Quality-Based Toxics Control (USEPA, 1991b) and the
Water Quality Standards Handbook (USEPA, 1994). We also note that
mixing zones are an optional policy that not every State and authorized
Tribe has adopted into their water quality standards. For States and
Tribes that have authorized mixing zones, the designated uses of a
waterbody as a whole must be maintained and protected.
2. Application of Human Health Water Quality Criteria to Marine Waters
Comment--A question was raised as to whether human health water
quality criteria are applicable to marine waters, given the vastness of
most marine waters.
Response--EPA believes human health water quality criteria should
be applied to near-shore waters (specifically within a three-mile
limit) wherever dischargers are located to protect aquatic food
organisms, but not to include the drinking water consumption parameter.
These water quality criteria are then used to derive permit limits that
will ensure water quality criteria are not exceeded within the vicinity
of an outfall. This protects organisms that are sessile and other
organisms that may be attracted to the effluent and that are food
sources. In the absence of data specific to the coastal site indicating
that particular marine species are impacted by those discharges, we
recommend our human health criteria to protect coastal waters. [Note:
EPA's recommended national default fish intake value, which excludes
marine species, supports this position. Estuarine species that are more
likely to be found in near-shore waters are included in the default
intake value. Potential exposure from open-ocean marine species are not
ignored; the marine species exposure pathway can be accounted for as
part of the RSC factor.]
3. Cancer Risk Range
Comments--Many comments were received on the appropriateness of the
cancer risk range. Numerous commenters stated that the permissible
range and recommended default of 10-\6\ are appropriate and
approved of the range's consistency with other Agency programs. EPA was
asked to reconcile the statements that both 10-\6\ and
10-\5\ are acceptable for the general population, that
10-\6\ is appropriate for promulgation of Federal water
quality standards under Section 303(c) given that we have said
10-\5\ is appropriate for the Great Lakes, and that a
10-\5\ risk level along with a 17.8 g/day fish intake
assumption will protect the highest consumers at a 10-\4\
risk level. Other comments are listed as follows.
The Methodology should use a 10-\5\ risk level.
10-\6\ represents a change in the acceptable
risk level.
The 10-\6\ risk level represents a binding
regulatory constraint that will provide no State flexibility.
10-5 is used by most States, and EPA should
retain this default because the Agency has not determined that it is
inadequate.
A range of 10-4 to 10-5 is
advocated.
In addition, we received comments that allowing highly exposed
groups to potentially experience cancer risks an order of magnitude
higher than the general population is unjust and disregards Native
American treaty rights. A commenter supported the idea that a
10-4 risk level can be protective and believed highly
exposed populations are few in number. Another stated that the cancer
risk range should apply to total contaminants (i.e., a cumulative
cancer risk ceiling). It was cautioned that the concept of relative
risk could result in selection of inappropriate target populations and
intake rates. Others agreed that States and authorized Tribes should
have the flexibility to select cancer risk levels as risk management
decisions and requested that EPA explicitly state that it will support
risk levels chosen by a Tribal authority, while another requested the
flexibility without requiring involved demonstrations specific to the
subpopulation at issue. A commenter recommended changes in EPA's
Methodology to ensure that the resulting water quality criteria are
more applicable to exposed populations. Others asked EPA to indicate
the percentile of the exposed population that would meet the
10-6 risk level.
Response--With the 1980 Methodology, EPA presented three separate
304(a) criteria for carcinogens at risk levels corresponding to
10-7, 10-6, and 10-5 for States and
authorized Tribes to choose from. However, the 10-7 risk
level has not been used by any State or authorized
[[Page 66452]]
Tribe when adopting water quality standards. Furthermore, since that
time, EPA's guidance and regulatory actions have utilized a
10-6 risk level as an appropriate target risk for the
general population.
With the 2000 Human Health Methodology, our position is that both
10-6 and 10-5 are appropriate targets for health
protection of the general population and that highly exposed
populations should not exceed a 10-4 risk level. We also
note that special scientific circumstances and assessment of natural
contaminants may lead to numbers outside the 10-6 to
10-5 range. However, we are not automatically assuming that
10-5 will protect ``the highest consumers'' at the
10-4 risk level. One commenter referred to specific data
indicating high intake levels that would not satisfy such an
assumption. Nor are we advocating that States and authorized Tribes
automatically establish criteria based on assumptions for highly
exposed population groups at the 10-4 risk level. We
acknowledge that fish consumption rates vary considerably, especially
among subsistence populations, as is evident from the studies
summarized in the Exposure TSD. Indeed, it is the variation of fish
consumption among these population groups that could make either
10-5 or 10-6 protective of those groups at a
10-4 risk level. Specifically, if a State adopted a
criterion based on a 10-5 risk level and a 17.5 g/day
consumption rate, a high-end subsistence consumption of 1,750 g/day
would exceed a 10-4 risk level.
It is important to understand that criteria for carcinogens are
based on chosen risk levels that inherently reflect, in part, the
exposure parameters used to derive those values. Therefore, changing
the exposure parameters will also change the risk. Specifically, the
incremental cancer risk levels are relative, meaning that any given
criterion associated with a particular cancer risk level is also
associated with specific exposure parameter assumptions (i.e., intake
rates, body weights). When these exposure values change, so does the
relative risk. As we have previously indicated for a criterion derived
on the basis of a cancer risk level of 10-6, individuals
consuming up to 10 times the assumed fish intake rate would not exceed
a 10-5 risk level. Similarly, individuals consuming up to
100 times the assumed rate would not exceed a 10-4 risk
level. Thus, for a criterion based on EPA's default fish intake rate
(now 17.5 g/day, based on the most recent survey data) and a risk level
of 10-6, those consuming a pound of fish per day would
potentially experience between a 10-5 and a 10-4
risk level (closer to a 10-5 risk level). Even if a
criterion were based on high-end intake rates and the relative risk of
10-6, then an average fish consumer would not exceed a
cancer risk level of approximately 10-8. The point here is
that the risks for different population groups are not the same.
EPA believes that the adoption of a 10-6 or
10-5 target risk level, both of which States and authorized
Tribes have historically chosen, represents a generally acceptable
health protection decision, noting again that special scientific
circumstances or assessments of natural contaminants may necessitate
additional considerations. EPA recommends adoption of water quality
standards that include water quality criteria based on either the
10-5 or 10-6 risk level if the State or
authorized Tribe has identified the most highly exposed subpopulation,
has demonstrated that the chosen risk level is adequately protective of
the most highly exposed subpopulation, and has completed all necessary
public participation. States and authorized Tribes also have
flexibility in how they demonstrate this protectiveness and obtain such
information. A State or authorized Tribe may use existing information
as well as collect new information in making its determination as to an
appropriate level of protection. In addition, if a State or authorized
Tribe does not believe that the 10-6 risk level adequately
protects highly exposed subpopulations, water quality criteria based on
a more stringent risk level may be adopted. However, we are now adding
that a generally specific analysis should be made and presented to
ensure that highly exposed groups do not exceed a target
10-4 risk level. In cases where fish consumption among
highly exposed population groups is of a magnitude that such a
10-4 risk level would be exceeded, a more protective risk
level should be chosen. These determinations should be made by the
State or authorized Tribe and are subject to EPA's review under Section
303 of the CWA. Guidance on choosing appropriate exposure parameters is
discussed in both the 2000 Human Health Methodology and the Exposure
Assessment TSD.
Given the relatively significant variation in fish consumption
rates, EPA intends to derive Section 304(a) criteria at the
10-6 risk level, based on an intake rate of 17.5 g/day. We
believe that basing our 304(a) criteria on general U.S. population
exposures is most appropriate, given their use as a default value for
the nation as a whole. Most States have, in fact, already adopted a
10-6 risk level with their criteria for carcinogens, not the
10-5 risk level claimed by one commenter. This default
would, in turn, be protective for fish intakes of up to 1,750 g/day at
the 10-4 risk level. However, in the Exposure Assessment
TSD, EPA has recommended that States and authorized Tribes give
priority to identifying and adequately protecting the most highly
exposed population by adopting more stringent criteria, if the State or
authorized Tribe determines that the highly exposed population would
not be adequately protected by criteria based on protecting the general
population. States and authorized Tribes have the option to derive
their criteria at a 10-6 risk level, as EPA will do with its
304(a) criteria. They also have the flexibility to combine the
10-6 risk level with fish consumption rates for highly
exposed population groups. Thus, States and authorized Tribes may
choose to adopt criteria that are more protective than EPA's 304(a)
criteria. We intend to support the health protection decisions made by
States and authorized Tribes as long as they use the risk range that
EPA has stated here and in the 2000 Human Health Methodology. EPA has
made reasonable and conservative assumptions in choosing exposure
parameters with the goal of protecting the majority of the population.
However, we do not believe it is possible to calculate the exact
percentile of the population that would be protected at a given risk
level in terms of the overall combination of exposure parameters. We
emphasize that the criteria are derived to be protective, not
predictive of an exact percentile of the total population that is
protected.
Regarding the use of a 10-5 risk level in the Great
Lakes Water Quality Initiative (GLI), the criteria values were based on
fish consumption estimates that reflected intake data among
sportfishers, a group that consumes more fish than the general
population. Again, we recommend that States and authorized Tribes base
their criteria on more highly exposed population groups, if they would
not be adequately protected by criteria based on intake rate estimates
for the general population. Regarding the application of a cumulative
cancer ceiling, the commenter has misunderstood EPA's policy when
setting 304(a) criteria for carcinogenic effects based on linear low-
dose extrapolation. With these carcinogens, the AWQC are set with
respect to the incremental lifetime risk posed by the substance in
water and are
[[Page 66453]]
not being set on an individual's total cancer risk from all sources of
exposure.
4. Coordinating the Human Health Methodology With Other EPA Programs
Comments--Numerous commenters recommended that the Methodology
revisions be coordinated with the drinking water program (specifically,
MCLs/MCLGs required under the SDWA) and believed that the drinking
water portion of AWQC and MCLGs should be equivalent. Several
commenters stated that the burden of achieving health goals should be
borne by dischargers and other polluters, not by water users or the
environment. Commenters also recommended that EPA use MCLs when AWQC
are less protective or for chemicals when AWQC do not exist. Another
recommended that an additional margin of safety be included if the MCL
were used, in particular for chemicals not effectively removed by
conventional drinking water treatment, and also stated that neither the
availability of MCLs or MCLGs should deter development of AWQC. Some
commenters believed that the use of an MCLG is an acceptable
alternative for chemicals of drinking water concern because, like the
AWQC, it is a health-based value. However, others recommended that
MCLGs not be used when they are more stringent than AWQC because they
are not regulatory standards. Two commenters stated that EPA should not
abandon its policy of setting AWQC for carcinogens at zero for
``maximum protection of human health'' and recommended that the ``Group
C'' chemicals also have AWQC set at zero (referring to non-zero MCLs as
inconsistent with the intent of a zero MCLG). However, other commenters
recommended that AWQC be set at one-half of the MCL when the MCLG is
zero, at a 10-6 risk level, or by calculating both and
choosing the lower of the two. Two commenters urged EPA to unify the
national Human Health Methodology with the GLI guidance. Another
discussed microbial pathogens and, in addition to recommending
development of criteria for specific microbial contaminants,
recommended coordination with the drinking water program [i.e., the
SDWA's Candidate Chemical List (CCL)] and stated that microbial
criteria need to be set for more than recreational waters.
Response--EPA intends to continue deriving AWQC that include a
drinking water pathway, applicable to waters that are potential sources
of drinking water, and agrees that the drinking water component of AWQC
should be consistent with the MCLG (if one has been established).
Therefore, we intend to use a similar methodology for deriving AWQC and
MCLGs. We also intend to coordinate with the Agency's safe drinking
water program when prioritizing chemicals for AWQC derivation/revision
(see also response to Comment A.11, Proposed Chemical List). Regarding
the relationship between AWQC and the drinking water MCLs and MCLGs, we
have clearly stated our position in the Federal Register Notice for the
1998 draft Methodology revisions (USEPA, 1998c) on this relationship
and our approach to considering when an MCL or MCLG may be appropriate
to use in lieu of AWQC. That discussion is excerpted in the 2000 Human
Health Methodology document, along with clarification of our policy on
the circumstances and limitations under which either should be used. We
do not necessarily assume that a chemical's concentrations in ambient
waters and drinking water are equivalent but are aware that chemicals
may not be effectively removed by conventional drinking water
treatment.
Commenters who referred to EPA's abandonment of its policy of
setting AWQC for carcinogens at zero have substantively misstated our
policy based on both the 1980 Methodology for deriving AWQC and our
1998 draft Methodology revisions, and are directed to the Federal
Register Notice cited above. We did state in our 1980 Methodology that
for the maximum protection of human health from potential carcinogenic
effects, the ambient water concentration should be zero, based on an
assumption of a linear dose-response relationship at low doses. The
1980 Methodology also indicated that zero levels may not have been
attainable at that time. This remains the case at present. The
combination of background levels of carcinogens from natural sources
and global background levels from anthropogenic sources make attainment
of zero levels for many potential carcinogens impossible. In addition,
more recent and sophisticated toxicological information on
carcinogenicity suggests modes of action for carcinogens that would
lead to nonlinear low-dose extrapolation. Note that the 1980
Methodology preceded the Agency's original 1986 cancer guidelines,
which are now being revised. We are maintaining our policy to derive
AWQC for carcinogens to correspond to incremental lifetime cancer risk
levels, applying a risk management policy that ensures a reasonable
level of protection for the general population.
When EPA developed the methodology to derive human health criteria
for the waters of the Great Lakes System, the Agency was mindful of the
need for consistency with the planned changes in the Human Health
Methodology presented today for deriving national AWQC for the
protection of human health. Throughout the 1998 draft Methodology
revisions, references were made to comparisons of the two
methodologies, especially whenever differences occur due to regional
exposure assumptions made for the Great Lakes System. The GLI guidance
consisted of water quality criteria, detailed methodologies to develop
criteria for additional pollutants, implementation procedures, and
antidegradation policies and procedures tailored to the Great Lakes
system; these reflected the unique nature of the Great Lakes ecosystem.
Those States and authorized Tribes are to use the GLI methodology to
establish criteria for the waters of the Great Lakes system, which
allows appropriate flexibility to States and authorized Tribes to
develop equitable strategies to control pollution sources and to
promote pollution prevention practices. The 2000 Human Health
Methodology is undertaken pursuant to Section 304 of the CWA, and is
independent of, and does not supersede, the GLI. Although consistency
in State water quality standards programs is an important goal for EPA,
we also recognize that it is necessary to provide appropriate
flexibility to States and Tribes, both Great Lakes States and non-Great
Lakes States, in the development and implementation of place-based
water quality programs. Recognition of a general need for flexibility
is not incompatible with the requirements for the Great Lakes States
and Tribes established in Section 118(c)(2) of the CWA. We have
harmonized the two, where appropriate, while maintaining parameters and
provisions that are appropriate for Great Lakes-specific criteria.
EPA has identified development of microbial water quality criteria
as part of its strategy to control waterborne microbial disease, by
controlling pathogens in waterbodies and by protecting designated uses,
such as recreation and public water supplies. The program fosters an
integrated approach in order to protect both ground-water and surface
water sources. EPA plans to conduct additional monitoring for
Cryptosporidium parvum and Escherichia coli, and determine action plans
in accordance with the results of this monitoring.
5. Designated Uses
Comments--Commenters indicated that designated uses for waterbodies
[[Page 66454]]
that cross State boundaries and that fail to take into account
downstream uses may effectively prohibit downstream waters from being
used as a water supply; the AWQC should reflect the use of a waterbody
as a drinking water source unless the use patterns of the entire
waterbody indicate that this is not a current or future possibility.
Response--EPA regulations at 40 CFR 131.10(b) state:
In designating uses of a water body and the appropriate criteria
for those uses, the State shall take into consideration the water
quality standards of downstream waters and shall ensure that its
water quality standards provide for the attainment and maintenance
of the water quality standards of downstream waters.
We believe this requirement is sufficient to address the concerns
raised by the commenter and to ensure downstream uses are maintained
and protected.
6. Developing National 304(a) Criteria
Comments--Commenters stated that EPA should not derive national
304(a) AWQC and stated their preference for regional measurements, and
that national 304(a) criteria could be overly stringent or
underprotective from State to State. Instead, they recommended that EPA
simply provide specific ``algorithms'' to force States to develop their
own criteria. However, they also said that EPA should develop a single
criterion for each chemical based on the most relevant toxic endpoint
and appropriate target population. A commenter recommended that EPA
develop criteria for both cancer and noncancer endpoints because their
comparative protectiveness may not be clear until permit limit design
flows are determined. Another commenter stated that relying on default
parameter values would inhibit the process for developing criteria/
implementing standards because the regulated community will not accept
such criteria. Two commenters stated that the amount of information on
adverse impacts to water quality, fish, birds, wildlife, and human
health warrants regulatory action to eliminate those toxicants. They
recommended that EPA include all biotic pathways using the water
source, including wildlife and plant life, and advocated protecting
cultural and religious uses. A commenter stated that limited
information exists for development of criteria in arid regions and that
resources would be better spent gaining knowledge on the impacts of
chemicals in regional watersheds. Another questioned how AWQC can be
derived when ambient levels are below analytical detection limits.
Several commenters supported the derivation of fish tissue criteria.
Response--Section 304(a) of the CWA requires EPA to develop
national water quality criteria recommendations for States and
authorized Tribes to use as guidance in adopting water quality
standards. It is not an option for EPA to ignore this requirement. As
such, the national 304(a) criteria that EPA periodically publishes are
generally applicable to the nation's waters. Although we encourage
States and authorized Tribes to use the Methodology to develop criteria
based on local/regional information and believe that water quality
criteria reflecting such local conditions are desirable, we have not
abandoned our obligations under the CWA. The commenter should be aware
that States have adopted EPA's recommended 304(a) criteria.
Furthermore, in contrast to another commenter's suggestion, under the
CWA, 304(a) criteria are not enforceable regulations; these criteria
are guidance and do not impose legally binding requirements.
States and Tribes always have the option to undertake their own
evaluations to develop water quality criteria, as long as such criteria
are consistent with the CWA and the implementing Federal regulations.
States have derived water quality criteria for their waters in the
absence of EPA guidance and may continue to do so. However, the
recommended criteria serve as guidance to States and authorized Tribes,
and EPA cannot force States or Tribes to conduct their own evaluations.
We are well aware that the resources and expertise within States and
Tribal authorities vary greatly and, while encouraging them to pursue
their own criteria development programs, we anticipate that many will
continue to rely on our expertise and recommended 304(a) criteria. We
included guidance on site-specific modifications for States and
authorized Tribes to derive their own water quality criteria and will
expand this information as part of the TSD volumes for the 2000 Human
Health Methodology.
Although we have provided numerous default parameter values for
different population groups, we intend to derive or revise AWQC based
on the most sensitive health endpoint and the population group most
relevant for that endpoint. Regarding measurable levels of chemicals in
the water column, the CWA clearly states that limitations in analytical
methods will not be considered when deriving AWQC. Rather, the AWQC
represent health-based considerations only. However, analytical method
limitations are taken into account in the implementation of water
quality standards. We believe that deriving AWQC based on fish tissue
concentrations may be appropriate in some instances to overcome this
problem when there is a health concern for that chemical (for greater
discussion of fish tissue criteria, see response to Comment F.7).
Regarding cancer versus noncancer endpoints, it is EPA policy to
develop criteria for the most sensitive endpoint in order to be
protective of both potentially relevant cancer and noncancer effects.
EPA intends to continue this practice. Regarding design flows, see the
response on this issue under Comment A.9. Finally, these Methodology
revisions apply to the protection of human health only. Other EPA
efforts to develop methods and criteria for the protection of birds or
other wildlife are not part of this guidance and will not be addressed
here. Considerations such as religious or cultural uses cannot be
quantitatively factored into the AWQC equation for setting pollutant
criteria values.
7. Developing Organoleptic Criteria
Comments--Commenters suggested that EPA should provide guidance for
States to develop organoleptic criteria for ambient waters that are
sources of drinking water, and develop specific organoleptic criteria.
Taste and odor are strongly associated with consumer perceptions and
confidence in water quality. They suggested that EPA should provide
organoleptic criteria and allow States to make decisions about their
use. Others stated that organoleptic criteria should not be developed
because they are not relevant to protection of human health and because
they should only be considered for drinking water standards.
Response--The 2000 Human Health Methodology is focused on deriving
toxicity-based criteria because they, not organoleptic criteria, are
directly related to potential adverse human health effects. We have
received much support for our position on this issue since initiating
the Methodology revisions. EPA acknowledges that if organoleptic
effects (i.e., objectionable taste and odor) cause people to reject the
water and its designated uses, then the public is effectively deprived
of the natural resource. EPA encourages the development of organoleptic
criteria when States and Tribes believe they are needed to protect
designated uses and have indicated this in the 2000 Human Health
Methodology.
[[Page 66455]]
8. Establishing EPA's Most Recent Federally Recommended Water Quality
Criteria
Comment--A commenter stated that the proposed California Toxics
Rule (CTR) established EPA's most recent federally recommended water
quality criteria, and because EPA did not propose to promulgate arsenic
in the CTR, there is no federally recommended water quality criterion
for arsenic.
Response--With regard to arsenic and the Agency's policy on
applicable 304(a) criteria, EPA clearly stated in the 1998 draft
Methodology revisions that until such time as the Agency re-evaluates a
chemical and subsequently publishes revised chemical-specific 304(a)
criteria, the existing criteria remain in effect. Although the 2000
Human Health Methodology represents improvements to the 1980
Methodology, EPA believes that the existing 304(a) criteria are
fundamentally sound from a scientific standpoint. We have long
supported this position. Our recommended water quality criterion for
arsenic remains the value published in EPA's Goldbook in 1986 (USEPA,
1986d) and promulgated in 1992 as part of the NTR. Federal
promulgations for individual States take into account the needs of the
individual State and site-specific conditions of waterbodies within the
State. Federally promulgated water quality standards for a State may
not always result in water quality criteria that are nationally
applicable. We understand there has been some confusion regarding the
current recommended water quality criteria in light of State-specific
promulgations, and as a result, in 1998, we published National
Recommended Water Quality Criteria (USEPA, 1998b) to clarify our
national recommendations. This list will be updated approximately on an
annual basis to contain our most current recommended water quality
criteria for States and authorized Tribes to use as guidance in
adopting water quality standards.
9. Flows
Comment--Comments received suggested that EPA should adequately
consider and account for regional differences, such as highly variable
flows, lower exposures, and lack of fish habitat due to no-flow
conditions in many Southwestern washes (i.e., waterbody flow only
following a storm event).
Response--EPA believes there is sufficient flexibility in the
current regulatory program for States to modify designated uses and
water quality criteria to protect those uses to address the conditions
that exist in waterbodies such as intermittent streams and washes.
Modifications to the water quality standards program are unwarranted at
this time.
10. Implementation on a Waterbody Basis
Comment--Commenters stated that human health criteria should be met
within the waterbody on a long-term average basis instead of short-term
maximums never to be exceeded. It was recommended that States be able
and even encouraged to develop site-specific standards for waterbodies
to reflect relevant fish consumption rates.
Response--The 2000 Human Health Methodology incorporates long-term
exposure into the development of water quality criteria. Determination
of when human health criteria are met within the waterbody is beyond
the scope of this document. However, EPA guidance addresses this issue
(USEPA, 1991b). We recommend harmonic mean flow to calculate permit
limits and taking the geometric mean of ambient water samples to
determine attainment. Both of these recommendations account for the
long-term exposure effects of chemical water quality criteria.
EPA recommends that States develop site-specific water quality
criteria to reflect relevant fish consumption rates. We have published
default fish consumption rates in the Methodology as recommendations to
States and Tribes in adopting water quality standards when a State or
Tribe lacks information on local fish consumption rates. EPA's
preference, however, is that States and Tribes adopt human health
criteria reflecting local fish consumption rates.
11. Proposed Chemical List
Comments--Commenters suggested that EPA integrate the AWQC
prioritization process with the drinking water program (i.e., with the
Candidate Contaminant List). Other comments suggested that EPA's short
list of pollutants (for revision) would result in a greater burden for
States that will need to develop more criteria. EPA was asked to
strengthen efforts to develop criteria for persistent chemicals and to
add endocrine disruptors. It was pointed out that the short priority
list published in the 1998 draft Methodology revisions includes
numerous banned pesticides. Additional chemicals and microbial
contaminants for EPA to consider in its prioritization of criteria to
revise/develop are suggested, as follows:
Atrazine
Benzo(a)pyrene
Chlordane
Cryptosporidium parvum strains
Cyanazine
Endrin
Giardia lamblia
Heptachlor
Heptachlor epoxide
Hexachlorobenzene
Methyl-tertiary-butyl-ether (MTBE)
Lead
Other PAHs (specifically advocated use of Relative Potency Factors)
Total Organic Carbon (TOC)
Toxaphene
Response--We will evaluate all suggested pollutants based on the
following factors: relative toxicity; occurrence in fish tissue, water,
and sediments (frequency as well as concentration levels); and for
chemicals, information on the chemical's bioaccumulation. This
strategy, previously published in the 1998 draft Methodology revisions,
received general support, and we will consider these suggestions along
with priorities identified by both the Office of Pesticide Programs and
the Office of Ground Water and Drinking Water, and other input received
from States and Tribes. Regarding a State's need to revise more
criteria, see the response to Comment A.13, Revising Existing 304(a)
Criteria.
12. Publishing Existing 304(a) Criteria Information
Comments--EPA received support for its proposal to occasionally
publish a list of its criteria and information on revisions or new
criteria in progress. Some commenters stated that EPA should publish a
list in the Federal Register annually, and one suggested that EPA post
any changes during the interim on the Agency's website. It was also
suggested that EPA should identify which criteria were changed and why.
One commenter stated that a timeframe of 3 to 5 years is more
appropriate because little is likely to change in just one year.
Another commenter expressed support for publishing an annual list of
EPA drinking water regulations and health advisories.
Response--EPA believes that regular updates on its website are the
most efficient way to make accurate information available to the
public. We hope this will be helpful for States and authorized Tribes
in reviewing and revising their water quality standards during the
triennial reviews required under 40 CFR 131. We will consider further
the circumstances and frequency with which Federal Register
publications may be used. The commenter who referred to drinking water
standards and health advisories misunderstood EPA's intention, which is
to publish a list annually on the
[[Page 66456]]
304(a) water quality criteria similar to that done for the drinking
water program.
13. Revising Existing 304(a) Criteria
Comments--EPA received support for revising its Methodology and for
providing clear indication of the scientific components versus the
science policy components. Commenters supported the idea of EPA
revising criteria based on partially updated components of the criteria
equations. One expressed a preference for comprehensive revisions but
also stated that partial updates should be done as soon as possible,
referring to components such as fish consumption rates and
``interspecies conversion of doses'' as those that can automatically be
inserted, thereby enabling revision of all criteria within a week of
effort. [Note: It is unclear whether the commenter is referring to the
new body weight/surface area scaling factor or something else by the
term ``interspecies conversion of doses,'' because it is not
specified.] A commenter stated that as any component is updated, so
should the criteria. Another suggested that EPA partially revise all
criteria for the components that current information would allow. On
the other hand, a commenter stated that EPA should not revise criteria
based on the new scaling factor or other pieces of data, but should
conduct literature searches for new available data applicable to the
Methodology. Other comments were that priority should be given to
chemicals with significant new toxicity information; the use of partial
updates is not scientifically sound, will produce overly conservative
criteria, and restricts the public's right to comment; and all revision
actions should be subject to public review and comment.
Response--EPA ideally seeks to conduct re-evaluations of every
component used in the derivation of 304(a) criteria before revising any
criteria. However, we have discussed updating a limited number of
304(a) criteria over the course of the next several years based on one
or more components of the criteria equation (a ``partial update'')
rather than a complete set of components, realizing that updating some
of these (e.g., the BAF, the exposure parameters) is not as time-or
resource-intensive as completing a toxicological evaluation. Recent
actions taken by EPA represent this option; both the NTR and the GLI
were partial updates. We intend to focus our limited resources on
revising (either partially or completely) those pollutants that we
consider highest priority in terms of both toxicological concern and
frequency of occurrence.
EPA has indicated that it does not believe it is desirable to
revise criteria based on piecemeal information, such as the
interspecies scaling factor, when there may be other information (e.g.,
new toxicity studies) that could also change the risk assessment and,
thus, the criteria. We have also cautioned the States and Tribes not to
selectively apply data or methods that would inaccurately characterize
risk (e.g., in order to ensure a water quality criterion that is less
stringent than an EPA 304(a) criterion). For a water quality criterion
revision based on a partial update to be considered acceptable to EPA,
a component of the criterion (e.g., the toxicological risk assessment)
would need to be comprehensive (e.g., a new or revised RfD or cancer
dose-response assessment, as opposed to simply a new scaling factor),
should stand alone and be based on new national or local data. A
toxicological update should be on a weight-of-all-of-the-evidence
basis, as called for under EPA's risk assessment guidelines. This
should incorporate the latest published toxicological literature and
risk assessment approaches. States or authorized Tribes seeking to
establish ambient water quality criteria are urged to continue using
the IRIS noncancer and cancer risk assessments if they cannot conduct a
complete evaluation to update toxicological values.
The Agency has developed an improved process that it intends to use
when deriving new criteria or conducting a major reassessment of
existing criteria. The process is intended to provide expanded
opportunities for public input and to make the process more efficient.
When deriving new criteria or when initiating a major reassessment of
existing criteria, we will publish a notice in the Federal Register and
on the EPA website announcing our assessment or reassessment of the
pollutant. References relied on will be provided, and we will solicit
additional data or information useful in deriving new or revised
criteria. After input is received and evaluated, we will develop draft
recommended water quality criteria. Next, EPA will initiate an
independent external peer review of the draft criteria. The public will
also be able to submit views on issues of science pertaining to the
information used in deriving the draft criteria. We will then revise
the draft criteria as necessary, incorporating peer review and public
input, and announce the availability of the final water quality
criteria in the Federal Register and on the EPA website. In addition to
developing new criteria and conducting major reassessments of existing
criteria, EPA also from time to time will partially revise criteria
based on new information pertaining to individual, stand-alone
components of the criteria. Because such recalculations normally result
only in changes to single parameters of the criteria (not in the
underlying scientific methodologies) and reflect peer-reviewed data,
EPA will typically publish such recalculated criteria directly as the
Agency's recommended water quality criteria. If substantial revision is
done, we will follow the process of peer review and public input
outlined above. Further discussion of this process can be found in the
Federal Register Notice compilation of recommended water quality
criteria and notice of process for new and revised criteria (USEPA,
1998e).
14. State Evaluation of Data Supporting Criteria
Comment--One commenter asserted that ``states should be allowed to
critically evaluate all data and disregard data that, for one reason or
another, are unrepresentative or unreliable'' and further asserted that
States should be allowed to critically review EPA's published 304(a)
criteria and to decline to adopt any criteria they feel are
inappropriate.
Response--EPA disagrees with underlying assumptions of the comment.
EPA's 304(a) criteria are guidance. States and authorized Tribes may
develop their own scientifically defensible, peer-reviewed criteria.
Moreover, States and any other interested parties have the opportunity
to participate in development of water quality criteria published under
Section 304(a) of the Act. Prior to publishing any new or revised
304(a) criteria, EPA provides stakeholders with an opportunity to
review and provide scientific views. EPA maintains that at the time of
publishing of new or revised 304(a) criteria, the criteria are
scientifically defensible and establish guidance to States for adopting
water quality standards under section 303(c) of the Act. Under 40 CFR
131.11, States continue to have the option of adopting water quality
criteria based on 304(a) criteria modified to reflect site-specific
conditions, or other scientifically defensible methods.
15. Streamlined Approach to Developing Criteria Documents
Comment--EPA received support for the streamlined format used in
the example criteria documents published in 1998.
Response--We acknowledge this support.
[[Page 66457]]
16. Treaty Rights and Trust Obligations/Government-to-Government
Relations
Comments--Commenters recommend EPA fully incorporate treaty rights
and Federal trust obligations to Indian tribes in its national AWQC
guidelines. It was reiterated that EPA has an obligation to maintain
government-to-government relations with Tribal Governments.
Response--As stated in the 1998 draft Methodology revisions, ``risk
levels and criteria need to be protective of tribal rights under
federal law (e.g., fishing, hunting, or gathering rights) that are
related to water quality.'' We believe the best way to ensure that
Tribal treaty and other rights under Federal law are met, consistent
with Federal trust responsibility, is to address these issues at the
time EPA reviews water quality standards submissions.
B. General Policy
1. AWQC Derivation Equation Errors
Comments--Commenters pointed out that the term ``RSC'' (relative
source contribution) in the Linear Cancer Effects equation of the 1998
draft Methodology revisions was incorrect and should have been ``RSD''
(risk-specific dose).
Response--The commenters are correct; this was a misprint and
should have been RSD for the linear equation.
2. Chronic Human Health Effects Assumption
Comments--EPA received support for its assumption that, by and
large, AWQC are set to protect against long-term (chronic) human health
effects.
Response--We acknowledge the commenter's support.
3. Protectiveness of the Methodology
Comments--A commenter stated that inherent uncertainties in EPA's
risk assessments make them useless and that EPA must adopt the most
conservative methodologies in order to protect human health, while also
acknowledging the presence of uncertainties in assessing adverse health
impacts. They suggested that EPA should tighten regulations for
chemicals of national priority, develop criteria for additional
priority chemicals, and take the most conservative approach regarding
reproductive and developmental effects. Other commenters advocated that
EPA incorporate pollution prevention policies into its risk assessment
methodologies. One commenter asked EPA to provide guidance to States
for developing AWQC less restrictive than AWQC for the general public,
and suggested that engineering and administrative controls could reduce
exposures. Another stated that the population groups identified
represent appropriate categories and that the corresponding default
parameter values are reasonable. The same commenter advocated use of
the same percentile value for each default parameter (``e.g., 95th
percentile''). Another commenter recommended that EPA determine
distributions of exposure in order to assess whether a significant
subgroup is more highly exposed than the general population, especially
in the context of the chosen exposure parameter values. Others stated
that the general population should not be targeted and that EPA should
instead target the population group most at risk, or that protection of
health should apply to all humans. Commenters also expressed
uncertainty over the segment of the population that the AWQC are
designed to protect, and questioned whether EPA would evaluate all
subpopulations for all chemicals. Two commenters requested an analysis
of the overall impact that each parameter has on the criteria and how
that relates to the conservativeness of the estimated risk, with one
criticizing EPA for not conducting probabilistic analyses of exposures
or other methods to evaluate the interaction of exposure parameters.
This commenter stated that the Agency has used ``high confidence-
level'' values for all parameter values and, therefore, the AWQC are
``inordinately conservative.'' Furthermore, EPA should specify the
level of protection within the high-end proportion of the general
population (e.g., ``the 95% level'') and adjust the exposure parameter
values within ``their defined distributions.'' Concern was expressed
that the flexibility regarding infants and children (i.e., for
developmental effects) conflicted with the fact that chronic lifetime
effects cover persons when they are children and adults. A commenter
recommended consideration of tissue effects, as well as organ-level
effects. Another stated that increasingly strict criteria/discharge
limits represent regulatory environmental injustice, and that
discharges in effluent-dependent streams are necessary for trees,
vegetation, and wildlife.
Response--EPA believes that it has made appropriately conservative
assumptions in conducting risk assessments where uncertainties exist.
Furthermore, for this effort we will rely on the Agency's peer-
reviewed, published risk assessment methodologies, which incorporate
procedures to address uncertainties in the risk assessments. We will
continue to make the most appropriate risk management decisions when
developing or revising criteria, including determining pollutants of
high priority. EPA does consider tissue-level effects in addition to
organ-level effects when conducting its risk assessments. We
acknowledge the comment regarding integrating pollution prevention
policies with our risk assessment methodologies and specifically
discuss this in the context of CWA goals in the 2000 Human Health
Methodology. We also believe that we have selected appropriate default
parameter values. Regarding the idea of criteria that are less
restrictive than EPA's 304(a) criteria, a State or authorized Tribe
would have such flexibility as long as it could clearly demonstrate
that the criteria it calculated would be protective of its population.
Such alternate assessments and the resulting proposed State or Tribal
standard would be subject to EPA's triennial review process.
Furthermore, the AWQC are health-based criteria, and therefore
potential effects of engineering and administrative controls are not
part of criteria.
By and large, the AWQC are derived to protect most of the overall
population from chronic adverse health effects. However, States and
authorized Tribes also need to understand that there are RfD's based on
developmental or other short-term adverse health effects, perhaps where
an exposure of one day could result in the effect. Long-term averaging
of exposure would not be appropriate in such circumstances. States and
authorized Tribes are also encouraged to consider protecting population
groups that they determine are at greater risk and, thus, would be more
protected using alternative exposure assumptions. We do not intend to
derive multiple criteria for all subpopulation groups for every
chemical. The commenter who discussed probabilistic analyses has
misunderstood EPA procedures. We have used median and mean values, and
percentile estimates, not high confidence-level values, as suggested by
the commenter. We also disagree that the resulting criteria represent
inordinately high levels of conservativeness. In general, we are doing
what the commenter recommended about targeting the overall protection
at the high end of the general population, even though the criteria
have not been subjected to an assessment of whether a 95% level has
been achieved (as recommended by the commenter). Although we have not
subjected the parameter values chosen
[[Page 66458]]
to a rigorous analysis, we have not used high-end percentiles for all
parameters. The assumed body weight value used is an arithmetic mean,
as are the RSC intake estimates of other exposures, when data are
available. The BAF component data values are based on median (i.e.,
50th percentile) values. The drinking water and fish intake values are
90th percentile estimates. We believe this will result in water quality
criteria that will be protective of a majority of the population. That
is our goal. The commenter has not provided a method that would allow
us to determine the overall percentile associated with the criteria
calculations. EPA has provided additional language in the 2000 Human
Health Methodology to clarify the population the AWQC are intended to
protect.
Finally, if EPA determined that pregnant mothers/fetuses or young
children are the population basis of a chemical's RfD or POD/UF, then
we would derive our 304(a) criteria using exposure parameter values for
that subgroup. This would be relevant only for less-than-lifetime
exposure situations and, therefore, does not conflict with the fact
that chronic health effects potentially reflect a person's exposure
during both childhood and adult years.
4. Setting Criteria to Protect Both Fish and Drinking Water Versus Fish
Only
Comments--EPA received strong support for deriving one AWQC value
to protect both drinking water and fish intakes and another to protect
for fish intakes only, given that the designated uses of waterbodies
vary and drinking water may not be a designated use. One commenter
stated that in addition to these two types of criteria, EPA should also
develop criteria for water ingestion only. They indicated that waters
may exist where fishing and consumption of fish are not relevant but
water ingestion is relevant. Furthermore, they pointed out that EPA's
Advanced Notice of Proposed Rulemaking for Water Quality Standards
discussed protection for aquatic life and, therefore, stated that
flexibility is needed so that fish consumption is not inappropriately
applied to all waters. A commenter questioned whether ambient waters
that are fished are also sources of drinking water, and whether
contaminant levels in the two water types could be equivalent. Others
stated that the drinking water pathway should not be included in the
AWQC, given the way AWQC are implemented (e.g., AWQC apply to waste
water discharges and MCLs apply to public drinking water system
exposures) and that MCLs may consider affordability and treatability. A
commenter stated that AWQC to protect fish/shellfish are not justified
and should be dealt with under other regulatory programs (e.g., the
Food Quality Protection Act).
Response--EPA believes that AWQC should include a drinking water
pathway to protect waters designated as potable water sources. (Also
see EPA's response to Comment A.4 regarding the relationship between
MCLs/MCLGs and AWQC, Coordinating the Human Health Methodology With
Other EPA Programs.) EPA strongly disagrees that AWQC to protect humans
exposed through consumption of fish/shellfish should not be developed.
Ensuring the protection of human health from consumption of
contaminated fish and shellfish is clearly within the requirements of
the CWA. We do not believe that 304(a) criteria to protect drinking
water uses only are particularly useful, because by and large, State
and Tribal standards for human health are set to protect waters with
multiple designated uses, not merely drinking water use. The water
quality standards program also protects aquatic life. The 2000 Human
Health Methodology will not change our requirement to apply aquatic
life criteria to protect aquatic species where they are more sensitive
(i.e., when human health criteria would not be protective enough) or
where human health via fish or water ingestion is not an issue.
5. Setting Criteria to Protect Against Multiple Exposures From Multiple
Chemicals
Comments--Several commenters thought EPA should consider multiple
chemical exposures when setting AWQC and consider these exposures
additive, at a minimum, while using information on synergistic impacts
from the combination of chemicals. Commenters also suggested that
certain Native American Tribes may have significant confounding factors
(not specified) to be considered with any synergistic assessment. A
commenter suggested that the cancer risk range apply to total
contaminants or that a cumulative cancer ceiling be established.
Another stated that the suggested alternate approach to account for
inhalation and ingestion exposures (via the RfD and RfC equation)
regardless of the target organ/endpoint was inconsistent with EPA's
guidance on the use of hazard indices (HIs) and hazard quotients (HQs)
to evaluate multiple noncarcinogenic toxicants. Commenters also
questioned whether all exposure routes exhibit the same toxicity or
stated that inhalation exposures should be disregarded if the pollutant
in question does not affect the same endpoint.
Response--Assuming that all multiple exposures from multiple
chemicals are additive, as the commenters suggest, is not
scientifically sound unless they exhibit the same toxic endpoints and
modes of action. We are aware of the complex issues and implications of
cumulative risk and are developing an overall approach at the Agency-
wide level. In particular, the Agency's program offices are engaged in
ongoing discussions on how to address the great complexities,
methodological challenges, data adequacy needs, and other information
gaps, as well as the science policy and risk management decisions that
will need to be made, as we pursue developing a sound strategy and,
eventually, specific guidance for addressing cumulative risks. As
previously indicated, the Agency is developing a framework for
cumulative risk assessment, and the Office of Pesticide Programs has
developed draft guidance for assessing cumulative risk of common
mechanism pesticides and other substances. We have added discussion
about the concept of cumulative risk and the state of the science in
the 2000 Human Health Methodology and its TSDs. As a matter of internal
policy, we are committed to refining the Methodology as advances in
relevant aspects of the science improve. Regarding the alternate
approach to use the HI/HQ equation (combining RfDs and RfCs), we do not
intend to use this approach to combine chemicals when deriving criteria
at this time. We requested comment on this as an alternate method to
consider inhalation exposures for a given chemical, but would not
consider its use in situations where existing information indicates
that ingestion exposures and inhalation exposures affect different
target organs. EPA intends to consider the comparative toxicity between
exposure routes for Section 304(a) water quality criteria and has
encouraged States and Tribes to do so. For the recommended national
304(a) criteria, cumulative risk approaches will not work since the
mixture of pollutants present in water is inherently site-specific.
6. Uncertainty with the Derivation of 304(a) Criteria
Comment--Comments suggested that cumulative uncertainty guidance
should be included in the Methodology, including a maximum acceptable
uncertainty level.
Response--Establishing a maximum level of acceptable uncertainty is
not part of the Methodology and will not be
[[Page 66459]]
factored into the decision of whether to develop or revise 304(a)
criteria. However, issues regarding uncertainties with the risk
assessments, exposure assessments, and bioaccumulation assessments will
be addressed in the risk characterization sections of future criteria
documents.
7. Toxicity Equivalency Factors (TEFs) for Dioxin-like Compounds
Comments--Several commenters addressed the use of TEFs for dioxin-
like and other mixtures and classes of compounds. They believed the TEF
approach has only limited application in risk assessment. Commenters
indicated that complexities of the biology argue strongly against any
more than limited and very cautious use of the TEF approach for
assessment of human health from exposure to dioxin-like compounds.
Response--EPA agrees that there is a limitation to TEF use and that
caution should be exercised when using it. More guidance can be found
in the Guidance for Conducting Health Risk Assessment of Chemical
Mixtures (USEPA, 1999b) and the Health Assessment for 2,3,7,8-
Tetrachlorodibenzo-p-dioxin (TCDD) and Related Compounds, Internal
Review Draft, February 14, 2000; Part II, Chapter 9: Toxicity
Equivalency Factors (TEFs) for Dioxin and Related Compounds (USEPA,
2000b).
C. Cancer
1. Acceptable Risk Level for Carcinogens
Comments--Comments were received suggesting that regulations should
be tightened or that AWQC for all carcinogens including the Groups C
compounds (possible human carcinogens) should be set at zero, while
others believed that cancer potency factors may overestimate actual
risk. Some suggested the actual risk may be much lower, perhaps as low
as zero, particularly for chemicals for which human carcinogenicity
information is lacking. Comments also addressed the EPA cancer risk
range for deriving AWQC.
Response--Regarding the permissible cancer risk range, see response
to Comment A.3, Cancer Risk Range.
2. ED10 (central estimate) versus LED10 (lower bound on dose)
Comments--Several commenters preferred the use of ED10 over LED10
as the POD or BMD.
Response--The 1999 draft revised cancer guidelines provided a
rationale for the selection of PODs. EPA's 1999 draft revisions provide
for the use of the LED10. The EPA Science Advisory Board (SAB) suggests
harmonization of the LED10 between the BMD approach for noncancer
assessments and cancer assessments. The SAB also recommends reporting
both the LED and ED (see USEPA, 1999d).
3. Group C Contaminants
Comments--One commenter stated that Group C compounds are treated
differently under the SDWA and the CWA and wanted clarification on
development of AWQC for Group C contaminants. Also, an ``integrated
approach'' was suggested in evaluating nonlinear carcinogen and
noncarcinogen assessments. However, the commenter's approach was to
determine tentative AWQC for the contaminant as both a noncarcinogen
and a carcinogen at 10-\6\ risk, and then choose the lower
of the two values (i.e., RfD vs. 10-\6\ risk) for setting
the AWQC. Another commenter stated that integrating nonlinear and
noncarcinogen assessments proposed by EPA is reasonable and it may be
possible to replace this in the future with the categorical regression
approach.
Response--The 1999 draft revised cancer guidelines require risk
assessors to use the best science and consider mode of action in
selecting an appropriate model to use. Under the 1999 draft revised
cancer guidelines, Group C will no longer exist. The linear approach is
used when there is insufficient information on mode of action, or the
mode-of-action information indicates that the dose-response curve at
the low dose is or is expected to be linear. The default approach for
nonlinearity is to use a margin of exposure analysis. However, when the
mode of action suggests both linear and nonlinear approaches, then both
methods will be applied and considered. As for the integrated approach,
EPA currently is working to increase the harmonization of both cancer
and noncancer risk assessments. In the 2000 Human Health Methodology,
we will only quantify cancer risks for those chemicals considered
``carcinogenic to humans'' or ``likely to be carcinogenic to humans.''
4. Guidance on Carcinogen Risk Assessment
Comments--Several commenters supported EPA's 1996 proposed cancer
guidelines. They endorsed the proposed guidelines for considering all
scientific data and using the latest information, including weight of
evidence, mode of action, margin of exposure, and a nonlinear approach
for certain contaminants. They thought the new approach is more in line
with recent advances in understanding carcinogenesis. However, they
requested more guidance on how and when to apply the cancer guidelines.
Response--We will provide more guidance when the guidelines are
finalized.
5. Hexachlorobutadiene (HCBD)
Comments--Comments stated that EPA should not propose AWQC for HCBD
before the 1999 draft revised cancer guidelines are final. Furthermore,
for HCBD, there is inconsistency between the statement in the 1998
Federal Register (Appendix VI) and that in the example HCBD criteria
document.
Response--The Agency is considering the comment and will postpone
completion of the AWQC for HCBD until more recent data can be
incorporated. In reference to the risk assessment of the chemical, the
discrepancy is minor. The 1998 Methodology states that both linear and
nonlinear approaches will be used by EPA. The criteria document
presents both approaches.
Note: EPA also will postpone completion of the criteria for 1,3-
dichloropropene. Because of the large volume of new scientific
information available for acrylonitrile, additional effort will be
necessary to review the material. Therefore, EPA will not complete
the criterion for acrylonitrile at this time. For the same reason,
we are not addressing the comments on this chemical at the present
time.
6. Integration of Analyses for Cancer and Noncancer Effects
Comments--Commenters supported integration and harmonizing
procedures for risk assessment of cancer and noncancer effects in
ambient water and drinking water programs.
Response--EPA agrees that it is a good idea to use an integrated
approach to assess both cancer and noncancer effects. Currently, EPA
has Agency-wide efforts to investigate harmonization of cancer and
noncancer risk assessments.
7. Margin of Exposure (MOE) Analysis
Comments--Commenters requested that EPA provide more guidance on
how to do MOE analysis and how to select the MOE. They also requested a
comparison of the BMD with the LED10.
Response--Guidance will be provided either in the final Guidelines
for Carcinogen Risk Assessment or in a separate document from the
Agency's Risk Assessment Forum in the future.
[[Page 66460]]
8. MOE Approach to Applying Uncertainty Factors (UFs)
Comments--A commenter disagreed with the proposal to apply a UF to
account for the severity of a precursor effect. Another commenter
opposed applying a UF of no less than 0.1 when humans are less
sensitive than animals.
Response--The Agency will develop more specific guidance on the MOE
approach, as recommended by the SAB in 1999. The guidance will be peer
reviewed and published separately as part of the Agency's
implementation activity for these guidelines.
9. MOE and MOP
Comments--Commenters seemed confused regarding MOE and MOP
(``margin of protection,'' as defined by a commenter). They defined MOE
= MOP = POD/RfD and claimed that the calculated MOEs for chemicals
based on nonlinear low-dose extrapolation are 100 times higher than
those for carcinogens based on linear low-dose extrapolation, and
claimed that the MOE is implicitly linear and, thus, is an inadequate
approach to dealing with ``nonlinear'' carcinogens.
Response--There is a significant misunderstanding on the part of
the commenters. The MOE is defined as the POD (i.e., NOAEL or LOAEL or
LED10) divided by the environmental level of interest (actual exposure
or possible criterion). The MOE approach is recommended for chemicals
that have a nonlinear low-dose response. For carcinogens with a linear
low-dose response, we estimate the slope of the line drawn between zero
and the LED10, and use the equation presented in the Methodology to
estimate the concentration in water for human heath protection
(10-6 is the recommended risk level). EPA does not recommend
using any formula such as the one presented [i.e., MOE = (POD) /(RfD)]
to estimate MOE for carcinogens with a linear low-dose response.
10. Oral Scaling Factor for Dose Adjustment
Comments--Several commenters endorsed EPA's use of the body weight
raised to the three-quarters power as the scaling factor. It was also
suggested that, if available, chemical-specific data should take
precedence over the generic default scaling factor.
Response--EPA agrees.
11. Toxic Endpoints
Comments--A commenter stated that EPA should make clear in its
Methodology that it intends to take into consideration the toxic
actions of the individual chemicals for which criteria are being
established so that an appropriate target population and consumption
rate can be selected. The commenter suggested that if the critical
toxic endpoint of a chemical is cancer or other chronic disease, then
use of the adult population and long-term consumption rates are
appropriate to develop the AWQC. However, if the most sensitive toxic
endpoint of a chemical of interest is acute reproductive effects, it
may be more appropriate to use short-term consumption rates and
exposure parameters that are relevant for women of childbearing age in
developing the AWQC.
Response--EPA agrees.
12. Weight-of-Evidence Narrative and Classification System
Comments--A commenter expressed support for the use of narrative
statements, but found the guidance on the weight-of-evidence narrative
to be overly general and confusing. They suggested that some sort of
classification system such as the alphanumeric should be retained. They
also stated that without such a system, practical use of the weight-of-
evidence approach will be more difficult, particularly for States that
do not have strong expertise and sufficient resources in the
application of health-based risk assessment.
Response--Current revisions to the cancer guidelines and the use of
descriptors and narratives have been endorsed by the SAB and other
commenters and will be included in assessments and final guidelines
because they provide important information to the risk manager that a
number or letter cannot convey.
D. Noncancer
1. Benchmark Dose Methodology
Comments--Commenters supported the flexibility of having the NOAEL/
LOAEL/UF, categorical regression, and benchmark options for derivation
of an RfD but pointed out a variety of concerns or factors for EPA to
consider as it revises the BMD guidance.
Commenters suggested that the BMD methodology will eventually have
a prominent role in risk assessment, but checks and balances need to be
set to ensure that it is applied intelligently and with a healthy
scepticism for its results, especially those that vary significantly
from the results of the conventional NOAEL/LOAEL approach. The
following specific recommendations were presented for EPA's
consideration:
Prohibit extrapolations without some mechanistic
foundation. Permit interpolation only within the experimental dose
range, for example, between NOAELS and LOAELS.
Present a range of BMD estimates from the use of multiple-
dose models, including models with thresholds just below LOAELS;
estimates with the high-dose results dropped sequentially from the
analysis; and multiple response rates (i.e., 1%, 5%, and 10% response
rates as well as the response rate associated with the experimental
detection limit).
Estimate the BMD using several confidence bounds.
Compare the results of the alternative modeling approaches
and reconcile discrepancies.
Other comments are summarized in the following paragraphs.
The BMD methodology lacks a mechanistic basis. There is no
connection between the mechanisms of action that underlie the observed
responses. Because the methodology is devoid of a mechanistic basis,
its use needs to be restricted to the observable range. Extrapolations
below the lowest nonzero dose of a study have no scientific foundation.
However, it is acknowledged that some extrapolation of the data below
the observable range is inevitable.
An additional critique was that high-dose effects influence low-
dose estimates. The curve fitting involved in estimation of the
mathematical dose-response relationship permits the responses at the
high end of the dose range to influence the estimated responses at the
low end of that range. This will occur whether or not the high-dose
observations are mechanistically related to the responses at low doses.
Furthermore, response and dose estimates are model dependent. In some
cases, both central estimates and lower-bound estimates of doses
associated with various response rates are known to be highly unstable
and fluctuate significantly in response to minor data manipulations or
assumptions.
More research is needed on implementation of the benchmark model.
Guidelines for selecting appropriate models/benchmark responses,
handling lack of fit, or selecting a single benchmark dose when more
than one is calculated should be developed by EPA to assist States and
other users in implementing this methodology.
The central estimate rather than the lower bound on dose should be
used as the POD for benchmark modeling. Such an approach provides
greater opportunity to compare effect doses among chemicals.
Uncertainty associated with wide confidence limits
[[Page 66461]]
can be accommodated in other portions of the risk assessment process.
Furthermore, the most recent peer review of the BMD methodology (USEPA,
1996c) recommended use of the ED10 rather than the LED10.
Use of the benchmark model could introduce additional conservatism
into the derivation of an RfD. Certain benchmark models as applied to
developmental toxicity endpoints are substantially more conservative,
on average, than the corresponding NOAELs. Using the benchmark approach
in such a circumstance will introduce additional unjustified
conservatism in the standard-setting process.
Caution should be taken when using different methods for RfD
determination; that is, the degree of human health protection should be
comparable from different methods. Because the BMD and categorical
regression are relatively new methods, more studies are needed to
compare the RfDs derived using the typical NOAEL/UF approach and those
derived using the BMD and categorical regression methods.
EPA should closely coordinate adopting BMDs for noncancer endpoints
under the Human Health Methodology with other Agency programs so that
the policy is implemented identically throughout the Agency. However,
because the benchmark approach makes better use of all data, the Agency
should continue to work on its development.
Response--EPA agrees with the concerns regarding widespread
application of the benchmark approach without consideration of the many
factors addressed by commenters. The AWQC guidelines do not prescribe
use of the benchmark approach in the derivation of an RfD. The
guidelines allow the use of either the NOAEL/UF, benchmark, or
categorical regression approaches. The risk assessor can select the
approach most suitable to the available data. Accordingly, if the data
do not support derivation of a BMD, then the NOAEL/UF approach can be
selected for the RfD derivation rather than the benchmark approach. In
addition, when selecting the appropriate equation for derivation of the
BMD, one should consider goodness-of-fit along with the impact of high
doses on the model results, confidence interval domains, and
consistency of the dose-response pattern with the mode of action.
We do not anticipate that either of the new approaches, benchmark
or categorical regression, will soon completely replace the NOAEL/UF
approach. Both of the new approaches require more extensive data than
the NOAEL/UF approach, and in many cases the data required to apply the
methodology will not be available.
EPA is developing technical guidance that will assist in
determining whether or not a particular data set is compatible with the
BMD approach. Use of BMD methods involves fitting mathematical models
to dose-response data obtained primarily from toxicology studies. When
considering available models to use for a BMD analysis, it is important
to select the model that best fits the data and is the most
biologically appropriate. EPA has developed software following several
years of research and development, expert peer review, public comment,
subsequent revision and quality assurance testing. The software (BMDS,
Version 1.2) can be downloaded from http://www.epa.gov/ncea/bmds.htm.
BMDS facilitates these operations by providing simple data-management
tools, a comprehensive help manual and online help system, and an easy-
to-use interface to run multiple models on the same dose-response data.
As part of this software package, EPA has endorsed sixteen (16)
different models that are appropriate for the analysis of dichotomous
(quantal) data (Gamma, Logistic, Log-Logistic, Multistage, Probit, Log-
Probit, Quantal-Linear, Quantal-Quadratic, Weibull), continuous data
(Linear, Polynomial, Power, Hill) and nested developmental toxicology
data (NLogistic, NCTR, Rai & Van Ryzin). Results from all models
include a reiteration of the model formula and model run options chosen
by the user, goodness-of-fit information, the BMD, and the estimate of
the lower-bound confidence limit on the benchmark dose (BMDL). Model
results are presented in textual and graphical output files which can
be printed or saved and incorporated into other documents.
2. Categorical Regression
Comments--Commenters expressed reservations regarding use of the
categorical regression methodology. They stated that the methodology
presents difficulties in that it requires distinction of diverse
endpoints and definition of severity categories, not as they apply to
the animal studies, but as they apply to human health effects.
Commenters also stated that categorical regression would allow the
Agency to consider several endpoints simultaneously rather than use
data for only the most sensitive endpoint. Some commenters believed
that the major limitation of the approach is the need for classifying
effects into categories (mild, moderate, frank).
Other commenters believed regression analysis offers attractive
advantages but does not seem well enough developed at the present time
to be incorporated into the Methodology. They suggested that because
the approach makes better use of all data, the Agency should continue
to work on its development. They also stated that when the data
indicate that one of the new methodologies is clearly superior to the
NOAEL/LOAEL/UF approach, it should be utilized.
Response--As stated in the response on BMD above, EPA does not
anticipate that either of the new approaches, benchmark or categorical
regression, will soon replace the NOAEL/UF approach. Both new
approaches require more extensive data than the NOAEL/UF approach, and
in many cases the data required by the methodology will not be
available. We agree that the categorical regression methodology is less
well developed than the benchmark method. However, we also anticipate
that the number of chemicals evaluated with this approach will grow
over time. Including the categorical regression methodology among the
available options in the 2000 Human Health Methodology provides an
opportunity for its application in appropriate situations.
3. Integrated Approach
Comments--Commenters stated that an integrated approach to
assessing both cancer and noncancer effects for substances that are
carcinogenic has merit, particularly when the systemic effects of
concern occur at very low doses. However, they believed it is unclear
how the nonlinear cancer assessment and the noncancer assessment would
differ if the tumors were considered secondary to the systemic toxicity
upon which the RfD is based. They stated that such considerations
become more important when the systemic toxicity is unrelated to tumor
formation, as in the case of lead and mercury. Some indicated that
because EPA recommends different design flows to account for exposure
scenarios that are appropriate for carcinogenic and systemic effects,
the Methodology should develop and adopt similar criteria for both
carcinogenic and systemic effects when appropriate. Some further stated
that for some waters and pollutants, it will not become clear whether
the systemic or carcinogenic criterion is more protective until the
limits are developed using the different design flows. This was not
previously a concern because a single human health design flow was used
in most locales.
[[Page 66462]]
Response--The 2000 Human Health Methodology is not a stand-alone
methodology. It depends on established or proposed Agency risk
assessment guidelines for cancer and noncancer endpoints. We do not
have the latitude to change Agency-wide risk assessment guidelines
through the AWQC Methodology. Any changes must first be made to the
supporting documents (e.g., 1999 draft revised cancer guidelines, RfD
methodology).
4. Integrated Risk Information System (IRIS)
Comments--Concern was expressed that EPA does not update the IRIS
files in a timely manner. States use these assessments for their risk
assessment work and do not have the resources to perform the types of
detailed consensus risk assessment done under the IRIS process,
according to comments received. They additionally pointed out that many
IRIS assessments are more than 10 years old and suggested that EPA
should update these assessments on a 3- to 5-year cycle.
Response--We realize the importance of the IRIS program and
dedicate a portion of our resources to preparation of IRIS
documentation for regulated chemicals. However, competing priorities
throughout the Agency limit the effort that can be expended on IRIS by
program offices and by the IRIS program.
5. NOAEL/LOAEL Approach
Comment--A commenter called attention to the facts that the NOAEL/
LOAEL/UF approach is the current approach for establishing an RfD and
that many present regulatory values are based on this approach. They
stated that use of newer techniques that account for severity of
effects and sample size seems reasonable, as long as the new techniques
have been extensively reviewed and have wide acceptability among
practitioners. However, the commenter also said that in some cases, the
data needed to use the newer techniques may not be available, in which
case it seems entirely appropriate to use the NOAEL/LOAEL approach as a
default.
Response--See our responses to Comments D.1 and D.2, the benchmark
dose and categorical regression comments, respectively.
6. Nonthreshold Approach for Noncarcinogens
Comments--The Agency requested comments on the suitability of using
a nonthreshold approach for noncancer endpoints. Although open to the
concept, commenters stated that a threshold should be considered the
norm and a nonthreshold approach should be applied only if there are
substantial scientific data supportive of a nonthreshold mechanism of
toxicity. They stated that when receptor interactions are a component
of the response, it is important that EPA differentiate between the
receptor binding that might be without a threshold and subsequent
biological responses such as enzyme induction or frank toxicity that
would be expected to exhibit threshold dose-response relationships.
An additional concern was the use of nickel as an example of a
chemical without a threshold. It was pointed out that double-blind
studies indicate that there is a threshold for dermatological responses
to nickel even in sensitized individuals.
Response--The Agency made modifications to the recommendations
regarding a threshold approach for noncarcinogens, most specifically
using lead as an example rather than nickel. We incorporated the
commenters' suggestions in making the revisions.
7. RfD Range
Comments--The concept of establishing a range around the calculated
RfD from which an alternative RfD might be selected in certain
circumstances received considerable comment from the public. The
primary criticism was the lack of a scientific basis for the breadth of
the range and its correlation to the net uncertainty factor/modifying
factor (UF/MF) product. The comments are summarized below.
The span of the range as described by EPA seems to be arbitrary and
without any scientific support. It would be useful for the Agency to
analyze a substantial number of past RfD determinations using the
ranges the Agency has proposed to see whether they make practical
sense. The Agency should provide more examples on how the factors that
are to be considered in selecting a point within the range (i.e.,
bioavailability differences, sensitive populations, and slope of the
dose-response curve) are related to the magnitude of the proposed
range. Scientific data should be gathered and presented to support the
use of these factors in influencing the range.
The Agency should give serious consideration to the possibility
that the ranges of uncertainty surrounding the point estimate are not
symmetrical. In particular cases, it may well be that most of the RfD
uncertainty is on the high side of the point estimate.
The proposal to use a range is inconsistent with the purpose of the
RfD. The proposal to use a range rather than a point value for the RfD
would lead to the potential for double counting uncertainty. The UFs
and MFs presently applied in calculation of the RfD allow for many of
the factors that are presented as justifying selection of a point
within a range as an alternative to the calculated RfD.
The range for the RfD would create more problems than it would
prevent. The RfD, by nature, cannot be used to calculate the risk at a
given level of exposure and is essentially a safety estimate that
should be expressed as a single point estimate. The definition of the
RfD recognizes the uncertainty in this assessment. The proposed
approach would be difficult to implement, create unnecessary confusion
and controversy regarding the RfD, and could result in prolonged
unproductive debates between parties with differing interests.
If EPA chooses to define a range, the range should be developed by
the scientists undertaking the RfD development. If a range is used, it
is also strongly recommended that it be accompanied by detailed
guidance on the factors for choosing a point estimate within the range.
The uncertainty surrounding the point estimate of an RfD will be
different for each chemical and study and should be clearly stated in
any revised RfD.
An advantage of the range is that it would make more apparent to
States the uncertainty in the RfD and the flexibility that now exists
surrounding its use in the regulatory context. However, it is
preferable to retain the presentation as a single point value but
provide in accompanying text substance-specific information such as
steepness of the dose-response curve that States can use in deriving
standards based on other than the default single point RfD.
A range is useful to a risk manager or other decision-maker because
actions can be taken with greater confidence in how likely it is that
adverse health effects will be manifest at a particular point
concentration. For example, slightly exceeding the MCL of 1 mg/L for
nitrite with a UF of 1 is more likely to result in adverse health
effects upon exposure than slightly exceeding a guideline of 70
g/L for MTBE with a UF of 10,000.
Some of the factors EPA recommends in selecting a point within an
RfD range should be used in determining the RfD itself rather than for
deviating from it after it is derived. These include the seriousness
and reversibility of the effect, whether it is based on a LOAEL,
[[Page 66463]]
and bioavailability within humans. The issue of considering the
presence or absence of sensitive segments of the population is
impractical and inappropriate in deriving an ambient water quality
standard. EPA should delete this option and understand that States
generally set water quality standards on a statewide level. It is
impractical to ascertain whether infants or pregnant women live near
and consume fish or water from a particular waterbody. It is not
practical from an administrative standpoint to set different, separate
standards for each waterbody.
The Agency should provide guidance regarding the development of
scientific rationales for departure from the default RfD. The Agency
should provide a methodology for deriving the range, along with
supporting examples, and subject that methodology to peer review before
using the concept in developing AWQC.
Response--EPA agrees that the method used to quantify the range
from which an alternative to the calculated RfD can be chosen is not
based on specific scientific or statistical data. It is purely an equal
partitioning of a default, 10-fold uncertainty factor into four equal
quarter log segments.
It is important to note that the range around the calculated RfD
only establishes a domain from which a risk assessor can select a
single point to use as an alternative to the RfD for a specific
circumstance. The 2000 Human Health Methodology criteria for using a
point within the range other than the calculated RfD when calculating
AWQC clearly require the State to provide a detailed justification for
that decision.
One example of a situation where a point other than the calculated
RfD might be applied would be where there is a difference in the
bioavailability of the contaminant in the water component of the AWQC
as opposed to the fish component. In such an instance, the decreased
bioavailability from fish tissues could be used to support selection of
an alternative value greater than the calculated RfD if the critical
study were one where the contaminant had been administered through
drinking water. Most inorganic contaminants, particularly divalent
cations, have bioavailability values of 20 percent or less from a food
matrix, but are much more available (about 80 percent or higher) from
drinking water. Accordingly, the external dose necessary to produce a
toxic internal dose would likely be higher for a study where the
exposure occurred through the diet rather than the drinking water. As a
result, the RfD from a dietary study would likely be higher than that
for the drinking water study if equivalent external doses were used.
The exposures considered in deriving AWQC include fish (food) and
water. Thus, one might be able to justify an alternative value to the
RfD point estimate that was slightly higher than the RfD estimate in
cases where the NOAEL that was the basis for the RfD came from a
drinking water study, but slightly lower than the RfD estimate if the
NOAEL came from a dietary study.
Several commenters suggested that there would be value in applying
the range concept to several relevant RfD values and then to evaluate
the results. The range concept was considered in the peer review of the
1998 draft Methodology revisions, and the peer reviewers had many of
the same concerns regarding the range. The revised Risk Assessment TSD
gives examples of how one could justify an alternate RfD value that was
lower or higher than the RfD estimate.
8. Severity of Effects
Comments--Several commenters supported consideration of severity of
effects in determining AWQC, although there was considerable diversity
in the opinions expressed, as follows.
Some believed that there was no science behind use of different UFs
(i.e., 3, 10) in making intraspecies decisions based on severity of
effect. Some stated that EPA should provide a methodology that will
define a severity scale prior to adopting use of severity in deriving
RfDs and associated AWQC. Others commented that the severity scale
could be alphanumeric, similar to that used for carcinogens under the
EPA 1986 cancer guidelines, and the severity rating could be presented
along with the RfD value. However, any severity scale must also
consider whether it is consistent with the definition of an RfD as a
dose below which no adverse effects are anticipated to occur in exposed
populations.
Other commenters believed that making adjustments in the RfD value
for severity of effects only confounds regulatory policy with
toxicological science, and the Agency should explore alternative
approaches to the problem of differences in severity of various
toxicological endpoints. The Agency should not have considered severity
in calculating an RfD because this practice could result in double
counting of uncertainty. Severity should be considered in selection of
a UF only when the RfD is based on a LOAEL. If the NOAEL were used,
concerns for severity should be reflected in the MF.
Response--There are several situations in which EPA has considered
the severity of effect in selection of the UF. The Risk Assessment TSD
cites zinc as an example. The LOAEL used in establishing the RfD for
zinc was a change in the activity of the enzyme superoxide dismutase.
This effect compromises the ability of the individual to avoid damage
to macromolecules, such as proteins and polynucleotides, in the
presence of free radical oxygen. Although clearly adverse, this effect
is not as severe as tissue necrosis or impaired organ function. Thus, a
UF of 3 was used rather than the default of 10 for the adjustment of a
LOAEL to a NOAEL. The nutritional requirements for zinc relative to the
RfD supported the use of a UF of less than 10 in this instance.
As monitoring of molecular biomarkers of toxicity increases, the
number of situations will most likely increase in which a LOAEL is
early enough in the progression toward overtly adverse effects that
factors of less than 10 can be used for the RfD calculation and will be
supported by mode of action data. Past EPA practice is consistent with
the suggestion that severity be considered where the RfD is based on a
LOAEL and that an MF be used, if the data warrant, when calculating
from a NOAEL.
We do not believe that establishing a scale for severity is
necessary at this time. It would be extremely difficult to establish a
scale for rating toxicological endpoints that could be easily applied
to the spectrum of endpoints monitored in more recent toxicological
studies. The present flexibility in UFs and MFs provides ample
opportunity for severity adjustment.
9. Stochastic Modeling
Comments--Commenters encouraged EPA to use a stochastic approach
(Monte Carlo and/or Latin square modeling) for setting RfDs. The
commenters stated that this would allow EPA to better ``quantify the
uncertainties and separate them from the variability in the data.''
They believed such methods would provide a sounder, more quantitative
approach to determining whether a range of RfD values is needed.
Response--The guidelines for determination of the RfD are based on
previously published, Agency-wide guidelines. The suggestion to use a
stochastic approach has been noted and will be considered in the
context of the Agency revisions to its risk assessment guidelines.
Revisions to fundamental Agency guidelines are beyond the scope of the
AWQC Methodology.
[[Page 66464]]
10. Synergistic Effects
Comment--Several commenters encouraged the Agency to consider
multiple exposures to various chemicals and persistent bioaccumulative
toxicants when establishing AWQC. For substances that do not persist or
bioaccumulate in the environment, or do not cause reproductive,
developmental, or neurological effects, EPA's risk assessment
methodologies were deemed in need of reconsideration. However, as part
of the reconsideration, EPA was asked to apply best science on
synergistic impacts from exposures to a combination of chemicals. Other
comments suggested sensitive subpopulations, such as Native American
Tribes and other susceptible populations, may have significant
confounding, underlying health problems that must be recognized with
any synergistic assessment.
Commenters also stated that EPA should give specific attention to
certain categories of contaminants: persistent organic pollutants and
endocrine disruptors. The commenters identified two aspects to consider
in applying this recommendation: (1) Individual contaminants with a
similar mode of action whose cumulative effects may reach an
unacceptable level; and (2) selection of specific biologic endpoints to
use as the basis of an RfD. They also believed that tissue effects are
valid measures of injury and should be used in addition to organ-level
effects in people and biota. It was also considered important to
include immunological, reproductive/developmental, and neurological
effects to derive RfDs.
Response--The Risk Assessment TSD encourages States to consider
synergistic and additive effects of individual chemicals in mixtures
when establishing AWQC. The HI approach is suggested and described for
situations where the chemicals have the same effect by similar modes of
action. The Risk Assessment TSD also acknowledges that methods are not
presently available for evaluating risk from mixtures where the
individual chemicals have dissimilar health effects and recommends that
chemicals in such mixtures be evaluated individually. Specific
recommendations are found in EPA's Draft Guidance for Conducting Health
Risk Assessment of Chemical Mixtures published in May 1999 (USEPA,
1999b).
The 2000 Human Health Methodology accommodates concerns regarding
persistent bioaccumulative toxicants primarily through use of
bioaccumulation factors in the calculation. Situations in which ambient
waters may contain a group of chemicals that are persistent and
bioaccumulative and have additive or synergistic effects can in some
cases be factored into the HI approach. The description of the
treatment of mixtures in the TSD was expanded to encourage States to
consider persistence, bioaccumulation, and mixtures concerns in their
risk assessments. The references to Agency mixtures guidelines were
updated to include the most recent draft of the mixtures guidelines.
11. Target Population Adjustments
Comments--EPA was asked to consider the characteristics of the
target population when determining AWQC. Commenters suggested that when
the chemical is a carcinogen, it is appropriate that the target
population consist only of residents of the United States. In cases
where the effect is an acute reproductive effect, the commenters
believed it is appropriate to specify adult women as the target
population and to use short-term consumption rates and exposure
parameters.
Response--The default input parameters for determining AWQC for
human health apply to lifetime exposures and the adult population of
the United States. However, the equations used for the calculation
provide the flexibility to use body weight, water intake, and fish
intake parameter values that are specific to other target populations.
12. Uncertainty and Modifying Factors
Comment--Additional guidance was requested on factors to consider
in selecting UFs, particularly a UF for an incomplete database.
Response--In revisions to the Risk Assessment TSD for the 2000
Human Health Methodology, we increased the number of examples given to
illustrate how UFs were selected in establishing RfDs included in the
IRIS.
Comment--The suggestion was made to replace the interspecies UFs
with a body weight to the three-quarters power and thereby harmonize
the cancer and noncancer approaches.
Response--The peer reviewers of the 1998 draft Methodology
revisions also suggested harmonizing the cancer and noncancer
approaches with regard to the use of the body weight to the three-
quarters power. This can be accomplished only through changes to the
Agency documents on which the methodologies presented in the 2000 Human
Health Methodology are based. The Agency currently is working on
harmonizing the cancer and noncancer methodologies.
In addition, as pointed out by the peer reviewers, a body weight to
the three-quarters power conversion adjusts for allometric differences
between laboratory animals and humans. It does not reflect
toxicodynamic differences between species that must still be included
when adjusting for interspecies differences. The use of the scaling
factor cannot totally replace the interspecies UF.
Comment--Another comment requested EPA to adopt more rigorous
quantitatively supportable methods such as PBPK models to replace the
more arbitrary and less well founded use of numerical scaling factors
identified in UFs and MFs.
Response--The revisions to the Methodology clearly support use of
toxicokinetic modeling when the data are available and use of the
modeled data in lieu of the toxicokinetic portion of the interspecies
UF.
13. Use of Less-Than-90-Day Studies in Determining an RfD
Comments--In general, commenters agreed with the scientific review
board that false-negatives might result from use of less-than-90-day
studies to develop an RfD. It was suggested that EPA evaluate data sets
for groups of chemicals for which there are both chronic and less-than-
90-day studies and compare RfDs. Any comparison of chronic and less-
than-90-day studies should consider the purpose for which the less-
than-90-day studies were conducted and whether they provide evidence
relevant to the results of longer term experiments. A commenter agreed
with the scientific review board that any RfD based on a less-than-90-
day study should be used only temporarily.
Other comments pointed out that the Great Lakes methodology allowed
use of less-than-90-day studies for determining an RfD but required a
duration UF of 30 rather than 10. This factor when combined with a 10
for intraspecies variability and a 10 for interspecies variability
would yield a total UF of 3,000, the maximum that is said to support
RfD derivation. The commenter believed very few situations would
qualify to use less-than-90-day studies, but their use should be
allowed as long as the total UF is 3,000 or less.
Additional comments stated that reproductive, developmental,
immunotoxicological, and neurotoxicity data provide an appropriate
basis for determining an RfD even if they come from studies of less-
than-90-day duration. However, one commenter also urged that data must
be collected using
[[Page 66465]]
methods of sufficient accuracy and validity. It was also emphasized
that evaluations should be conducted to determine how dose-response
relationships developed for these toxic effects, particularly
immunotoxicity, are related to modifications in function and evidence
of overt pathology.
Response--In several instances, the Agency has developed an RfD
based on data from studies of less-than-90-day duration (e.g., nitrite,
zinc), particularly where the data were from humans and evaluated
endpoints of chronic as well as acute significance. Data from less-
than-90-day studies of reproductive, developmental,
immunotoxicological, and neurotoxicity data are also considered
appropriate for an RfD if they identify the critical effect. However,
such data are used for RfD determination only when supported by a
rather complete database and a good understanding of the mode of
action. The Agency does not use data from less-than-90-day studies
purely because they are the only available data. When the database is
inadequate to support an RfD determination, no RfD is calculated.
E. Exposure Assessment
Default Intakes
1. Assumption That All of the Drinking Water Consumed Is Contaminated
at the Criteria Level
Comment--A commenter questioned the assumption that all drinking
water consumed has been contaminated to the maximum extent allowed by
the criteria.
Response--Refer to response on this same issue for Comment E.2,
Assumption That All Fish Consumed Is Contaminated at the Criteria
Level.
2. Assumption That All Fish Consumed Is Contaminated at the Criteria
Level and All Fish May Come from One Waterbody
Comments--Commenters questioned the assumption that all fish
consumed have been contaminated to the maximum extent allowed by the
criteria. They state the assumption that all of the 17.8 g/day (now
17.5 g/day) could come from one source is unrealistic, and that EPA
should specify ways to adjust the fish intake rates to reflect a
contaminated fish consumption rate.
Response--As required under Section 304(a) of the CWA, EPA develops
water quality criteria that reflect the latest scientific knowledge on
effects of pollutants on human health. The Agency's recommended 304(a)
water quality criteria are used by States and authorized Tribes to
adopt enforceable water quality standards including designated uses of
a waterbody consistent with Section 101(a) of the CWA (e.g., fishing,
swimming, propagation of aquatic life, recreation). In developing the
2000 Human Health Methodology, we have made assumptions about exposure
to contamination from eating fish taken from surface waters of the
United States. The purpose of the assumptions is to ensure that if
criteria are met in a waterbody designated with the uses specified in
Section 101(a) of the CWA, fish consumers can safely eat fish from that
waterbody. In addition to the assumption that 17.5 g of fish are
consumed per day based on the most recent U.S. Department of
Agriculture (USDA) survey data (a value reflecting the 90th percentile
of the general population), EPA also assumes that fish and shellfish
are taken from water with pollutants present at the criteria level. In
order to ensure that people can safely eat fish from waters designated
with Section 101(a) uses, it is necessary to assume that all of the
consumed fish is taken from waterbodies at the criteria level (i.e.,
contaminated to the maximum safe level).
We recognize that fishing patterns (i.e., extent and location of
fishing) and the degree to which fish and shellfish bioaccumulate
contaminants from waters across the United States may differ from the
exposure assumptions used to calculate national 304(a) water quality
criteria. However, the degree and frequency of such variation are not
clearly known, and these potential differences do not relieve EPA from
its CWA obligations to develop national water quality criteria (which
States and authorized Tribes may modify) that are protective for the
general population. Furthermore, we note that not all of these
differences would lead to less restrictive (higher) AWQC. For example,
some subpopulations may consume fish at a higher rate than the 17.5 g/
day assumed in the national 304(a) criteria, and bioaccumulation might
occur to a higher degree than the central tendency assumptions used in
calculating the national default BAF. As indicated above, EPA believes
that the data do not exist to enable us to account reliably for the
myriad of spatial and temporal differences in fishing patterns and
bioaccumulation and subsequent differences in exposure to fish
contaminants at the national level. In addition, we have not received
information from any stakeholder that would allow us to make such fine
distinctions. Our goal is to ensure that populations who rely on a
particular waterbody as the predominant source of their fish and
shellfish are adequately protected, thus protecting the designated use
of that waterbody. For these reasons, we believe that these assumptions
are appropriate for the development of 304(a) criteria. Where States
and Tribes have concerns regarding the level of protection afforded by
EPA's national 304(a) criteria, we encourage States and authorized
Tribes to make appropriate adjustments to reflect local conditions
affecting fish consumption and bioaccumulation. Guidance for making
such modifications is provided in the 2000 Human Health Methodology.
3. Body Weight Assumptions
Comments--Numerous comments were submitted on issues regarding the
adequacy of the body weight default values recommended in the 1998
draft Methodology revisions and what age-based body weight categories
are appropriate. Several commenters stated the proposed default body
weights were appropriate and that the 70 kg default for adults is
appropriate. One commenter stated that the difference between 70 kg and
the 65 kg value for women of childbearing age is so small that to
distinguish between the two is unimportant. Another believed that the
recommended children's body weights are sufficient and that finer age
categories would not be useful at this time. However, other commenters
addressed the potential need to use finer age-category body weights if
it is known that the adverse health endpoint affects a particular age
group sensitive at that developmental stage, and one commenter stated
that the broad-age default (i.e., for 0- to 14-year-olds) would be
inappropriate for an infant. Another commenter pointed out that the
default assumption for children ages 1 to 3 (i.e., 10 kg) is too low
compared with data from EPA's Exposure Factors Handbook. Other comments
advocated that EPA specifically define the percentile value associated
with the defaults or recommended that EPA not specify default body
weights for children.
Response--We believe it is useful to provide default parameters for
various population groups of concern, where possible, and have received
support for this from States and from the recent peer review workshop
panel. The difference between the general adult default body weight and
the weight for women of childbearing age is statistically significant
and, therefore, we are providing this value for situations where the
critical health endpoint is an in utero developmental effect. All
parameters used for an exposure evaluation should reflect the specific
population group of concern.
[[Page 66466]]
As stated in the 1998 draft Methodology revisions, EPA has not provided
finer age group defaults for children because the fish intake data do
not permit breakouts other than the broader age category. However, in
spite of this limitation, we have included finer age group body weights
for State and Tribal use (when they have local or regional fish intake
data that allow for their use) in the Exposure Assessment TSD. In most
cases, we have indicated the specific percentile from each data source
for the default value chosen (based on the surveys used and not in the
context of the total population because data are not available to
conclusively describe the entire population), but we have clarified
this in the 2000 Human Health Methodology. Associating a derived
criterion with a specific percentile is not possible because such a
quantitative descriptor would require more detailed distributional
exposure and dose information than is available.
EPA acknowledges that the proposed value of 10 kg for a child ages
1 to 3 is lower than the values reported in the Exposure Factors
Handbook (USEPA, 1997a). The 2000 Human Health Methodology uses default
body weight values based on the more recent NHANES III data. Contrary
to the one commenter's suggestion, the data were not chosen to
overestimate exposures; we intended to choose the average body weight
as a default. In all cases (i.e., for the adult, childbearing woman,
children aged one to ten, and infant/toddler categories), we chose
average (mean) body weight values as defaults and do not believe these
are overly conservative.
4. Combining Consumption Intakes and Body Weights
Comments--Several commenters stated that when possible or where
appropriate, the intake values and body weight data should be combined
to generate a ratio/correlation of consumption to body weight, in order
to provide better estimates. One commenter requested that EPA consider
deriving a 95th percentile value of the water consumption to body
weight ratio as the basis for the national 304(a) criteria. However,
the opposite opinion was also expressed; that is, several commenters
supported the use of separate parameters in the derivation equation.
One commenter stated that, based on mean intake and body weight rates
in EPA's Exposure Factors Handbook, differences in fish and water
intakes between pregnant women and adults in general are so
insignificant that they are not worth distinguishing. Opinion was also
expressed that differences in intake rates per unit body weight can be
more significant for children. EPA was cautioned to make sure that if
differences in body weight are considered for different age groups,
then the variation of intake by each specific group also needs to be
considered.
Response--EPA agrees that the intake rates and body weights for the
specific population groups should match (e.g., a body weight for women
of childbearing age should be matched with a drinking water intake
assumption for women of childbearing age). However, we believe that the
exposure parameter choices should be based on the population of
concern, regardless of how small the change in the resulting criterion
might be compared with a general adult population default. We also
believe that there is not always a direct relationship between
consumption and body weight. When EPA presented the issue for review by
the Agency's SAB, they provided the following advice:
In theory it would be better to develop standards on a per
kilogram body weight basis. However, in practice the results are not
different enough to make much difference in the magnitude of AWQCs.
In particular, data should not be rejected because individual body
weights are not available, and funds should not be allocated for
collecting such data since no conceivable benefit would accrue.
EPA has also received input from its State stakeholders regarding
potential confusion over combining the two parameters. Most believe
that the difference in accuracy is negligible but that the difficulty
in associating the units of mg/kg-BW/day with a meal size, especially
for public communication and understanding, is great and, therefore,
not particularly useful. Several stakeholders believed that if the data
were combined as part of a study, or if a strong, demonstrated
correlation between intake and body weight exists, the combined
parameter should be used. We have evaluated recent information on both
drinking water intake and fish intake from the 1994 to 1996 CSFII data
and have assessed the differences between the two units of measure--
including an emphasis on the differences that result with smaller age
categories and drinking water consumption rates for children when mL/
kg-BW/day are used (USEPA 2000c,d). [Note: SAB's comment on the
unavailability of individual body weights is not an issue with the
CSFII; that is, this information is available.] EPA intends to base its
national 304(a) criteria on the separate intake values and body weights
because of the strong input received from its State stakeholders.
However, we have also provided tables in the final Exposure Assessment
TSD of all fish/population categories for both g/day and mg/kg-BW/day,
if States or Tribes prefer their use. The TSD will also provide
examples on deriving criteria using either, including identifying
situations where the latter estimate may provide substantively more
accurate estimates. Additionally, the TSD will provide tables listing
comparable values in mg/kg-BW/day (fish) or mL/kg-BW/day (drinking
water).
5. Combining Fish Intake and Body Weights
Comments--Several commenters recommended the use of separate fish
intake and body weight assumptions because of clarity, familiarity
among the States, and data availability. Specifically, the option of
combining these values was not considered practical because most
studies do not provide such information, even if potentially more
accurate. Furthermore, it was suggested that this complicates the
derivation process or introduces error (an example was cited), and
States and Tribes have the flexibility to use intake values other than
the default values provided. Another commenter stated that there is a
direct proportional relationship between fish consumption and body
weight and that selection of the 90th to 95th percentile value of fish
consumption per unit body weight is an appropriate basis for deriving
the criteria.
Response--EPA agrees that the use of separate fish intakes and body
weights is more easily understood and provides reasonable and
protective default estimates. For additional discussion, see our
response to Comment E.4, Combining Consumption Intakes and Body
Weights. We do not agree that there is necessarily a direct
relationship between fish intake and body weight, especially in the
context of intake on a per-unit-body-weight basis.
6. Default Drinking Water Intake Rates
Comments--One commenter stated that EPA has overestimated the
amount of untreated surface water consumed by the population. However,
another commenter believed that the 2 L/day rate is reasonable. A
commenter stated that drinking water intake rates in hot, arid climates
may be higher than the recommended default rate. Numerous commenters
stated that incidental water ingestion should not be considered in
deriving AWQC or that it is unimportant. One called for empirical data
to support its use and believed that
[[Page 66467]]
EPA has implied that incidental ingestion occurs every day. However,
other commenters believed that this route should be considered for
waters not designated as drinking water sources. One of these requested
that EPA provide additional guidance on incidental ingestion relevant
to acute toxicity and exposures. Another recommended that EPA evaluate
the circumstances to determine whether the incidental ingestion rate
would make a difference. A commenter recommended that EPA use a 30 mL/
hour assumption in cases where short-term effects may be considered in
criteria derivation. One commenter stated that the 10 mL/day value
would be too restrictive for use in all nonpotable waterbodies and
would conflict with existing State guidance on incidental ingestion.
Response--EPA acknowledges that much of the population consumes
water from public water supplies that receive treatment. However, we
intend to continue including the drinking water exposure pathway in
deriving AWQC for the reasons clearly stated in the 1998 draft
Methodology revisions. Refer to that discussion for clarification on
this issue [see Federal Register Notice, August 14, 1998; Appendix III,
C.1.(b)]. We encourage States and Tribes to use alternative intake
rates if they believe that water consumption is higher in arid climates
than the recommended default rate. We have not assumed that incidental
ingestion occurs every day. We have estimated an averaged rate based on
available study information. When initiating the process to revise the
methodology, several stakeholders identified recreational or accidental
water ingestion as a potential health concern. A couple of States have
indicated that they already have established incidental ingestion rates
for use in developing water quality criteria. EPA agrees that the
averaged amount is negligible and will not have any impact on the
chemical criteria values representative of both water and fish
ingestion. The lack of impact would likely also be true for chemical
criteria based on fish consumption only, unless the chemical exhibits
no bioaccumulation potential. However, we believe that the issue could
be important for the development of microbial contaminant water quality
criteria, and for either chemical or microbial criteria for States
where recreational uses such as swimming and boating are substantially
higher than a national average would indicate. Although we will not use
the incidental ingestion intake parameter when deriving our 304(a)
national chemical criteria, we will leave the guidance language in the
final Exposure Assessment TSD in order to assist States and authorized
Tribes that face situations where this intake parameter would be of
significance.
7. Default Fish Intake Rates
Comments--EPA received strong support for its hierarchy of
preferences regarding fish intake values; that is, use of local or
regional studies, and studies characterizing similar populations and/or
geography, over default values. EPA also received support for
encouraging decisions on intake rates to be made at the State or Tribal
level. EPA generally received support for its default fish consumption
rates, including the national 304(a) criteria value of 17.8 g/day (now
17.5 g/day based on the 1994-96 CSFII data). There was support for the
new default rates as more accurately representing current levels of
fish consumption among the general population than the old assumption
of 6.5 g/day. Support was also received for providing the variety of
default values to protect highly sensitive or highly exposed population
groups. One commenter advocated that EPA clearly state that using the
90th percentile value is a risk management decision. However, others
stated that EPA has overestimated fish consumption for the population
at large. A commenter stated that EPA should use the intake value that
its Superfund program utilizes (i.e., 54 g/day). EPA also received
support for the default of 86.3 g/day for subsistence fishers (now
142.4 g/day based on the most recent USDA survey data). Some commenters
disagreed with the use of a subsistence default as contrary to the
purpose of AWQC (while conceding its use for site- or region-specific
criteria) or recommended that EPA caution against the use of
subsistence values without risk management decisions balancing risk
benefits and costs. One commenter stated that subsistence populations
are very rare and cannot generally be defined by socioeconomic factors
and, thus, EPA's assumption of 86.3 g/day may be over-or
underprotective. Several commenters stated their support for the
subsistence default but also advocated that EPA should require States
to consult with Tribes in order to select an adequate fish consumption
rate. Other comments expressed the opinion that a Tribe would be
obligated to use EPA's default value if the Tribe could not conduct its
own survey or expressed concern over the extrapolation of data from the
general population to subsistence populations. Several commenters
questioned EPA's choice in selecting a value to represent the 90th
percentile of the general population, in contrast to selecting average
values for sportfishers and subsistence fishers. A commenter stated
that the assumption of 17.8 g/day as a default for sport anglers was
not supported by peer-reviewed studies and contradicts the EPA's
Exposure Factors Handbook. Another commented that because 17.8 g/day is
recommended to represent the general population, it should not be used
to represent sportfishers and indicated that 39 g/day may be more
appropriate. Other comments advocated the use of actual sportfisher/
subsistence population data or making sure that the defaults chosen
appropriately correspond to these groups.
Two commenters stated that the recommended values for children and
women of childbearing age were overly conservative and inappropriate
because developmental effects would not result from short-term
exposures. However, another commenter stated that evidence on
reproductive/developmental effects should make EPA take the most
conservative approach to protect pregnant women, fetuses, and young
children. Other commenters found these values acceptable and believed
that the approach is consistent with EPA developmental toxicity
guidelines. One commenter noted that single meal or short-term
consumption for these groups could easily exceed the EPA defaults.
Other comments cautioned EPA to make sure that the exposure assumptions
to protect against developmental health effects be used only with
chemicals causing acute toxicity, or believed the defaults are
unrealistically high and favored an averaged daily equivalent (mean or
median value). Two commenters believed that basing both national and
regional criteria on a fish consumption rate in the 90th to 95th
percentile would be most appropriate, and one stated that the high-end
percentile should be used with rates for children and women of
childbearing age to protect against reproductive or developmental
effects. Another commented that criteria to protect subsistence fishers
or pregnant women should be left to the States and Tribes to consider.
Still another suggested that EPA develop special fish consumption rates
for populations that consume much higher amounts than average and,
thus, not be overly conservative in its default assumptions. Two
commenters questioned EPA's assumption that children consume more fish
on a body weight basis than adults, and one commenter advocated use of
childhood fish consumption rates. Concern was also expressed that all
of
[[Page 66468]]
the default rates assume that consumers eat from a single source only,
and that the RSC factor results in a double-counting of fish intake
rates. One commenter said that EPA should not establish default values.
Finally, one commenter advocated using mean consumption rates (not the
90th percentile) if the Agency intends on retaining its RSC factor.
Response--EPA acknowledges the support for the default fish intake
rates. Our national 304(a) water quality criteria serve as guidance to
States and authorized Tribes, who must in turn adopt legally
enforceable water quality criteria into water quality standards. States
and authorized Tribes have the option to develop their own criteria and
the flexibility to base those criteria on population groups that they
determine to be at potentially greater risk because of higher
exposures, yet, EPA cannot oblige the States to specific consulting
agreements because, again, criteria are guidance, not enforceable
regulations, and do not impose legally binding requirements. Therefore,
we recommend that States and Tribes give priority to identifying and
adequately protecting their most highly exposed population by adopting
more stringent criteria, if the State or Tribe determines that the
highly exposed populations would not be adequately protected by
criteria based on the general population. In all cases, States and
authorized Tribes have the flexibility to use local or regional data
that they believe to be more indicative of the population's fish
consumption--instead of EPA's default rates--and we strongly encourage
the use of these data. In most instances, using alternate fish intake
rates should not be difficult, once the value has been determined, in
that the criteria calculation is performed by substituting the State/
Tribal intake rate in place of EPA's default rate. We believe that the
assumption of 17.5 g/day (again, based on the recent 1994-96 CSFII
data) will protect a majority of the population of consumers of fresh/
estuarine finfish and shellfish, especially population groups who rely
on a particular waterbody for most or all of their fresh/estuarine
intake. It is our goal to utilize an intake rate that represents more
of the population than would a central tendency value. Thus, we intend
to derive our national 304(a) criteria using this 90th percentile
assumption, based on the updated analysis of the 1994-96 CSFII data.
EPA also acknowledges that other Agency programs may utilize different
default assumptions. In the case of the Superfund program, the value
used (54 g/day) represents a default used for recreational fishers. It
reflects total fish consumption from both marine and fresh/estuarine
sources; however, it includes only finfish, not shellfish. As such, it
cannot be directly compared to our default based on the general
population for finfish and shellfish from fresh/estuarine sources only.
[Note: The comparable 90th percentile CSFII value from the 1994-96
data, if marine species were included, would be 74.87 g/day.] For the
AWQC program, EPA believes it has selected an appropriate, not overly
conservative default value, given the goals of the CWA and the criteria
program.
For the rationale stated above, we strongly believe that providing
a default rate for subsistence fishers is important for States and
Tribes, if they choose to use it in lieu of their own study data. We
disagree with the commenter that the concept is contrary to the purpose
of AWQC. Moreover, the commenter appears to have incorrectly assumed
that EPA would base its national 304(a) water quality criteria on the
subsistence fishers intake value. We intend to base our national
criteria on the recommended value for the general population. We
emphasized in our 1998 draft Methodology revisions that States and
Tribes should consider developing criteria based on highly exposed
populations when those populations would not be adequately protected by
criteria based on the general population. This is, in fact, consistent
with the purpose of AWQC. We also acknowledge that there is variation
in fish consumption patterns, especially among subsistence fishers. For
the purpose of providing one national intake rate for subsistence
fishers, we believe that the value of 142.4 g/day (an estimated
national average value based on comparing the CSFII 1994-96 data with
subsistence fisher studies) is appropriate. Although the exact
percentile represented by the arithmetic mean varies from survey to
survey, we believe this value is more appropriate and protective than a
median or central tendency value--which we cautioned against using in
the 1998 draft Methodology revisions, because median values in the
available short-duration surveys may be zero. However, as indicated
above, EPA strongly encourages the use of site or regional-specific
studies instead of this default value, and the State's/Tribe's
discretion in considering higher intake rates than an arithmetic mean.
We reemphasize here our four-preference hierarchy, which is designed to
give States and Tribes more options than simply conducting a survey or
using our default. EPA's national 304(a) criteria are health-based
values only and are not intended to account for cost/benefit analyses.
As indicated in our 1998 draft Methodology revisions, risk management
decisions regarding balancing risk benefits should be made at the State
or Tribal level.
EPA believes it is appropriate to offer default fish intake rates
for children and women of childbearing age for States and authorized
Tribes to consider if exposures resulting in health effects in children
or developmental effects in fetuses are of primary concern. We have
recommended a 90th percentile from the 1994-96 CSFII for this potential
situation, in order to protect a majority of these population groups.
As stated in the 1998 draft Methodology revisions, EPA is not
recommending the development of additional water quality criteria,
similar to the drinking water health advisories, which focus on acute
or short-term effects because these are not seen routinely as having a
meaningful role in the water quality standards program. However, we
disagree with the commenter that developmental effects cannot result
from short-term exposures. To the contrary, we believe there may be
instances where the consideration of acute or subchronic toxicity and
exposure in the derivation of AWQC is warranted--specifically when such
toxicity and exposure are the basis of an RfD, not a chronic effect.
Only in this situation would EPA consider such a basis for its national
304(a) criteria. Using long-term consumption rates to evaluate
potential developmental effects would not accurately reflect meal size
and would be inappropriate for use in such assessments. The separate
distribution of short-term (i.e., consumers-only) consumption estimates
represents the amount of fish an individual consumes in a day, or
multiple days in a short time period, if the person eats fish on that
day. The consumers-only consumption estimate approximates a serving
size for women of childbearing age or for children. The intent is to
characterize consumption over a very short period of time, not as an
average or per capita value over a longer period of time. We recommend
the use of the short-term (consumers-only) consumption values in
assessing developmental risks to children or women of childbearing age.
However, we intend to routinely base our national 304(a) criteria on
the recommended fish intake rate for the general population. One
commenter appears to have incorrectly assumed that EPA would normally
base its national criteria on
[[Page 66469]]
acute toxicity scenarios. EPA acknowledges that it may have overstated
the likelihood that children are more highly exposed in terms of the
frequency of their consumption of freshwater and estuarine fish,
although this may certainly be true for various subpopulation groups.
However, the CSFII data clearly show that children do consume more fish
per unit body weight than do adults. Therefore, as stated above, we
believe it is useful to provide intake defaults to States and
authorized Tribes for children, and we have specifically used childhood
fish consumption rates (to the extent allowable by the CSFII data) as
advocated by the commenter.
EPA disagrees with the comment that the sportfisher default
assumption (i.e., that 17.5 g/day based on the 1994-96 CSFII data
represents average consumption rates for this population group) is not
supported by available studies or by the Exposure Factors Handbook. The
value of 17.5 g/day falls within the range of mean values from
sportfisher/angler studies reviewed by EPA. The Exposure Factors
Handbook indicates that mean intakes from recreational freshwater
studies ranged from 5 to 17 g/day, with mean values from the key West
et al. studies used in the GLI between 12.1 and 16.7 g/day (USEPA,
1997a). Furthermore, the default rate recommended here for the AWQC is
representative of consumption of both freshwater and estuarine fish
species, not freshwater species only. We are also aware that some of
the sportfisher studies that support higher estimates (e.g., 39 g/day)
include marine species.
EPA's fish intake assumption is that all of the consumed fish is
taken from one particular waterbody. This is to ensure that any
population can safely eat fish from waters designated for fishing,
including those who may rely on a single source for their fish (for
additional discussion on this issue, see response to Comment E.2,
Assumption That All Fish Consumed Is Contaminated at the Criteria
Level).
EPA disagrees with the idea that using a 90th percentile value as a
default is inappropriate because of the RSC factor. The RSC is used to
account for other sources of exposure and, thus, is independent of
potential exposures from fresh/estuarine fish. The fresh/estuarine
species are not double-counted, as the commenter suggests. (For
additional discussion on RSC, refer to the responses in the RSC section
below.)
8. Effect of Cooking on the Contaminant Concentration
Comments--Commenters stated that the concept of changes in
contaminant level caused by cooking is important to recognize. They
recommended that a loss from cooking should be accounted for and that
EPA should provide factors in order to calculate this loss into
criteria. However, one commenter did not believe that increases caused
by cooking should be factored into criteria. One commenter stated that
it is not appropriate to assume no loss as a default when no data exist
to account for it. Another recommended that the chemical structure be
assumed as constant before and after cooking. One commenter stated that
the relevance of cooking methods is not clear.
Response--EPA has stated its intention to assume no loss from
cooking unless there are adequate data to characterize such a loss. We
are aware of some studies on cooking loss and provide reference to
quantified information in the 2000 Human Health Methodology. However,
we believe it is important to consider both losses and gains in the
chemical contaminant from cooking. EPA has also received input from
several States regarding the difficulty in making such adjustments on a
routine basis. We continue to evaluate this issue in the context of the
national 304(a) criteria. We believe that providing guidance on making
such adjustments may be useful in the Exposure Assessment TSD volume
for States or Tribes that wish to modify their criteria accordingly.
However, EPA does not intend to provide specific cooking loss default
factors.
9. Inclusion of Marine Species in the Default Rate
Comments--A commenter stated that coastal States have a need to
derive water quality criteria for saline waters under their
jurisdiction and, therefore, requested additional consideration of
marine fish consumption. Another commenter requested that EPA provide
greater clarification on its policy not to include marine species,
again believing that States and Tribes need to include this in their
criteria development.
Response--In the 1998 draft Methodology revisions, EPA recommended
inclusion of fresh/estuarine species only for the intake parameter, and
accounting for the intake of marine species as part of the RSC. We
consider this appropriate because the 304(a) water quality criteria are
applicable to discharges from fresh and estuarine waters, not deep
marine waters. EPA's 304(a) water quality criteria apply to navigable
waters of the United States up the three miles off-shore. However, EPA
also says that coastal States and authorized Tribes could consider
total fish consumption (fresh/estuarine and marine species) when
appropriate for protecting the population of concern. It is important
that the marine intake component not be double-counted with the RSC
estimate. We maintain our default policy decision and the flexibility
afforded to a State or authorized Tribe to base its criteria on
alternative assumptions.
10. Precision of the Drinking Water Parameter
Comments--A commenter interpreted EPA's discussion on significant
figures as indicating that the drinking water intake should not be
factored into that determination because the number represents a
science policy value. The commenter also requested that EPA specify a
level of protection represented by the AWQC.
Response--The commenter has misunderstood EPA's discussion in the
1998 draft Methodology revisions on significant figures; they have
extended the discussion to an evaluation of overall criteria
conservativeness via statistical analysis. We stated that the AWQC
should not necessarily always be limited to one significant figure
because the 2 L/day drinking water value, although supported by data,
represents a science policy decision. The discussion only addresses the
issue of significant figures, not characterization of criteria
protectiveness. For discussion of the issue regarding the population
protected by the criteria level, refer to the response for Comment B.3,
Protectiveness of the Methodology.
11. Redesignation of Salmon as a Marine Species
Comments--Some commenters disagreed with EPA's reclassification of
salmon to the marine category. They stated that EPA has ignored salmon
biology and life history, that salmon is an anadromous species, and
that salmon eggs, fry, and juveniles take up chemicals. Commenters
specifically criticized EPA for ignoring steelhead salmon's life
history. Three commenters thought the redesignation is reasonable. One
had no objection to the redesignation for threshold toxicants but did
object for carcinogenic effects based on a linear low-dose
extrapolation, because it would not account for exposures of salmon to
ubiquitous chemicals (e.g., PCBs) contributing a substantial portion to
total exposure. Another commenter who supported the redesignation
advocated flexibility
[[Page 66470]]
regarding coastal sportfisher consumption.
Response--EPA has not ignored the life history of salmon. We
provided information on the known biology and life history of the
species consumed that were included in the CSFII survey, the basis of
the default values, in our 1998 draft Methodology revisions. The term
anadromous generally refers to a species that spawns in fresh water or
near-fresh water and then migrates into the ocean to grow to maturity.
It can also refer to an ocean species that spawns in fresh/near-fresh
waters. The life cycles of anadromous species vary as to whether they
remain in fresh/near-fresh waters until they die or whether they return
to ocean waters after spawning. As such, the description provided by
EPA in the 1998 draft Methodology revisions is correct and does not
conflict with the term anadromous. The CSFII food codes for salmon do
not indicate the source of the salmon (e.g., land-locked freshwater,
farm-raised, or wild). We based our allocation of salmon between
freshwater and marine habitats on commercial landings data provided by
the National Marine Fisheries Service for the period 1989-1991. All
landings of Pacific salmon, including chum, coho, king, pink, or
sockeye, were assigned to the marine habitat. All land-locked Great
Lakes salmon and farmed salmon received the classification of fresh
water. The resulting apportionment for salmon was 1.18% to the fresh-
water habitat and 98.82% to the marine habitat. We believe this is
appropriate for our national default intake rates.
EPA understands that steelhead salmon, also known as steelhead
trout (Oncorhynchus mykiss), is an oceangoing version of rainbow trout
with a complicated life history, and may spend a significant portion of
its lifetime in fresh waters. States and authorized Tribes have the
flexibility to use different assumptions in deriving their water
quality criteria, as we stated in the 1998 draft Methodology revisions.
That is, States and authorized Tribes could make alternative
assumptions to specifically account for steelhead salmon intake. We
strongly encourage States and authorized Tribes to do so, as reflected
by the recommended fish intake hierarchy of preferences. However, we do
not intend to ignore the contribution from salmon in the calculation of
our 304(a) criteria. We recommended accounting for this as part of the
RSC, thereby ensuring that the criteria would account for the
contribution of a contaminant from marine salmon.
12. Studies on Sportfishers and Subsistence Fishers
Comments--Two commenters stated that in summarizing various
sportfisher and subsistence fisher studies, EPA failed to provide
direction on how States or Tribes can use and interpret the
information. One commenter requested additional guidance on the use of
local data, while cautioning about such data's reliability. Commenters
also listed errors, discrepancies, or missing information from numerous
studies that appear in the 1998 draft TSD. One commenter recommended
separating studies by type, population, and basis for consumption rate
(presumably referring to habitat designations of fish), along with
providing comments on the studies. Another stated that many angler
studies are biased because the respondents are more ``avid'' in their
fishing habits, and a study of fresh-water anglers from Maine might
serve better as the basis of EPA's default for sportfishers.
Response--It is EPA's intention to provide summaries of various
studies for States and Tribes to consider using and, as such, the
Agency is merely providing information, not critiquing or endorsing
particular studies. We do not intend to rank the studies because there
are significant differences in the purposes and limitations of each
study, in addition to the fact that consumption rates vary
significantly throughout the country. Therefore, any particular study
may be most appropriate to the State or Tribe's particular
circumstances. However, we are committed to providing accurate
information and intend to correct errors or missing information that
would make the summaries of greater use to States and Tribes. We have
reviewed the commenters' listed errors or omissions and made
appropriate changes. EPA disagrees that any of the sportfisher studies
are biased from ``avidity'' among recreational anglers. Although the
rates may vary significantly from study to study, the studies
specifically sample fishing patterns of these groups and are the most
appropriate data for prospective use by States and Tribes. We
considered the Maine angler study along with the others presented in
the 1998 draft TSD to evaluate the range of mean values before
recommending the default value. However, we do not believe this
particular study is necessarily best suited for deriving a national
default value. Just as with EPA's national 304(a) criteria, States and
Tribes always have the flexibility to use other local- or regional-
specific studies. We have provided additional guidance on how to
consider the studies included in the Exposure Assessment TSD.
13. USDA Continuing Survey of Food Intake by Individuals (CSFII)
Comments--Some commenters believed that the CSFII data are
appropriate for deriving AWQC and supported their use in the hierarchy
of choices. Others stated that the CSFII data are not appropriate
because they include marine species, and combine recreationally and
commercially acquired species. One commenter suggested that a
significant fraction of the default rate would include farm-raised
fish, which would not bioaccumulate the same as wild fish. One
commenter stated that the default inappropriately assumes consumption
from a single waterbody. Two commenters stated that the CSFII data are
biased toward individuals consuming large quantities of fish (assuming
constant consumption every day and failing to consider those people who
consume less frequently). One of these stated that the CSFII assumes
that participants who did not eat fish during the study period are not
fish eaters. Several commenters recommended that longer term studies be
used, one specifically stating the difficulty in estimating the upper
end of the distribution. Comments also referred to or recommended data
from NPD Research Inc. or the Tuna Research Institute, presumably
referring to the National Purchase Diary (NPD). One commenter assumed
that the CSFII default estimates exclude individuals who consume fish
but did not report consumption during the sampling period. Another
questioned dividing reported consumption by the days of the survey and
incorporating nonconsumption. Instead, this commenter recommended using
the positive values only (``acute consumers'') for determining default
intake rates, which it believed to be consistent with the concept of
identifying the population to be protected. One commenter also
indicated that intake rates do not vary significantly for fish obtained
from different sources--that is, fresh or marine waters. Another stated
that the CSFII data assume short-term consumption is representative of
long-term consumption. One commenter advocated that EPA use
probabilistic methods to derive AWQC.
Response--The comments are incorrect about the exclusion of
respondents who did not report fish consumption during the CSFII
sampling period. The general population,
[[Page 66471]]
recreational fisher, and subsistence fisher default values all include
both CSFII respondents who reported eating fish during the sampling
period and respondents who reported zero consumption (what the
commenter referred to as ``non-consumers''). The CSFII mean values are
not biased. Specifically, the intraindividual variation does not bias
estimates of the mean intake of the population. The estimates of the
upper percentiles of per capita fish consumption based on the short
sampling period data may be biased upward, thereby resulting in a
conservative estimate of risk. However, the extent to which this is
overestimated is not knowable. We note that we did not rely exclusively
on the CSFII data; rather, the data were analyzed with those from other
studies (especially for recreational fisher and subsistence fisher
estimates) to evaluate and corroborate our decision. We believe the
CSFII data are representative of fish intake rates among the general
population. As part of the CSFII analysis, sampling weights were
adjusted to account for nonresponse and were subsequently reweighted
using regression techniques that calibrated the sample to match
characteristics correlated with eating behavior.
EPA generated mean and percentile estimates of daily average per
capita fish consumption based on the USDA 1994-96 CSFII. The strengths
of this survey for supporting estimates of per capita food consumption
are twofold. First, the survey design is structured to obtain a
statistically representative sample of the U.S. population. Second, the
survey is designed to record daily intakes of foods and nutrients and
to support estimation of food consumption. These features are in direct
alignment with the objective of producing current, per capita fish
consumption estimates for the U.S. population. The 1994-96 CSFII
collected two non-consecutive days of food consumption data from a
sample of 11,912 individuals in the 50 states and the District of
Columbia. The method employed to collect dietary intake data also
strengthened the CSFII design for supporting per capita consumption
estimates. For example, the survey was administered by an interviewer
on both days of data collection. For these reasons, we believe that the
1994-96 CSFII is the best source of data on a nationwide basis for
estimating fish consumption by the U.S. population.
The NPD study was conducted over 25 years ago. The NPD is the basis
of the 6.5 g/day default value that EPA has historically used for
fresh/estuarine fish consumption. We have received consistently strong
input from many of our stakeholders (including States and Tribes) who
consider the 6.5 g/day value inadequate and advocate the use of much
more recent data. The Agency also believes that such an update is
needed. We are not aware of any subsequent major survey conducted
during a 30-day period as was done by the NPD. The Agency does not
believe that the year-long study of 29 people mentioned by one
commenter is appropriate to use for a national default value. The use
of probabilistic methods was discussed earlier in our response to
Comment B.3, Protectiveness of the Methodology.
EPA also believes that its discussion of identifying population
groups to protect is not contradicted by its combining positive and
zero values to estimate long-term or average consumption. We reiterate
here that we believe the summation of the amounts of fish consumed by
each individual across the 2-day reporting period for the CSFII 1994-96
data (formerly a 3-day reporting period), followed by dividing that
total individual consumption by 2, is a reasonable approach to
estimating average consumption. The CSFII did not specifically ask
questions on whether respondents consume fish or how often and,
therefore, it is not possible to distinguish fish consumers from fish
nonconsumers. EPA is aware from other major surveys that most people
consume fish--at least episodically--and, therefore, believes that
using the positive and zero values from the CSFII is a reasonable
method of estimating average intake. We contrast this to using only the
subset of survey responses where fish was actually consumed as a method
to estimate an ``acute consumer,'' that is, to provide an estimate of
the amount of fish consumed in the context of acute or short-term
exposures (not in the context of average or long-term exposures).
The commenters are also incorrect about the inclusion of marine
species. The proposed default rates for the general population, as well
as for children and women of childbearing age, are based on freshwater
and estuarine species only. The CSFII study does include marine species
and EPA has additionally provided States and Tribes with these data in
the Exposure Assessment TSD; however, they are not included in the
default estimates of national freshwater and estuarine fish
consumption. According to the CSFII data, most persons in the general
population appear to consume more marine species than fresh/estuarine
species. However, EPA supports State/Tribal use of local or regional
data that indicate otherwise. We have not made any specific assumptions
regarding farm-raised fish and their contribution to the default intake
rate, nor have we received any information that would allow us to
characterize (or discount) the amount that farm-raised fish contributes
to the national default value or to differentiate bioaccumulation
levels.
14. Use of Uncooked or As Consumed Fish Weight for Default Intake Rates
Comments--One commenter stated that either raw weight or cooked
weight can be appropriate as long as the effect of cooking on the
contaminant is accounted for. Some commenters stated that the cooked
weights are the most technically defensible, because they are the basis
for the consumption estimates. However, others believed the default
intakes should be adjusted to reflect uncooked weights, with one
commenter concerned that a cooked weight would result in incomplete
accounting of exposure to threshold toxicants. One commenter also
pointed out the difficulty of making appropriate adjustments to the BAF
because of uncertainties in concentration levels of contaminant due to
cooking and that many cooking techniques result in retention of fish
fluids. Another commenter stressed the need to use uncooked weights in
order to be consistent with fish tissue studies and BAF values. One
commenter expressed concern that use of cooked weights would produce an
inadequately protective criterion for mercury, while another believed
that cooked values introduce a source of uncontrolled variability.
Response--We have considered the pros and cons of using uncooked/as
consumed weights on several levels. First, the intake parameters of the
criteria derivation equation are intended to capture ingestion--that
is, what people actually consume and are exposed to. By and large,
people consume cooked fish, and if raw shellfish or sushi was consumed
by the CSFII respondents, those intakes were included in the as
consumed weights. This assumption is also consistent with the dietary
estimates based on prepared foods (not raw commodities) that are made
by both EPA's pesticide program and the Food and Drug Administration
(FDA) Total Diet Study program. We also considered the ``consistency''
issue in the context of the fact that the CSFII survey respondents
estimated the weight of fish that they consumed. Similar to the CSFII,
EPA's GLI was based on a consumption survey of fish intakes for
prepared meals. EPA additionally considered the effect of the
[[Page 66472]]
cooking process. There are comparatively few chemicals for which
measurements are available, and the process is complicated further by
the different parts of a fish where the chemical may accumulate, the
method of preparation, and how the cooking process may transform the
chemical. What is certain is that the mass of the contaminant will
either remain constant or be reduced. The resulting concentration is
harder to predict. In the 1998 draft Methodology revisions, we
recommended the use of as consumed weights and an adjustment of the
bioaccumulation factor for cooking loss, if information was available.
Otherwise, we recommended using the as consumed weight along with the
full bioaccumulation factor (unadjusted for cooking loss), which would
produce slightly more stringent AWQC. We have also received input from
stakeholders regarding potential confusion over the fact that uncooked
weights are used in the Agency's fish advisory program and that having
two sets of values may prove confusing to States and Tribes, as well as
the general public. Furthermore, the measures of a contaminant in fish
tissue samples that would be applicable to either compliance monitoring
or the permitting program are related to the uncooked fish weights.
Therefore, EPA has reconsidered its position based on these facts
and despite the fact that the as consumed values more accurately
represent actual intake, we will derive our national 304(a) criteria on
the uncooked weight fish intakes. The approach of using an uncooked
weight in the calculation will result in somewhat more stringent AWQC
(studies indicate that, typically, the weight loss in cooking is about
20%). We will also provide guidance on site-specific modifications in
the Exposure Assessment TSD. Specifically, we will describe an
alternative approach for calculating the AWQC using the as consumed
weight (again, more directly associated with exposure and risk) which
is subsequently adjusted by the approximate 20% cooking loss to a
resultant uncooked equivalent. Thus, the AWQC conversion to an uncooked
equivalent can be consistently used between State/Tribal standards
programs and still represent the same relative risk as the as consumed
value. It is important to understand that the two approaches will not
result in the same AWQC value. Whereas the as consumed approach is more
scientifically rigorous and represents a more direct translation of the
as consumed risk to the uncooked equivalent, it may be too intensive a
process to expect of State and Tribal organizations whose resources are
already constrained.
Relative Source Contribution (RSC)
15. Default Percentages and RSC Floor of 20% and Ceiling of 80%
Comments--A commenter criticized EPA's recommended RSC default rate
in the face of uncertainty about other routes of exposure. Another
commenter considered the ceiling of 80% to be a redundant uncertainty
factor. Other comments suggested the use of an 80% RSC for
bioaccumulative chemicals so that the contribution from fish
consumption would not be underestimated, did not support the range of
20% to 80%, or requested additional justification for the assignments
of 20%, 50%, or 80%.
Response--EPA has recommended using the 20% RSC default when routes
of water exposure other than oral or sources of exposure other than
fish and water are anticipated, but adequate data are lacking to
quantify those exposures. When data are adequate, they should be used
instead of the default. If it can be demonstrated that other sources
and routes of exposure are not anticipated for the chemical in question
(based on information about its known/anticipated uses and chemical/
physical properties), then the 80% ceiling is recommended. The ceiling
is intended to provide adequate protection for those who experience
exposures (from any or several sources) higher than available data
indicate. For many of the chemical contaminants that EPA evaluates,
data are not available on multipathway exposures. It is possible that
as we progress with our development of a cumulative risk policy, we may
find an 80% RSC to be underprotective. This concern was expressed
during the scientific peer review workshop on the Methodology. One
commenter misunderstood the application of lower ceilings (i.e., 50%,
20%) when existing information indicates no other media-specific uses
or sources. Also, some chemicals that bioaccumulate in fish also
bioaccumulate in other meat and dairy products (e.g., dioxins).
Therefore, to simply assume an 80% default in all cases would not be
appropriate. The RSC approach allows for an apportionment of 80% when
information indicates that other exposures are not relevant for the
chemical being evaluated. EPA has added discussion in the final
Methodology to address these situations and to better explain the
application of the lower ceilings.
16. Duplication of Fish Intake Assumptions
Comments--Commenters stated that applying an RSC factor results in
a double-counting of fish from other sources.
Response--The commenters are incorrect. The fish intake default
used in the equation accounts for fresh and estuarine species only. The
RSC factor potentially applies to nonfish dietary intake, air
exposures, and marine fish species. To protect humans who additionally
consume marine species of fish, the marine portion should be considered
as part of the ``other sources of exposure,'' that is, part of the RSC
or dietary value. EPA specifically emphasized in the 1998 draft
Methodology revisions that States and authorized Tribes need to ensure,
when evaluating overall exposure to a contaminant, that the marine fish
intake is not double-counted with the dietary intake estimate used.
This applies if the State or authorized Tribe chooses to account for
total fish consumption (i.e., fresh/estuarine and marine species) in
the fish intake parameter used in the AWQC equation.
17. Exposure Route Differences
Comments--EPA received support for its rationale on accounting for
differences in bioavailability and absorption between exposure routes
when data are available, and assuming equal rates when data are absent.
Response--We acknowledge this support.
18. Need for an RSC Factor/Considering Multiple Routes of Exposure
Comments--Commenters supported the greater emphasis on RSC,
including the use of empirical data. Some stated that EPA should give
full consideration to multiple routes of exposure (i.e., ingestion,
inhalation, dermal), with emphasis on the variety of water-related
activities, cultural practices, and lifestyles. Several commenters
pointed to published studies on assessing inhalation and dermal
exposures, and two commenters advocated that EPA determine when there
is a need to factor in these exposures, based on available information
on the chemical. One commenter stated that there are circumstances
where inhalation exposures can be a significant portion of total
exposure (e.g., for some chemicals during showering). However, another
suggested that consideration of inhalation and dermal exposures is
premature. Two commenters stated that uncertainty factors, severity of
effects, essentiality, and additive/synergistic
[[Page 66473]]
effects should be factored into the RfD apportionment, with one
believing that this should also include the option of developing less
stringent criteria when there is great uncertainty in the data. Five
commenters stated that they believe the RSC/Exposure Decision Tree
concepts represent an unnecessary safety factor or should not be
considered. One suggested that the water quality criterion should
relate only to water exposures. Two commenters suggested that factoring
in other exposures is ``penalizing'' the AWQC and makes them overall
environmental exposure criteria. Another questioned the need to
apportion the RfD, but focused on drinking water regulations, stating
that accounting for other sources of exposure would likely have no
benefit, presumably due to conservatism in the RfD derivation (yet
acknowledging that those uncertainty factors are independent of the
exposure assessment). Several commenters recommended that EPA
reconsider the SAB's advice not to routinely apportion the RfD. Others
believed that the RSC should be used only for site-specific criteria,
or that States should have the flexibility to make adjustments for
local conditions. Two commenters also stated that the Exposure Decision
Tree is unclear, is overly complicated, or has unrealistic data
requirements. Another stated that the approach is generally desirable
but that EPA needs to provide a greater and more easy-to-follow
explanation of the rationale, indicating policy judgments where they
occur. However, other commenters supported the Decision Tree approach
for its facilitation of identifying the decisions necessary to select
the most appropriate RSC value and considered it scientifically valid.
One commenter cautioned that if probabilistic analysis techniques are
used, their application must be valid and underlying assumptions
clearly indicated. Commenters expressed the need for data to avoid the
20% default, others stated that defaults should be avoided altogether,
and one recommended a 100% RSC for highly bioaccumulative chemicals.
One of the supporters believed that the approach is a reasonable
compromise between avoiding problematic increases in exposures to
substances and not setting unduly restrictive requirements. A commenter
questioned how new data would be considered in the context of RSCs
based on older data. Another recommended that non-zero values for other
exposure sources not be assumed unless a significant number of samples
are positive. It was also recommended that EPA coordinate the RSC
policy with other Agency programs.
Response--EPA disagrees that the RSC represents an excessive or
unnecessary safety factor. The purpose of the RSC is to ensure that the
level of a chemical allowed by a criterion or multiple criteria, when
combined with other identified sources of exposure common to the
population of concern, will not result in exposures that exceed the RfD
or POD/UF. The policy of considering multiple sources of exposure when
deriving health-based criteria has become common in EPA's program
office risk characterizations and criteria and standard-setting
actions. Since the SAB expressed concerns in 1993, numerous Agency
workgroups have evaluated the appropriateness of factoring in such
exposures and concluded that it is important for adequately protecting
human health. Consequently, Agency policy has evolved significantly
over the last 6 years. Various EPA program initiatives and policy
documents regarding aggregate exposure and cumulative risk have been
developed, and include consideration of inhalation and dermal
exposures. Additionally, accounting for other exposures has been
discussed in recent mandates (e.g., the Food Quality Protection Act)
and, thus, is becoming a requirement for the Agency. The RSC approach
has been shared with other EPA offices, and efforts to coordinate
policies on aggregate exposure, where appropriate, have begun. EPA
intends to continue developing guidance on the RSC issue and guidance
to address the concern that human health may not be adequately
protected if criteria allow for higher levels of exposure that,
combined, may exceed the RfD or POD/UF. We also intend to refine the
2000 Human Health Methodology in the near future to incorporate
guidance on inhalation and dermal exposures. As stated previously, we
are required to derive water quality criteria under Section 304(a) of
the CWA and do not intend to derive site-specific criteria for
individual waterbodies. However, States and authorized Tribes do have
the flexibility to make different exposure and RSC estimates based on
local data.
Uncertainty factors used in the derivation of the RfD to account
for intra-and interspecies variability and the incompleteness of the
toxicity dataset(s)/animal studies are specifically relevant to the
chemical's internal toxicological action, irrespective of the sources
of exposure to humans. The Agency's policy is to consider and account
for other sources of exposure in order to set protective health
criteria. We disagree that uncertainty in the data should result in
less stringent criteria. However, we have provided additional
clarification on the guidance allowing less stringent assumptions when
multiple sources of exposure are not anticipated.
The adequacy requirements for the Exposure Decision Tree are not
unduly restrictive. The ideas of representativeness, quality assurance,
and sampling size are fundamental to properly conducted monitoring
studies. Furthermore, the minimal requirement of samples to make an (at
least, nominally) acceptable estimate of average and high-end exposure
from that relative source (i.e., 45 samples) is not unreasonable
guidance. EPA also believes that the number of decision points in the
Decision Tree for any particular chemical are not excessive. We have
provided additional discussion in the 2000 Human Health Methodology in
order to clarify numerous issues on the Decision Tree approach,
including the discussion on the use of defaults. We believe that
probabilistic techniques are potentially appropriate for use and agree
that they must be valid, appropriately applied, and clearly presented.
Regarding changes in ambient chemical concentrations that would
affect the RSC calculation, States and authorized Tribes have the
opportunity to make changes in their water quality standards during
triennial reviews, and EPA would evaluate those changes based on
information submitted with the proposed changes. Similarly, EPA would
consider changes to AWQC when significant changes in sources of
exposure occur that affect the default values.
19. Use of RSC With Carcinogenic Effects Based on Linear Low-Dose
Extrapolation
Comments--A commenter advocated the use of an RSC factor with
carcinogenic effects based on linear low-dose extrapolation in order to
account for other sources of exposure.
Response--EPA does not apply the RSC to carcinogenic effects based
on linear low-dose extrapolation because the AWQC are being determined
with respect to the incremental lifetime cancer risk posed by a
substance's presence in the exposure sources relevant to the specific
criterion, not in terms of an individual's total cancer risk from all
sources of exposure. In the case of carcinogens based on nonlinear low-
dose response extrapolation or a noncancer endpoint where a threshold
is assumed to exist, non-water
[[Page 66474]]
exposures (i.e., non-drinking water and non-fish ingestion exposures,
and inhalation or dermal exposures) are considered when deriving the
AWQC. The rationale for this approach has been that for pollutants with
effect thresholds, the objective of the AWQC is to ensure that an
individual's total exposure does not exceed that threshold level.
Health-based and medium-specific criteria values for carcinogens based
on a linear low-dose extrapolation typically vary from other medium-
specific criteria values in terms of the concentration value, and often
the associated risk level. Therefore, the RSC concept could not apply
unless all risk assessments for a particular carcinogen based on a
linear low-dose extrapolation used the same concentration value and
same risk level; that is, an apportionment would need to be based on a
single risk concentration value and level.
20. Use of Subtraction or Percentage Methods in RSC Apportionment
Comments--One commenter advocated the subtraction method instead of
the percentage method for RfD apportionment, and advocated the use of
central tendency values. This commenter criticized the percentage
method as irrational and likely to produce overly stringent criteria.
In addition, it was stated that the percentage method would allow
criteria that could result in exposure levels that exceed the RfD when
combined exposures are high. Other commenters expressed concern over
basing the RSC on current levels of contamination. However, one
believed that the percentage apportionment was reasonable given the
difficulty in alternative apportionment methods (for example, an
apportionment that would minimize the costs of reducing total exposure
to/below a certain amount). One commenter suggested using a multiple
default system.
Response--The first commenter has significantly misunderstood EPA's
policy goals. The argument against use of the percentage approach is
based on the idea that the maximum possible amount of chemical
concentration, after subtracting other sources, should be allocated to
drinking water criteria or standards. This is not EPA's goal nor is it
stated in any relevant mandate. The rationale of deliberately removing
the entire cushion between precriteria levels (i.e., actual levels) and
the RfD, and thereby setting criteria at the highest levels short of
exceeding the RfD, is counter to the goals of the CWA for maintaining
and restoring the nation's waters. It is also directly counter to
Agency policies, explicitly stated in numerous programs, regarding
pollution prevention. EPA has advocated that it is good health policy
to set criteria such that exposures are kept low when current levels
are already low. The subtraction method generally results in
prospective criteria values for a contaminant in a particular medium at
significantly higher levels than the percentage method and, in this
respect, is contradictory to these Agency goals. In fact, many
chemicals have existing levels in environmental media, based on
available monitoring data, substantially lower (compared with the RfD)
than the resulting criteria allow. This is the case with most of the
theoretical examples that one commenter provided to refute the method.
The Agency has modified its policy with the Exposure Decision Tree
approach to allow use of the subtraction method when multiple media
criteria are not relevant. The Agency RSC Workgroup recommended that,
although combined exposures above the RfD may or may not present an
actual health risk, a combination of health standards exceeding the RfD
may not be sufficiently protective. Therefore: (1) Maintaining total
exposure below the RfD is a reasonable health goal; (2) there are
circumstances where health-based criteria for a chemical should not
exceed the RfD (either alone or in combination); and (3) the best way
to prevent exceedance of the RfD is to apportion it when multiple
health criteria are relevant to a given chemical. We believe that the
percentage method is rational in the context of the above goals when
multiple media criteria are at issue. However, as a commenter
suggested, the percentage method does not simply depend only on the
amount of the contaminant in the prospective criterion source. It is
not a set amount. It is intended to reflect health considerations, the
relative contribution of other sources, and the likelihood for ever-
changing levels in each of those multiple sources (due to ever-changing
sources of emissions and discharges). The percentage method does not
break any ``logical link,'' as a commenter suggested (the commenter
referenced an unpublished report from discussions prior to the
development of the Exposure Decision Tree approach). EPA is interested
in knowing the amounts of current exposures, including water, and is
always cognizant of their relationship to the RfD (one commenter
suggested that EPA does not compare actual exposures to the RfD; this
comparison is always known). We have historically evaluated chemicals
in the context of their current levels (i.e., ambient levels prior to
either criteria development or regulatory activity). Evaluating these
levels, along with the hazard identification, has historically formed
the basis for prioritization and whether the Agency would pursue
criteria or standards development. We disagree with the comment that
criteria should be set without regard to the actual level of the
contaminant. Actual levels are advocated by a commenter for use with
the subtraction method. In the case of multiple criteria for a given
chemical, the commenter's claim that the subtraction method will ensure
that ``an individual's exposure to a chemical does not exceed the RfD''
is not necessarily guaranteed if criteria for other media allow for
concentrations in environmental media that, combined, may result in
exposures greater than the RfD. EPA acknowledges that the percentage
approach outcome varies depending on the magnitude of current
exposures, and we have sought to provide greater clarification on this
policy issue in the 2000 Human Health Methodology. Of course, depending
on the levels from each source, the subtraction method can also produce
unstable values--that is, they could vary from very high, to moderate,
to very low, even to a negative number.
As previously indicated, probabilistic analyses are appropriate
when they are validated techniques that are applied correctly and
supported by adequate data. However, much of the time, the amount of
data available to describe distributions of exposure from various known
sources to the U.S. population--for use in setting nationwide
criteria--is inadequate to support meaningful probabilistic analyses.
Nevertheless, rather than simply using a default value in every
instance, the Agency attempts to compare exposure intakes based on
available data to estimate their relative contribution to the total--
given that understanding the degree to which their concentrations vary,
or making any distributional analysis, is not possible. When multiple
criteria are at issue, the criteria values are based on the best
available information, with an assumption that there may be enough
relative variability such that an apportionment (relating that
percentage to the RfD) is a reasonable way of accounting for the
uncertainty regarding that variability. Again, in the context of making
an estimate of potential national exposures, there is great uncertainty
in the range of exposures, and as previously stated, the goal is not to
allow a water criterion to use up the
[[Page 66475]]
``space'' between the total exposure and the RfD. An example of the
percentage apportionment's potential use is when pesticides are at
issue. It does not make sense to allow the water criterion to use up
that space when (in terms of the chemical's intended uses) the dietary
route is obviously the ``direct'' source of exposure. When the course
of pesticide tolerance-setting activities may, over time, vary the
exact amount of the RfD taken up, an apportionment may also be best for
pesticide program planning. The Exposure Decision Tree has allowed for
the use of the subtraction approach when only one criterion is
relevant. Also, given the future need to develop cumulative risk
policies, the subtraction method in these cases could be a short-lived
option.
Finally, one commenter incorrectly assumed that the percentage
method would allow criteria that could result in exposure levels that
exceed the RfD when combined exposures are high. Again, this commenter
incorrectly assumed that EPA is not aware of the relationship of the
estimated exposures to the RfD. The Exposure Decision Tree approach
states that, in these situations, a risk management decision would be
made in order to reduce exposures to levels that would prevent
exceedance of the RfD. We have provided greater clarification on this
issue in the 2000 Human Health Methodology. We have also provided
clarification on the use of central tendency values when estimating
exposures, which we do not believe to be fully adequate for protection
of human health when setting national 304(a) criteria.
F. Bioaccumulation
1. Use of Bioaccumulation Factors (BAFs) in General
Comments--Overall, commenters were not adverse to incorporating
bioaccumulation into criteria derivation, but were concerned with the
methodology EPA proposed to use. Most comments received were focused on
the general use of BAFs. Because of the site-specific nature that BAFs
can take, several commenters are concerned with applying national BAFs
developed from a limited set of data and array of aquatic systems, or
from a model, to all waterbodies in the United States. Some commenters
did not agree with EPA's proposed BAF tiered hierarchy. These
commenters stated that EPA should not derive single national BAFs
because there is substantial variation among waterbodies in factors
that influence bioaccumulation (e.g., food chain, metabolism,
bioavailability, loading history). They recommended that BAFs be
calculated on a site-specific basis, or that field-derived BAFs be used
in conjunction with modeled BAFs in a weight-of-evidence approach to
select a final BAF. Some commenters also wanted the BAF guidance to
more clearly state how it applies to different groups of compounds
(e.g., nonionic organics, ionic organics, metals, organometallics).
Several commenters did agree with EPA that field-derived BAFs better
reflect potential exposure to chemicals from all sources than BCFs and
incorporate factors in the field (e.g., food chain, metabolism,
chemical loading history, temperature) that can affect bioaccumulation.
Response--Although EPA acknowledges there are site-specific factors
that affect bioaccumulation, we disagree that national BAFs should not
be derived. For some pollutants (e.g., PCBs, methylmercury),
biomagnification through the food chain can be substantial. Using a
BCF, which only accounts for exposure from the ambient water, could
substantially underestimate the potential exposure to humans for some
chemicals and result in criteria that are underprotective of the
designated uses. Since publishing the 1980 Methodology, there has been
a growing body of scientific knowledge that clearly supports the
observation that bioaccumulation and biomagnification occur and are
important exposure issues to consider for many highly hydrophobic
organic compounds and certain organometallics (Russell et al., 1999;
Fisk et al., 1998; USEPA, 1998d; Watras and Bloom, 1992; Oliver and
Niimi, 1988; Swackhammer and Hites, 1988; Niimi, 1985; Oliver and
Niimi, 1983). For highly persistent and bioaccumulative chemicals that
are not easily metabolized, BCFs do not reflect what the science
indicates. For this group of chemicals, bioaccumulation (i.e.,
accumulation of a chemical in aquatic biota from all routes of
exposure) should be accounted for in the derivation of water quality
criteria in order to protect against unacceptable risks from
contaminated biota. The use of properly derived BAFs will enable
chemical exposure from all sources to be accounted for in water quality
criteria. The lack of national BAFs would greatly hinder the
development of water quality criteria because many States and
authorized Tribes may not have the resources to develop site-specific
BAFs. We continue to believe that using national BAFs is the most
scientifically valid approach to deriving national AWQC.
EPA acknowledges that data available to derive national BAFs and to
validate the overall bioaccumulation methodology are primarily limited
to persistent, hydrophobic chemicals from selected locations (e.g.,
Lake Ontario, Green Bay, Bayou d'Inde, Hudson River). However, we
believe these chemicals and sites encompass a reasonable range of
chemicals, locations, and ecosystems from which to evaluate the
appropriateness of the bioaccumulation methodology. To obtain better
representation of lotic (e.g., river) systems, we also performed
evaluation of the predictive BAF methods with PCB, pesticide, and
chlorinated benzene data from the Hudson River and Fox River/Green Bay.
In the vast majority of comparisons between the predicted BAFs and
field-measured BAFs using all four methods, the predicted BAFs were in
very good agreement with the field-measured BAFs. We further
acknowledge commenters' concerns that certain portions of the
methodology may not be applicable to some types of chemicals. As a
result, we have developed additional guidance that restricts some
aspects of the methodology to certain types of chemicals. For example,
we have revised the 1998 draft Methodology revisions to remove the use
of Kow x FCM to estimate BAFs for chemicals that have been
consistently shown to be metabolized substantially in aquatic biota
(e.g., certain PAHs) and have clearly differentiated which methods
apply to ionizable chemicals and which do not.
We also recognize that there were some uncertainties in the 1998
draft Methodology revisions on how the BAF methodology would be applied
both nationally and on a site-specific basis. In response to this, we
made substantial revisions to the 1998 draft bioaccumulation
methodology which we believe makes the revised methodology applicable
on a national basis. First, we improved the readability and guidance
presented in the bioaccumulation methodology based on public and peer
reviewers' comments. Specifically, we separated guidance for developing
national BAFs from guidance for developing site- or region-specific
BAFs and revised the Methodology document to make it more clear to the
reader on how EPA will derive national BAFs. Second, EPA expanded the
guidance for deriving site-or region-specific BAFs to better enable
such adjustments to be made by States and authorized Tribes. For
example, we updated, expanded, and made more accessible the databases
used to develop national values for lipid content in aquatic biota and
organic carbon content
[[Page 66476]]
in water. Third, we plan to develop detailed guidance to assist States
and authorized Tribes in designing and conducting field studies to
measure site-specific BAFs and BSAFs (biota-sediment accumulation
factors). This guidance will specify our recommendations for how, when,
where, and how often one should sample water, biota, and sediment for
producing reliable measurements of BAFs and BSAFs.
In addition to improved clarity and expanded guidance, EPA believes
the changes we made to the national BAF methodology address concern
indicated by some public commenters about uncertainty in various
aspects of the methodology. We believe the changes we have made reduce
the uncertainty in several components of the national BAF methodology.
For example, development of separate procedures for deriving BAFs for
different chemical classes (e.g., high vs. low hydrophobicity, high vs.
low metabolism in biota, ionic vs. nonionic organics) will reduce
uncertainty in national BAFs and simplify procedures. As part of these
revisions, we recommended that Kow-based estimates of BAFs
and food chain multipliers (FCMs) not be used for nonionic organics
that are known to be metabolized substantially in targeted biota (e.g.,
some PAHs). Restrictions have also been placed on the use of the BSAF
methodology so that the method is used for the chemicals for which it
is most appropriate.
We clearly recognize that even with these revisions incorporated
into the national BAF methodology, significant uncertainty might exist
in the assessment and application of national BAFs at some sites
throughout the United States because of the influence of site-specific
factors. Therefore, we have more clearly indicated that development of
site-specific BAFs is encouraged and supported when it can be shown
that a national BAF is inappropriate, or when a State or authorized
Tribe prefers to derive a site-specific BAF.
EPA agrees with commenters that in some cases it may be appropriate
to derive a BAF using several of the recommended methods (Methods 1-4),
with the final BAF chosen using a weight-of-evidence approach. We have
provided general guidance on the assessment of uncertainty in using
field-measured BAFs (and BAFs derived using the other methods) when
deriving national BAFs. However, we do not believe that the mere
existence of uncertainty means that national BAFs (and resulting
national 304(a) water quality criteria) cannot be implemented
effectively throughout the United States. For more than two decades, we
have developed and implemented our national 304(a) water quality
criteria (aquatic life and human health) through State, Tribal, and on
occasion, Federal water quality standards programs. Implementation of
this program has relied on the use of national 304(a) criteria as a
cornerstone but has evolved to allow the use of procedures to modify
national criteria by States and authorized Tribes where appropriate.
EPA's national bioaccumulation methodology is consistent with this
programmatic practice, by enabling States and authorized Tribes to
readily adopt national 304(a) water quality criteria into standards
(based on National BAFs) that achieve the CWA goals of protecting
public health while also allowing site- or State-specific adjustments
in situations where national AWQC may be considered overprotective or
in some cases, underprotective.
Comments--Some commenters questioned the application of the BAF
prediction approaches (Tiers 2-4; referred to as Methods 2-4 in the
revised Methodology) on a national scale because the data used to
validate the approaches and develop predicted BAFs come primarily from
chemical partitioning relationships observed from a limited set of
studies (e.g., Great Lakes region).
Response--EPA agrees that the locations for which the BAF
methodology has been fully applied are limited in number (e.g., Lake
Ontario, Green Bay). To address this concern, we have conducted
additional assessments and comparisons among the bioaccumulation
approaches (Methods 1-4) to further validate their usefulness and have
validated the methods using other locations (e.g. Bayou d'Inde, LA, Fox
River/Green Bay, Hudson River, NY). We acknowledge that a model
prediction is not a perfect simulation of what occurs in a natural
aquatic ecosystem and that uncertainty exists in the BAFs. However,
this does not invalidate the usefulness of models validated using data
from the Great Lakes and Hudson River in predicting bioaccumulation in
other ecosystems. Results of analyses that support using a predictive
bioaccumulation approach for a variety of chemicals and aquatic
ecosystems can be found in Burkhard et al. (1997), Burkhard (1998),
Oliver and Niimi (1988), Swackhammer and Hites (1988), and Oliver and
Niimi (1983). Data from these studies clearly indicate that the food
web is a dominate exposure route for many highly hydrophobic chemicals
and that use of BCFs only underestimates exposure. EPA's proposed BAF
methodology does account for some site-specific differences in
bioaccumulation (an issue expressed by commenters) by considering
factors such as percent lipid in the fish consumed and the freely
dissolved concentration of the chemical in the ambient water (i.e., a
baseline BAF). This allows a BAF developed from one set of data and
location(s) to be ``normalized'' and applied to another location. We
believe the approach in the 2000 Human Health Methodology appropriately
balances protectiveness with the uncertainties surrounding the science
currently available to predict bioaccumulation. Comparisons of field-
measured and predicted BAFs demonstrate agreement within an order of
magnitude in the vast majority of cases, and often within a factor of
two to five. Burkhard (1998) observed good agreement between measured
and predicted BAFs for the Lake Ontario food web using the Gobas and
Thomann food web models. For individual commonly detected PCBs and
chlorinated pesticides, the BAFs estimated using the two Gobas and
Thomann models were on average within a factor of 1.2 and 2.5 of the
observed (i.e. field-measured) BAFs, respectively (Burkhard 1998). The
overall uncertainties in each of these two bioaccumulation models
(expressed as the ratio of the 90th to 10th percentile predicted BAF
for each model) were a factor 3.6 and 4.0 for the Gobas and Thomann
models, respectively (Burkhard 1998). Furthermore, Burkhard et al.
(1997) reported that predicted BAFs (using EPA's national BAF
methodology) were within a factor of 5 for 94% (n=32, using laboratory
measured BCFs and FCMs) and 90% (n=48, using predicted Kows
and FCMs) in Bayou d'Inde (Lake Charles, LA). These data comparisons
show the good predictability of the methods used in the national BAF
methodology. Should States or authorized Tribes have information to
suggest that a national BAF is inappropriate for their situation, the
2000 Human Health Methodology specifically allows and encourages
development of site-specific BAFs. With this in mind, we will be
developing guidance on how to collect and interpret field data for the
purpose of deriving site-specific field BAFs. This guidance will
specifically address major sources of variability, including spacial
and temporal factors and species life history.
Finally, to further address concerns that the predictive approaches
used to derive BAFs may not be applicable at a
[[Page 66477]]
national scale, we revised the 1998 draft Methodology to clarify and
limit for which chemicals and under what conditions BAFs based on
Methods 2 to 4 are most applicable. For example, chemicals were grouped
into broad categories based on their persistence and bioaccumulation
potential (e.g., high vs. low hydrophobicity, high vs. low biota
metabolism, ionic vs. nonionic), and we have limited the use of
predicted BAF approaches to selected groups of chemicals for which the
data reasonably support their use (i.e., highly hydrophobic chemicals
that are not expected to be metabolized appreciably). The national BAF
methodology was also changed to indicate that for those chemicals with
sufficient data to indicate they are metabolized, model-predicted BAFs
are not recommended; rather, field BAFs or laboratory BCFs are
recommended. The use of the BSAF methodology has been restricted to
chemicals that are highly hydrophobic (e.g., log
Kow4).
EPA believes these revisions to the 1998 draft Methodology have
improved the Methodology and have addressed many of the commenters'
concerns and questions about uncertainty in applying the various
approaches and BAFs on a national scale.
Comments--One commenter suggested that it is ``scientifically
indefensible to use the field-measured BAF procedure to derive BAFs for
benthic systems.'' They commented that in a benthic-based aquatic food
web, the water column concentration of a chemical is not directly
related to aquatic organism exposure potential for that chemical.
Therefore, their view is that a field-measured BAF may over- or
underestimate bioaccumulation in benthic-based systems.
Response--EPA acknowledges that the concentration of a chemical in
the water column is not directly related to what pelagic organisms
(i.e., fish) are exposed to in a benthic-based system. However, the
concentrations of a chemical in water, sediment, and fish are
interconnected, although they may not be equally partitioned into each
compartment, and residues in fish can be predicted equally well using
either a sediment or water concentration as the starting basis. In the
revised TSD on Bioaccumulation, the relationships between BAFs and
BSAFs have been shown more clearly in order to demonstrate this
interconnectedness. In the BAF methodology, we are assessing exposure
through all routes (i.e., from water, sediment, and contaminated food)
in the aquatic ecosystem. By including all routes of exposure, the BAFs
do not assume simple water-fish partitioning; rather they are an
overall expression of the total bioaccumulation using the concentration
of the chemical in water column as a reference point. Thus, a field-
measured BAF or BASF at any given time is reflective of historic
chemical loadings and bioaccumulation that has occurred. EPA does agree
that a BAF may change over time because of differential chemical
loadings; however, some frame of reference has to be chosen as the
starting point to assess bioaccumulation. EPA has chosen to use the
water concentration as that reference point. Science has shown that
bioaccumulation occurs and is an important exposure pathway to humans
for many chemicals, and EPA cannot ignore bioaccumulation in
development of its AWQC simply because variability and uncertainty
exist. In situations where chemical loadings are highly variable or are
reduced substantially, EPA believes that a field-measured BAF will
still be predictive of what will bioaccumulate in fish until the
concentrations in sediments and benthic organisms are reduced enough to
lead to reduced bioaccumulation. In situations such as this, a revised
site-specific field BAF can be developed to reflect the change in
chemical loading and partitioning.
This issue of field-measured BAFs and benthic-based food webs was
also brought up in public comments made at the stakeholders meeting
held in May 1999. At that time, we asked commenters if they could
recommend another approach to assess bioaccumulation in benthic-based
systems. No other approaches were suggested. We have concluded that in
the absence of any other approaches, field-derived BAFs are good
predictors of bioaccumulation because they integrate biological,
chemical, and physical factors that influence bioaccumulation.
2. Guidance for Deriving Field Bioaccumulation Factors (BAFs)
Comments--Several commenters agreed with EPA that field-derived
BAFs should take precedence over modeled BAFs. However, many commenters
discussed the need for guidance on how to collect and review field data
so that high-quality, field-based BAFs can be derived. Commenters noted
that there are numerous site-specific biological, chemical, and
physical factors that affect bioaccumulation, which should be
considered during design of field sampling programs.
Response--We agree that properly derived field BAFs should take
precedence over modeled BAFs; we have clearly indicated in the 2000
Human Health Methodology that this is our preferred approach for
deriving a BAF. We also acknowledge that, as with any field
measurement, there can be errors in determining field-measured BAFs. In
the development of national BAFs, EPA will attempt to minimize
potential errors or uncertainties by carefully screening the data based
on the criteria outlined in the Bioaccumulation TSD. Furthermore, an
additional validation of national BAFs will be conducted as part of the
external peer review process that occurs for all published 304(a) water
quality criteria. We continue to assert that for many chemicals, a
field-measured BAF is a better gauge of what is occurring in nature
than a laboratory-measured or predicted BCF; the BAF measures the
actual effects of bioavailability, concentration in the water or
sediment, growth dilution, metabolism, and biomagnification rather than
predicting them through use of a model. We do agree with commenters
concerned about the difficulty of collecting and interpreting field-
measured BAFs; however, we believe that States and Tribes can
adequately design and interpret field studies. To assist them in this
task, we will be developing guidance concerning field data collection
and interpretation for site-specific field-measured BAFs and BSAFs.
3. Use of Biota-Sediment Accumulation Factors (BSAFs)
Comments--Several commenters stated that the use of the BSAF
approach for deriving a BAF is inappropriate. Some comments centered
around the perceived lack of validation and peer review of the BSAF
approach, and others focused on the relationship between the water
column concentration of a chemical and its sediment concentration,
represented by the factor socw. One commenter noted
that the BSAF method is simply a means to predict a water concentration
of a chemical of interest from the sediment concentration of that
chemical, the water and sediment concentration of a reference
chemical(s), and the ratio of Kow for the chemical of
interest and the reference chemical(s). A commenter indicated that
loading history of a given chemical directly affects what the value of
socw would be at any given time, and that
socw/Kow (disequilibrium ratio) for the
chemical in question and the reference chemical has to be constant
under the assumptions of the BSAF approach. The commenter stated,
however, that socw/Kow will not be
constant because of
[[Page 66478]]
differential loading histories, and that because the concentration of
the chemical of interest cannot be measured in water, the assumptions
about socw/Kow cannot be verified. In
their view this made the use of BSAFs invalid.
Response--The method of predicting BAFs from BSAFs has been
evaluated for certain pesticides, PCBs, chlorinated benzenes, and
dioxins using two data sets from Lake Ontario (Oliver and
Niimi,1988;USEPA, 1990) and one from Green Bay (USEPA, 1992b). EPA has
also recently completed further evaluation of this method for certain
PCB congeners, pesticides, and chlorinated benzenes in Lakes Ontario,
Green Bay, and the Hudson River. This additional evaluation and
validation work is included in the Bioaccumulation TSD. The evaluations
show that in the vast majority of situations, the BSAFs predict field-
measured BAFs very well.
EPA agrees with the commenter who noted that the BSAF method is
structured to predict water concentrations for chemicals that cannot be
measured for the purpose of directly measuring a field BAF. However,
the BSAF method is more important for its ability to capture the net
effect of biomagnification, food web structure, hydrophobicity,
bioavailability factors, and metabolism on a specific chemical's net
potential for bioaccumulation. The BSAF method is needed to predict
BAFs for chemicals with nondetectable and difficult-to-predict
concentrations in water (e.g., dioxins). No alternative methods to
predict BAFs for such chemicals were identified by either public
commenters or peer reviewers. The BSAF method equation has been
modified (see below) in the Bioaccumulation TSD to clarify the
essential data components of the method. The revised BSAF equation
shows that measured concentrations in water and surface sediment, not a
complete BSAF, are needed for the reference chemical. The equation also
shows that a measured BSAF for the chemical of interest is the most
important component for determination of a BAF when the concentration
in water cannot be measured.
EPA agrees with commenters that the BSAF method should not be used
for all organic chemicals that may be addressed through the 2000 Human
Health Methodology, and accordingly have restricted application of the
method to nonionic organic chemicals with log Kows
4.0. We have also provided more specific guidance on
selection of reference chemicals and use of multiple reference
chemicals to secure the most accurate estimate of a chemical's BAF.
One commenter contended that the BSAF approach for deriving BAFs is
seriously flawed. The concern is that the approach is valid only if a
reference chemical (chemical r) can be found with a sediment-water
fugacity ratio (which represents the differential partitioning of a
chemical between water and sediment) equal to that of the chemical for
which the BAF is being determined (chemical of interest). The commenter
contends that the BSAF approach could validly be used only if it could
be shown that the fugacity ratio is a constant for the chemical of
interest and the reference chemical. The commenter submitted figures to
demonstrate conceptually that two chemicals with radically different
loading histories will have dissimilar fugacity ratios. EPA disagrees
that in order for the BSAF to work, the fugacity ratio has to be
constant, but does agree that in order to best use the BSAF approach, a
general knowledge of chemical loading histories to an ecosystem is
needed to help provide a basis for choosing appropriate reference
chemicals. Such information may be obtained from chemical production
records, historical fish residue monitoring data, or dated sediment
core analysis. We recognize that due to various factors (loading
histories, microbial degradation, etc.) fugacity ratios for both
chemical (i) and (r) may shift over time, leading to the potential for
temporal variability of sediment-water distributions of nonpolar
organic chemicals. Although it was not shown explicitly in the 1998
draft TSD, an important benefit of the BSAF approach is that it can
account precisely for such differences in sediment-water distributions
of nonpolar organic chemicals. The BSAF method is robust to the extent
that the choice of reference chemicals is based on meeting the
sediment-to-water fugacity ratio condition: That the ratios be
similar--they do not have to be constant. The extent that these ratios
for chemicals with log Kows 4 may change with
chemical loading over long periods of time after sediments become
contaminated, and thereby contribute to small shifts in BSAFs and
larger shifts in BAFs, is an issue of possible concern that EPA
recognized in the 1998 draft TSD. EPA noted on page 188 of the TSD
(USEPA, 1998d) that ``BSAFs measured for systems with new chemical
loadings or rapid increases in loadings may be unreliable due to
underestimation of steady-state Csocs.''
To better address the water-to-sediment relationship issue, EPA has
revised the equations that serve as the basis for deriving a BSAF. In
the revised equations, a factor Di/rhas been added, which is
defined as the ratio of the fugacity gradient (modeled as
socw/Kow) between sediment and water for
chemical (i) in comparison to that of a reference chemical (r). The
revised equations are as follows:
[GRAPHIC] [TIFF OMITTED] TN03NO00.022
By definition, socw can be used to relate
chemical i's BSAF to its BAF.fd:
[[Page 66479]]
[GRAPHIC] [TIFF OMITTED] TN03NO00.023
By substituting rearranged Equation 1 into rearranged Equation 2:
[GRAPHIC] [TIFF OMITTED] TN03NO00.024
where:
(BAF.fd)i = BAF expressed on a freely dissolved
and lipid-normalized basis for chemical of interest ``i''.
(BSAF)i = Biota-sediment accumulation factor for chemical of
interest ``i''.
(Csoc)i = Concentration of chemical of interest
``i'' in sediment normalized to sediment organic carbon.
(Csoc)r = Concentration of a reference chemical
in sediment normalized to sediment organic carbon.
(Cwfd)i = Concentration of chemical of
interest ``i'' freely dissolved in water.
(Cwfd)r = Concentration of the
reference chemical freely dissolved in water.
Di/r = ratio between socw/Kow
for chemicals ``i'' and ``r'' (normally chosen so Di/r = 1).
(Kow)i = octanol-water partition coefficient for
chemical of interest ``i''.
(Kow)r = octanol-water partition coefficient for
the reference chemical ``r''.
(socw)i = sediment organic carbon to
water freely dissolved concentration ratio of chemical of interest
``i''.
(socw)r = sediment organic carbon to
water freely dissolved concentration ratio of reference chemical ``r''.
Equation 3 is intended to provide an improved representation of how
the BSAF method/model works. By using Di/r, the new equation
accounts for differences in sediment to water column concentrations
that might exist between the chemical of interest and the reference
chemical because of factors such as loading histories or degradation.
Unlike one commenter's analysis, in which an equation was derived
without the BAF or BSAF, equation 3 shows these quantities as central
to the model; that is, the BSAF is measured and then transformed into a
BAF by estimating the chemical's socw/
Kow. This model could alternatively be described as a
determination of (Cwfd)i from a
measured value of (Csoc)i combined with a
measured value of (C.)i to give an accurate measure of
(BAF.fd)i. However, we believe that equation 3
best describes the BSAF method as allowing measured BSAFs to be
transformed into BAF.fds for the specific purpose of
developing either national or a site-specific water quality criteria
when directly measured BAF.fds cannot be obtained.
When good-quality data are available for reference chemicals (r)
that should have equal or similar sediment-water fugacity ratios as a
chemical (i) whose (BAF.fd)S cannot be measured
directly, then Di/r = 1. When Di/r 1,
it may be estimated based on properties of the chemicals and knowledge
of their loading histories to the ecosystem. Equation 3 provides a
greater degree of flexibility for use of the BSAF method than the
original equation. This flexibility highlights a logical stepwise
transition from measured to fully modeled site-specific BAFs that can
incorporate estimates of Di/r through fate modeling, should
interested parties choose to do so. In such a situation, if the
uncertainty associated with choice of Di/r is perceived to
be too great, a determination of a site-specific
(BAF.fd)i, which still takes advantage of
measured values of (C.)i and (Csoc)i,
could be accomplished if a mass balance model, specifically calibrated
with (C.)i and (Csoc)i, is used to
predict (Cwfd)i. Such an approach
would be time consuming and expensive but would allow prediction of
(BAF.fd)i over time as a function of changes in
(socw)i associated with anticipated
changes in mass loading of the chemical into an ecosystem. In cases
where the intended use of the site-specific criterion is to determine
permit conditions or establish a TMDL, a mass balance model presumably
would have to be developed, and thus use of the model for providing a
(BAF.fd)i would not require an extraordinary
effort. However, as with the BSAF method, it should be noted that mass
balance model predictions of Cwfdi
also cannot be directly validated through measurements. EPA's
appreciation for the value of hybrid models comes from recognition that
incorporation of measured bioaccumulation potentials, including those
provided by the BSAF method, are especially advantageous for those
chemicals with transformation rates, such as metabolism throughout the
food chain, that are presently not accurately known or incorporated
into mechanistic bioaccumulation models.
Finally, we disagree with the circular argument that the BSAF
approach has ``extremely limited utility'' because ``it will not be
possible to demonstrate that socw/Kow is
a constant'' because socw/Kow cannot be
measured directly for one chemical. The inherent limitation for
validation of a predicted BAF because of the inability to measure the
concentration of freely dissolved chemical in water
(Cwfd) applies to any approach/model available
and is not a just criterion for rejection of a BAF method. Validation
may be based on the ability of the BAF to predict concentrations in
fish from predicted values of Cwfd. Data from the
Great Lakes clearly show that such predictions are possible, and
accurate (USEPA, 1998d). It should also be noted that during the
external peer review of the BSAF approach, the peer reviewers stated
``for the chemicals examined (persistent and bioaccumulative),
extrapolation to other circumstances may be reasonable,'' thereby
disagreeing with public commenters. EPA believes that restricting the
use of the BSAF method to highly hydrophobic chemicals, clarifying the
use of reference chemicals, elaborating on the primacy of the sediment-
water fugacity equivalence
[[Page 66480]]
condition for use of the method, and validation with additional data
sets alleviates concerns about using this new method.
4. Dissolved Organic Carbon (DOC) and Particulate Organic Carbon (POC)
Comments--Two comments were received on the DOC/POC approach used
to determine the bioavailable fraction of organic chemicals in surface
water and sediments. Rather than solely use default organic carbon
values, commenters wanted to the ability to select DOC/POC values they
believe are more representative of their waterbody type or site-
specific conditions.
Response--In the 2000 Human Health Methodology, EPA allows use of
site-specific DOC and POC data when normalizing the BAF to organic
carbon content. One can either conduct studies to generate the
necessary site-specific data or modify the national organic carbon
database to their particular site and conditions. To facilitate the
latter, we have updated and expanded the organic carbon database used
to develop the national default POC/DOC values to enable the regulated
community to choose which values best represent their site conditions
and will provide defensible site-specific DOC and POC estimates. The
national DOC/POC database will be made available for use by all States,
Tribes, and other members of the regulated community.
5. Fish Lipid Content
Comments--A commenter stated that lipid content can affect the
results of the Gobas model used to derive national default FCMs. The
commenter noted that the model is relatively insensitive to fish lipid
content but more sensitive to benthic invertebrate lipid content. They
believed this should be considered in the development of FCMs.
Response--EPA agrees that lipid content can affect the results of
the Gobas model and is only using the Gobas model with default lipid
values to derive national BAFs when there are no data to derive a
field-measured BAF. In cases where a State or authorized Tribe has
site-specific data on fish lipid content, the revised methodology
allows input of those site-specific data to estimate bioaccumulation.
Furthermore, to facilitate the generation of site-specific lipid
values, we have updated and expanded the lipid database used to develop
the national default values based on a whole range of organisms
commonly consumed by persons in the United States. We will include
additional guidance for States and authorized Tribes on how to adapt
the national default lipid values to reflect State and local
consumption patterns. To enable such adaptions, EPA will make the raw
data available to States and authorized Tribes.
6. Use of Food Chain Multipliers (FCMs)
Comments--Several commenters stated that the use of model-derived
FCMs (Gobas 1993) to calculate a BAF from either a BCF or a
Kow (Methods 3 and 4) is inappropriate. The commenters noted
issues with several of the default input parameters (e.g., food web,
lipid, socw, temperature). The primary concern of
commentors is that Gobas model-based national default FCMs do not
account for site-specific factors that influence bioaccumulation, such
as food web structure, nor does the current use of the model account
for metabolism. Commenters expressed concern that use of default FCMs
in predictive approaches may lead to overestimates of bioaccumulation.
Some commenters preferred the use of field-based FCMs or direct use of
the Gobas model, which allows for input of site-specific data and
metabolism rates if available, rather than uses of model-derived
default FCMs.
Response--EPA is using a state-of-the-art food web model for
deriving FCMs, which incorporates the latest thinking and knowledge on
the processes occurring in aquatic food webs. Commenters suggested that
the assumptions used in constructing these models are not appropriate.
We recognize that any modeling formulation of contaminant behavior in
aquatic food webs requires simplification of a very complex biological
system in order to assemble a tractable model. These simplifications do
not imply or mean that our scientific understanding of all processes
occurring in food webs is complete. As documented in the scientific
literature, these simplifications provide reasonable model formulations
with good predictive power. The suggestion that every modeling
assumption has to be completely understood and validated under all
circumstances before using or constructing a useful modeling tool is
unreasonable. EPA has performed a detailed analysis of the importance
and sensitivities of individual input parameters for food web models
and of the overall uncertainties associated with predictions from food
web models (Burkhard 1998). We have provided a discussion in the
Bioaccumulation TSD of the Gobas model and implications that
uncertainties in their respective input parameters have on derived
FCMs. EPA has retained the use of Gobas model to derive default FCMs.
To address national versus site-specific concerns expressed by some
commenters, the methodology has been revised to separate the BAF
methodology into national and site-specific guidance. The national
methodology for deriving national BAFs retains the use of default FCMs
based on a mixed benthic/pelagic food web and national averages of
various model input values. We believe this food web is the most
broadly applicable food web encountered in nature; its use results in
FCMs that are midway between pure benthic and pure pelagic structures.
The revised guidance includes a brief discussion of the uncertainties
associated with our selection of the mixed benthic/pelagic food web. In
the site-specific guidance, the 2000 Human Health Methodology provides
guidance on which of EPA's recommended FCMs to use depending on the
situation. In addition, we encourage direct use of the Gobas model by
stakeholders so that changes could be made to the default food web
inputs to reflect site-specific factors that influence bioaccumulation,
and also encourage derivation of field-based FCMs. States and
authorized Tribes have the option to generate site-specific FCMs by
conducting site-specific field studies, reviewing published literature,
or using other scientifically defensible models.
Although several commenters criticized the national application of
the Gobas model because metabolism rate is set equal to zero, the peer
review panel acknowledged EPA's position that there are currently no
acceptable methods available to adequately determine species and
chemical-specific metabolism rates for use in the Gobas model. Because
EPA agrees that for certain chemicals metabolism can be an important
factor in bioaccumulation, the revised methodology does not use FCM-
based predictions for chemicals that are expected to be metabolized
substantially. To assist users of the 2000 Human Health Methodology in
determining for which chemicals or groups of chemicals metabolism
should be of little concern, we have developed a table of chemicals
that are not substantially metabolized or are likely very slowly
metabolized. This table has been put in the Bioaccumulation TSD. The
table is not all inclusive because there are numerous chemicals (e.g.,
hundreds of thousands in use commercially today) for which few or no
metabolism data exist, but is representative of chemicals or groups of
chemicals that are likely to be commonly encountered in aquatic
systems. When metabolism is suspected,
[[Page 66481]]
users of the 2000 Human Health Methodology might be more inclined to
use or develop field data and/or measure a BCF in the laboratory in
these situations. It should also be noted that in the future, should
appropriate chemical and species-specific metabolism data become
available, the Gobas model can incorporate it with little effort.
Finally, EPA partially agrees with commenters that certain
procedures of the 1998 draft Methodology revisions (e.g.,
Kow and FCM-predicted BAFs) might lead to overestimates of
BAFs for certain types of pollutants, such as those that are
metabolized substantially to chemical forms not addressed by the AWQC.
In response to this issue, and as discussed previously, additional
guidance and limitations have been placed on several of the procedures
in the revised methodology. However, EPA does not agree with the notion
that our methodology would lead to a general over prediction for all
BAFs. We use central tendencies where possible for all inputs in the
Gobas model, and a geometric mean BCF for chemicals that have more than
one BCF for a given trophic level. Thus, we know of no reason why
laboratory-measured BCFs multiplied by a FCM would always result in
overestimates of BAFs, or why the BSAF and Kow * FCM-
predicted BAFs applied to highly hydrophobic contaminants that do not
metabolize substantially would be biased a priori toward overestimating
BAFs. These views are supported by information in the 1998 TSD
(Exhibits 2.4.1, 2.4.3, and 2.4.6 for BSAFs), Burkhard et al. (1997)
for the Kow*FCM method, and information presented in the
Bioaccumulation TSD.
7. Fish Tissue Criteria
Comments--A few commenters suggested that for selected highly
bioaccumulative chemicals that are difficult to measure in water,
criteria based on fish tissue concentration may be more appropriate
than ambient water column concentration criteria.
Response--Regarding fish tissue criteria, EPA agrees that the
development of human health criteria for highly bioaccumulative
chemicals which are expressed in terms of tissue residues in aquatic
organisms is worthy of consideration. However, such tissue residue
criteria would still require a mechanism to relate chemical loads and
concentrations in water and sediments to concentrations in tissues of
appropriate aquatic organisms (i.e., bioaccumulation factors or
bioaccumulation models). EPA is presently exploring the feasibility of
developing tissue-based criteria and is evaluating numerous issues
associated with implementation of tissue-based criteria. At an
appropriate in the future, EPA will consider development of additional
guidance on tissue residue criteria pending the outcome of this
evaluation.
G. Literature Cited
Burkhard LP. 1998. Comparison of two models for predicting
bioaccumulation of hydrophobic organic chemicals in a Great Lakes
food web. Environ. Toxicol. Chem. 17(3):383-393.
Burkhard LP, Sheedy BR, McCauley DJ, DeGraeve GM. 1997.
Bioaccumulation factors for chlorinated benzene, chlorinated
butadienes and hexachloroethane. Environ. Toxicol. Chem. 16(8):1677-
1686.
Fisk AT, Norstrom RJ, Cymbalisty CC, Muir DCB. 1998. Dietary
accumulation and depuration of hydrophobic organochlorines:
bioaccumulation parameters and their relationship with the octanol/
water partition coefficient. Environ. Toxicol. Chem. 17(5):951-961.
Gobas FAPC. 1993. A model for predicting the bioaccumulation of
hydrophobic organic chemicals in aquatic food-webs: application to
Lake Ontario. Ecol. Model. 69:1-17.
Niimi AJ. 1985. Use of laboratory studies in assessing the behavior
of contaminants in fish inhabiting natural ecosystems. Water Poll.
Res. J. Can. 20:79-88.
Oliver BG, Niimi AJ. 1983. Bioconcentration of chlorobenzenes from
water by rainbow trout: correlations with partition coefficients and
environmental residues. Environ. Sci. Technol. 17:287-291.
Oliver BG, Niimi AJ. 1988. Trophodynamic analysis of polychlorinated
biphenyl congeners and other chlorinated hydrocarbons in the Lake
Ontario ecosystem. Environ. Sci. Technol. 22:388-397.
Russell RW, Gobas FAPC, Haffner GD. 1999. Role of chemical and
ecological factors in trophic transfer of organic chemicals in
aquatic food webs. Environ Toxicol Chem. 18:1250-1257.
Swackhamer, DL, Hites RA. 1988. Occurrence and bioaccumulation of
organochlorine compounds in fishes from Siskiwit Lake, Isle Royale,
Lake Superior. Environ Sci. Technol. 22:543-548.
USEPA (U.S. Environmental Protection Agency). 1980. Guidelines and
methodology used in the preparation of health effect assessment
chapters of the consent decree water criteria documents. Federal
Register 45:79347, Appendix 3.
USEPA (U.S. Environmental Protection Agency). 1984. Proposed
guidelines for carcinogen risk assessment. Federal Register
49:46294.
USEPA (U.S. Environmental Protection Agency). 1986a. Guidelines for
carcinogen risk assessment. Federal Register 51:33992-34003.
USEPA (U.S. Environmental Protection Agency). 1986b. Guidelines for
mutagenicity risk assessment. Federal Register 51:34006-34012.
USEPA (U.S. Environmental Protection Agency). 1986c. Total Exposure
Assessment Model (TEAM) Study: Summary and Analysis, Volume I, Final
Report. EPA/600/6-87/002a.
USEPA (U.S. Environmental Protection Agency). 1986d. Quality
Criteria for Water--1986. Office of Water Regulations and Standards,
Office of Water. Washington, DC. EPA/440/5-86/001.
USEPA (U.S. Environmental Protection Agency). 1990. Lake Ontario
TCDD Bioaccumulation Study--Final Report. USEPA, Region II. New
York, NY. EPA/822/R-94/002.
USEPA (U.S. Environmental Protection Agency). 1991a. Guidelines for
developmental toxicity risk assessment. Federal Register 56:63798-
63826.
USEPA (U.S. Environmental Protection Agency). 1991b. Technical
Support Document for Water Quality-Based Toxics Control. Office of
Water. Washington, DC. EPA/505/2-90/001.
USEPA (U.S. Environmental Protection Agency). 1992a. Guidelines for
exposure assessment. Federal Register 57:22888-22938.
USEPA (U.S. Environmental Protection Agency). 1992b. Development and
Application of a Model of PCBs in the Green Bay, Lake Michigan
Walleye and Brown Trout and Their Food Webs. Prepared by Manhattan
College, Riverdale, NY.
USEPA (U.S. Environmental Protection Agency). 1994. Water Quality
Standards Handbook and Appendices. Second edition. Office of Water.
Washington, DC. EPA/823/B-94/005a.
USEPA (U.S. Environmental Protection Agency). 1996a. Proposed
guidelines for carcinogen risk assessment. Federal Register
61:17960.
USEPA (U.S. Environmental Protection Agency). 1996b. Guidelines for
reproductive toxicity risk assessment. Federal Register 61:56274-
56322.
USEPA (U.S. Environmental Protection Agency). 1996c. Report on the
Benchmark Dose Peer Consultation Workshop. Office of Research and
Development. Washington, DC. EPA/630/R-96/011. November.
USEPA (U.S. Environmental Protection Agency). 1997a. Exposure
Factors Handbook. Office of Research and Development. Washington,
DC. EPA/600/P-95/002Fa.
USEPA (U.S. Environmental Protection Agency). 1997b. Guiding
Principles for Monte Carlo Analysis. Risk Assessment Forum.
Washington, DC. EPA/630/R-97/001.
USEPA (U.S. Environmental Protection Agency). 1997c. Policy for Use
of Probabilistic Analysis in Risk Assessment at the U.S.
Environmental Protection Agency. Risk Assessment Forum. Washington,
DC. Web site: http://www.epa.gov/ncea/mcpolicy.htm.
USEPA (U.S. Environmental Protection Agency). 1998a. Guidelines for
[[Page 66482]]
neurotoxicity risk assessment. Federal Register 63:26926.
USEPA (U.S. Environmental Protection Agency). 1998b. National
recommended water quality criteria. Federal Register 64:19781.
USEPA (U.S. Environmental Protection Agency). 1998c. Draft water
quality criteria methodology: Human health. Federal Register
63:43756.
USEPA (U.S. Environmental Protection Agency). 1998d. Ambient Water
Quality Criteria Derivation Methodology: Human Health. Technical
Support Document (TSD). Office of Water. Washington, DC. EPA-822-B-
98-005.
USEPA (U.S. Environmental Protection Agency). 1998e. National
recommended water quality criteria; republication. Federal Register
63:68354-68364.
USEPA (U.S. Environmental Protection Agency). 1999a. 1999 Guidelines
for Carcinogen Risk Assessment--Review Draft. Office of Research and
Development. Washington, DC. NCEA-F-0644. July.
USEPA (U.S. Environmental Protection Agency). 1999b. Guidance for
Conducting Health Risk Assessment of Chemical Mixtures--External
Peer Review Draft. Risk Assessment Forum. Washington, DC. NCEA-C-
0148. April.
USEPA (U.S. Environmental Protection Agency). 1999c. National
Recommended Water Quality Criteria--Correction. Office of Water.
Washington, DC. EPA-822-Z-99-001. April.
USEPA (U.S. Environmental Protection Agency). 1999d. Review of
Revised Sections of the Proposed Guidelines for Carcinogen Risk
Assessment. Science Advisory Board (1400). Washington, DC. EPA-SAB-
EC-99-015. July.
USEPA (U.S. Environmental Protection Agency). 2000a. Review and
approval of state and tribal water quality standards. Federal
Register 65:24641.
USEPA (U.S. Environmental Protection Agency). 2000b. Health
Assessment for 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) and
Related Compounds, Internal Review Draft. Office of Research and
Development. Washington, DC. EPA-600-P-001Af. February 14.
USEPA (U.S. Environmental Protection Agency). 2000c. Estimated Per
Capita Water Ingestion in the United States: Based on Data Collected
by the United States Department of Agriculture's 1994-96 Continuing
Survey of Food Intakes by Individuals. Office of Science and
Technology, Office of Water. Washington, DC. EPA-822-00-008. April.
USEPA (U.S. Environmental Protection Agency). 2000d. Estimated Per
Capita Fish Consumption in the United States: Based on Data
Collected by the United States Department of Agriculture's 1994-1996
Continuing Survey of Food Intake by Individuals. Office of Science
and Technology, Office of Water. Washington, DC. March.
Watras CJ, Bloom NS. 1992. Mercury and methylmercury in individual
zooplankton: Implications for bioaccumulation. Limnol. Oceanogr.
37(6):1313-1318.
This Notice finalizes revisions to EPA's 1980 Methodology for the
development of water quality criteria to protect human health. The
revisions reflect scientific advancements since 1980 in a number of
areas, including cancer and noncancer risk assessments, exposure
assessments and bioaccumulation. The revised Methodology provides
guidance to States, Tribes, and the public on the approach that EPA
expects to take in developing recommended human health criteria. The
revised Methodology also provides guidance to States and Tribes that
they may use in developing human health criteria as part of their water
quality standards; States and Tribes use such standards in implementing
a number of environmental programs, including setting discharge limits
in NPDES permits. The revised Methodology does not substitute for the
Clean Water Act or EPA's regulations; nor is it a regulation itself.
Thus, the revised Methodology cannot impose legally-binding
requirements on EPA, States, Tribes or the regulated community, and may
not apply to a particular situation based upon the circumstances. EPA
and State/Tribal decision-makers retain the discretion to use
different, scientifically defensible, methodologies to develop human
health criteria on a case-by-case basis that differ from this guidance
where appropriate. EPA may change the Methodology in the future through
intermittent refinements as advances in science or changes in Agency
policy occur.
This criteria Methodology incorporates scientific advancements made
over the past two decades. The use of this Methodology is an important
component of the Agency's efforts to improve the quality of the
Nation's waters. EPA believes the Methodology will enhance the overall
scientific basis of water quality criteria. Further, the Methodology
should help States and Tribes address their unique water quality issues
and risk management decisions, and afford them greater flexibility in
developing their water quality programs.
Dated: October 24, 2000.
J. Charles Fox,
Assistant Administrator for Water.
[FR Doc. 00-27924 Filed 11-2-00; 8:45 am]
BILLING CODE 6560-50-P