[Federal Register: March 12, 2003 (Volume 68, Number 48)]
[Proposed Rules]
[Page 11770-11790]
From the Federal Register Online via GPO Access [wais.access.gpo.gov]
[DOCID:fr12mr03-19]
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ENVIRONMENTAL PROTECTION AGENCY
40 CFR Part 136
[FRL-7463-1]
RIN 2040-AD53
Guidelines Establishing Test Procedures for the Analysis of
Pollutants; Procedures for Detection and Quantitation
AGENCY: Environmental Protection Agency (EPA).
ACTION: Proposed rule.
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SUMMARY: This action proposes revisions to the procedures for
determining the sensitivity of analytical (test) methods under EPA's
Clean Water Act (CWA). EPA's method detection limit (MDL) and minimum
level of quantitation (ML) are used to define test sensitivity under
the CWA. The MDL is used to determine the lowest concentration at which
a substance is detected or is ``present'' in a sample. The ML appears
in many EPA methods and has been used to describe the lowest
concentration of a substance that gives a recognizable signal, or as a
quantitation limit. The proposed revisions include clarifications and
improvements that are based on a recent EPA assessment of the MDL and
the ML and of alternative approaches for defining test sensitivity,
peer review of the Agency's assessment, and earlier stakeholder
comments on the existing MDL procedure. This proposal also revises the
definition of the MDL to reflect the proposed revisions to the
procedure. The Agency's assessment of existing EPA procedures for
determining test sensitivity and alternative approaches is also made
available for public comment in a separate notice in today's Federal
Register (see Notice of Document Availability and Public Comment Period
on the Technical Support Document for the Assessment of Detection and
Quantitation Concepts).
DATES: Comments must be postmarked, delivered by hand, or
electronically mailed on or before July 10, 2003. Comments provided
electronically will be considered timely if they are submitted
electronically by 11:59 p.m. Eastern Time on July 10, 2003.
ADDRESSES: Comments may be submitted by mail to Water Docket, U.S.
Environmental Protection Agency (4101T), 1200 Pennsylvania Avenue NW.,
Washington DC 20460, or electronically through EPA Dockets at
[[Page 11771]]
http://www.epa.gov/edocket/, Attention Docket ID No. OW-2003-0002. See
http://www.epa.gov/edocket/, Attention Docket ID No. OW-2003-0002. See
Unit C of the SUPPLEMENTARY INFORMATION section for additional ways to
submit comments and more detailed instructions.
FOR FURTHER INFORMATION CONTACT: William Telliard; Engineering and
Analysis Division (4303T); Office of Science and Technology; Office of
Water; U.S. Environmental Protection Agency; Ariel Rios Building; 1200
Pennsylvania Avenue, NW.; Washington, DC 20460, or call (202) 566-1061
or E-mail at telliard.william@epa.gov.
SUPPLEMENTARY INFORMATION:
A. Potentially Regulated Entities
EPA Regions, as well as States, Territories and Tribes authorized
to implement the National Pollutant Discharge Elimination System
(NPDES) program, issue permits that comply with the technology-based
and water quality-based requirements of the Clean Water Act (CWA). In
doing so, NPDES permitting authorities, including States, Territories,
and Tribes, make several discretionary choices when they write the
permit. These choices include the selection of pollutants to be
measured and, in many cases, limited in permits. If EPA has
``approved'' (i.e., promulgated through rulemaking) standardized
testing procedures under 40 CFR part 136 for the analysis of a given
pollutant, the NPDES permit must include one of the approved testing
procedures or an approved alternate test procedure. The testing
procedures can include a specification for detection and quantitation
levels that must be met. Therefore, entities with NPDES permits could
potentially be regulated by the proposed revisions to the detection and
quantitation procedures in this rulemaking. In addition, when an
authorized State, Territory, or Tribe certifies Federal licenses under
CWA section 401, they must use the standardized testing procedures and
meet the associated detection and quantitation levels. Categories and
entities that could potentially be regulated include:
------------------------------------------------------------------------
Examples of potentially regulated
Category entities
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State, Territorial, and Indian States, Territories, and Tribes
Tribal Governments. authorized to administer the NPDES
permitting program; States,
Territories, and Tribes providing
certification under Clean Water Act
section 401
Industry.......................... Facilities that must conduct
monitoring to comply with NPDES
permits
Municipalities.................... POTWs that must conduct monitoring
to comply with NPDES permits
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This table is not intended to be exhaustive, but rather provides a
guide for readers regarding entities likely to be regulated by this
action. This table lists the types of entities that EPA is now aware
could potentially be regulated by this action. Other types of entities
not listed in the table could also be regulated. If you have questions
regarding the applicability of this action to a particular entity,
consult the person listed in the preceding FOR FURTHER INFORMATION
CONTACT section.
B. How Can I Get Copies of This Document and Other Related Information?
1. Docket. EPA has established an official public docket for this
action under Docket ID No. OW-2003-0002. The official public docket
consists of the documents specifically referenced in this action, any
public comments received, and other information related to this action.
Although a part of the official docket, the public docket does not
include Confidential Business Information (CBI) or other information
whose disclosure is restricted by statute. The official public docket
is the collection of materials that is available for public viewing at
the Water Docket in the EPA Docket Center, EPA West Building, Room
B102, 1301 Constitution Avenue NW., Washington, DC. The EPA Docket
Center Public Reading Room is open from 8:30 a.m. to 4:30 p.m., Monday
through Friday, excluding legal holidays. The telephone number for the
Public Reading Room is (202) 566-1744, and the telephone number for the
Water Docket is (202) 566-2426.
2. Electronic Access. You may access this Federal Register document
electronically through the EPA Internet under the ``Federal Register''
listings athttp://www.epa.gov/fedrgstr/. An electronic version of the
listings athttp://www.epa.gov/fedrgstr/. An electronic version of the
public docket is available through EPA's electronic public docket and
comment system, EPA Dockets. You may use EPA Dockets at http://
www.epa.gov/edocket/
to submit or view public comments, to access the
www.epa.gov/edocket/ to submit or view public comments, to access the
index listing of the contents of the official public docket, and to
access those documents in the public docket that are available
electronically. Once in the system, select ``search,'' then key in the
appropriate docket identification number.
Certain types of information will not be placed in the EPA Dockets.
Information claimed as CBI and other information whose disclosure is
restricted by statute, which is not included in the official public
docket, will not be available for public viewing in EPA's electronic
public docket. EPA's policy is that copyrighted material will not be
placed in EPA's electronic public docket but will be available only in
printed, paper form in the official public docket. Although not all
docket materials may be available electronically, you may still access
any of the publicly available docket materials through the docket
facility identified in B.1.
For public commenters, it is important to note that EPA's policy is
that public comments, whether submitted electronically or in paper,
will be made available for public viewing in EPA's electronic public
docket as EPA receives them and without change, unless the comment
contains copyrighted material, CBI, or other information whose
disclosure is restricted by statute. When EPA identifies a comment
containing copyrighted material, EPA will provide a reference to that
material in the version of the comment that is placed in EPA's
electronic public docket. The entire printed comment, including the
copyrighted material, will be available in the public docket.
Public comments submitted on computer disks that are mailed or
delivered to the docket will be transferred to EPA's electronic public
docket. Public comments that are mailed or delivered to the Docket will
be scanned and placed in EPA's electronic public docket. Where
practical, physical objects will be photographed, and the photograph
will be placed in EPA's electronic public docket along with a brief
description written by the docket staff.
C. How and to Whom Do I Submit Comments?
You may submit comments electronically, by mail, or through hand
delivery/courier. To ensure proper receipt by EPA, identify the
appropriate docket identification number in the subject line on the
first page of your comment. Please ensure that your
[[Page 11772]]
comments are submitted within the specified comment period. Comments
received after the close of the comment period will be marked ``late.''
EPA is not required to consider these late comments. However, late
comments may be considered if time permits.
1. Electronically. If you submit an electronic comment as
prescribed below, EPA recommends that you include your name, mailing
address, and an e-mail address or other contact information in the body
of your comment. Also include this contact information on the outside
of any disk or CD ROM you submit, and in any cover letter accompanying
the disk or CD ROM. This ensures that you can be identified as the
submitter of the comment and allows EPA to contact you in case EPA
cannot read your comment due to technical difficulties or needs further
information on the substance of your comment. EPA's policy is that EPA
will not edit your comment, and any identifying or contact information
provided in the body of a comment will be included as part of the
comment that is placed in the official public docket, and made
available in EPA's electronic public docket. If EPA cannot read your
comment due to technical difficulties and cannot contact you for
clarification, EPA may not be able to consider your comment.
i. EPA Dockets. Your use of EPA's electronic public docket to
submit comments to EPA electronically is EPA's preferred method for
receiving comments. Go directly to EPA Dockets at http://www.epa.gov/
edocket
, and follow the online instructions for submitting comments.
Once in the system, select ``search,'' and then key in Docket ID No.
OW-2003-0002. The system is an ``anonymous access'' system, which means
EPA will not know your identity, e-mail address, or other contact
information unless you provide it in the body of your comment.
ii. E-mail. Comments may be sent by electronic mail (e-mail) to:
OW-docket@epamail.epa.gov, Attention Docket ID No. OW-2003-0002. In
contrast to EPA's electronic public docket, EPA's e-mail system is not
an ``anonymous access'' system. If you send an e-mail comment directly
to the Docket without going through EPA's electronic public docket,
EPA's e-mail system automatically captures your e-mail address. E-mail
addresses that are automatically captured by EPA's e-mail system are
included as part of the comment that is placed in the official public
docket, and made available in EPA's electronic public docket.
iii. Disk or CD ROM. You may submit comments on a disk or CD ROM
that you mail to the mailing address identified in Unit C.2. These
electronic submissions will be accepted in WordPerfect or ASCII file
format. Avoid the use of special characters and any form of encryption.
2. By Mail. Send an original and three copies of your comments to
Water Docket, U.S. Environmental Protection Agency (4101T), 1200
Pennsylvania Avenue NW., Washington, DC 20460, Attention Docket ID No.
OW-2003-0002.
3. By Hand Delivery or Courier. Deliver your comments to the Water
Docket Center, EPA West Building, Room B102, 1301 Constitution Avenue
NW., Washington, DC, Attention Docket ID No. OW-2003-0002. Such
deliveries are only accepted during the Docket's normal hours of
operation as identified in Unit B.1.
C. How Should I Submit CBI to the Agency?
Do not submit information that you consider to be CBI
electronically through EPA's electronic public docket or by e-mail. You
may claim information that you submit to EPA as CBI by marking any part
or all of that information as CBI (if you submit CBI on disk or CD ROM,
mark the outside of the disk or CD ROM as CBI and then identify
electronically within the disk or CD ROM the specific information that
is CBI). Information so marked will not be disclosed except in
accordance with procedures set forth in 40 CFR part 2.
In addition to one complete version of the comment that includes
any information claimed as CBI, a copy of the comment that does not
contain the information claimed as CBI must be submitted for inclusion
in the public docket and EPA's electronic public docket. If you submit
the copy that does not contain CBI on disk or CD ROM, mark the outside
of the disk or CD ROM clearly that it does not contain CBI. Information
not marked as CBI will be included in the public docket and EPA's
electronic public docket without prior notice. If you have any
questions about CBI or the procedures for claiming CBI, please consult
the person identified in the FOR FURTHER INFORMATION CONTACT section.
D. What Should I Consider as I Prepare My Comments for EPA ?
You may find the following suggestions helpful for preparing your
comments:
1. Explain your views as clearly as possible.
2. Describe any assumptions that you used.
3. Provide any technical information and/or data you used that
support your views.
4. If you estimate potential burden or costs, explain how you
arrived at your estimate.
5. Provide specific examples to illustrate your concerns.
6. Offer alternatives.
7. Make sure to submit your comments by the comment period
deadline.
8. Ensure proper receipt by EPA by identifying the appropriate
docket identification number in the subject line on the first page of
your response. It would also be helpful if you provided the name, date,
and Federal Register citation related to your comments.
Outline of Document
I. Statutory Authority
II. Purpose of This Action
III. Background
A. Analytical (Test) Methods Used for CWA Programs
B. Settlement Agreement
C. Detection, Quantitation, and Current Controversy
D. Historical Use of Detection and Quantitation Limits under the
Clean Water Act
IV. EPA's Assessment of Detection and Quantitation Concepts
A. Study Plan
B. Information and Data Used in the Assessment
C. Concepts and Procedures Included in the Assessment
D. Issues Considered during the Assessment
E. Evaluation Criteria
V. EPA's Findings and Conclusions
VI. Peer Review of EPA's Assessment
VII. Proposed Revisions to the MDL and ML
A. Definition of the Detection Limit
B. Technical Revisions to the MDL Procedure
C. Editorial Changes to the MDL Procedure
D. Definition and Procedure for Determining the Minimum Level of
Quantitation
E. Acceptance of Test Methods Employing Alternative Detection
and Quantitation Procedures
VIII. Industry Proposal
IX. Solicitation of Comments
X. Statutory and Executive Order Reviews
A. Executive Order 12866: Regulatory Planning and Review
B. Paperwork Reduction Act
C. Regulatory Flexibility Act
D. Unfunded Mandates Reform Act
E. Executive Order 13132: Federalism
F. Executive Order 13175: Consultation and Coordination with
Indian Tribal Governments
G. Executive Order 13045: Protection of Children from
Environmental Health & Safety Risks
H. Executive Order 13211: Actions that Significantly Affect
Energy Supply, Distribution, or Use
I. National Technology Transfer and Advancement Act
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XI. References
Appendix A: Definitions, Acronyms, and Abbreviations Used in This
Document
I. Statutory Authority
This action is being proposed pursuant to the authority of sections
301(a), 304(h), and 501(a) of the Clean Water Act (``CWA'' or the
``Act''), 33 U.S.C. 1311(a), 1314(h), 1361(a). Section 301(a) of the
Act prohibits the discharge of any pollutant into navigable waters
unless the discharge complies with a National Pollutant Discharge
Elimination System (NPDES) permit issued under section 402 of the Act.
Section 304(h) of the Act requires the Administrator of the EPA to
``promulgate guidelines establishing test procedures for the analysis
of pollutants that shall include the factors which must be provided in
any certification pursuant to [section 401 of this Act] or permit
application pursuant to [section 402 of this Act].'' Section 501(a) of
the Act authorizes the Administrator to ``prescribe such regulations as
are necessary to carry out this function under [the Act].'' EPA
publishes analytical test method regulations for use in CWA programs at
40 CFR part 136. The Administrator has made these test methods
applicable to monitoring and reporting of NPDES permits (40 CFR 122.21,
122.41, 122.44, and 123.25), and implementation of the pretreatment
standards issued under section 307 of the Act (40 CFR 403.10 and
403.12).
II. Purpose of This Action
EPA recently completed an assessment of procedures for determining
the sensitivity of analytical test methods (i.e., procedures for
determining detection and quantitation) and their application to Clean
Water Act Programs. That assessment was conducted pursuant to a
settlement agreement with the Alliance of Automobile Manufacturers, et
al. (See III.B. below for details.) The assessment is contained in a
document entitled, Technical Support Document for the Assessment of
Detection and Quantitation Concepts or ``Assessment Document'' (EPA
821-R-03-005, February, 2003). A draft of the Assessment Document was
peer-reviewed in August 2002 in accordance with EPA peer review
guidelines. Following peer review, EPA incorporated peer review
comments into the Assessment Document. EPA is providing an opportunity
for public review and comment on the assessment and the Assessment
Document through this notice and also in a separate notice in this
Federal Register (see Notice of Document Availability and Public
Comment Period on the Technical Support Document for the Assessment of
Detection and Quantitation Concepts).
Based on findings from the assessment, EPA is proposing revisions
to the method detection limit procedure codified at 40 CFR part 136,
Appendix B and is seeking comment on the revisions proposed in this
notice. EPA also is proposing to revise the definition of ``Detection
limit'' at 40 CFR 136.2 and to add a definition of the ``Minimum level
of quantitation (ML)'' for consistency with the proposed revisions to
Appendix B.
III. Background
A. Analytical (Test) Methods Used for CWA Programs
Section 304(h) of the Clean Water Act requires that the EPA
Administrator ``promulgate guidelines establishing test procedures for
the analysis of pollutants'' to be monitored and regulated under the
National Pollutant Discharge Elimination System (NPDES). EPA proposes
and promulgates test methods at 40 CFR part 136 in accordance with
section 304(h). The approved test methods have been drawn from a
variety of sources, including methods developed by commercial vendors,
EPA and other government agencies, as well as methods from voluntary
consensus standards bodies (VCSBs), such as the American Public Health
Association (APHA), the Water Environment Federation (WEF), and the
American Water Works Association (AWWA), which jointly publish Standard
Methods for the Examination of Water and Wastewater; the Association of
Official Analytical Chemists (AOAC-International); and the American
Society for Testing and Materials (ASTM International).
Among considerations for approval of a test method at 40 CFR part
136 are the demonstrated performance characteristics of precision,
bias, and sensitivity (i.e., detection and quantitation). EPA generally
evaluates each of these characteristics to determine if the test method
will yield results at concentrations of concern that are reliable
enough to meet EPA needs for permitting and compliance monitoring under
the CWA. Detection and quantitation limits have been among the most
controversial of these characteristics, particularly among members of
the regulated community.
B. Settlement Agreement
On June 8, 1999, EPA published a final rule adding EPA Method 1631,
Revision B: Mercury in Water by Oxidation, Purge and Trap, and Cold
Vapor Atomic Fluorescence Spectrometry (Method 1631B) to the
``Guidelines Establishing Test Procedures for the Analysis of
Pollutants'' under section 304(h) of the Clean Water Act. This method
was developed specifically to measure concentrations of mercury at low
(i.e., ambient water quality criteria) levels. Following promulgation,
the Alliance of Automobile Manufacturers, the Chemical Manufacturers
Association, and the Utility Water Act Group (``Petitioners'') and the
American Forest and Paper Association (``Intervenor'') filed a lawsuit
challenging the method. (Alliance of Automobile Manufacturers, et al.
v. EPA, No. 99-1420 (D.C. Cir.)). The challenge addressed specific
aspects of EPA Method 1631 as well as the general procedures used to
establish the method detection limit (MDL) and the minimum level of
quantitation (ML) specified in the method. On October 19, 2000, EPA
entered into a settlement agreement with the Petitioners and Intervenor
(the ``settlement agreement''). The settlement agreement included six
clauses. EPA has already satisfied the requirements of clauses 1
through 5, which addressed clarification and revision of specific
method procedures and requirements. This proposal partially fulfills
the requirements of clause 6 of the settlement agreement, which
addresses procedures for determining the sensitivity of analytical test
methods.
Clause 6 provides for EPA to assess existing Agency and alternative
procedures for determining detection and quantitation limits under the
Clean Water Act and to sign a notice for publication in the Federal
Register on or before February 28, 2003, inviting public comment on the
assessment. The assessment is to include, at a minimum, evaluation of
the ``Definition and Procedure for Determination of the Method
Detection Limit'' published at 40 CFR part 136, Appendix B and used in
Method 1631, and evaluation of the corresponding ``minimum level'' of
quantitation procedures.
Clause 6 further provides for EPA to submit its assessment to
formal peer review by experts in the field of analytical chemistry and
in the statistical aspects of analytical data interpretation. EPA
conducted peer review of its assessment in August 2002. A summary of
the results of the peer review is provided in section VI of this
proposal; the peer reviewers' comments and EPA's responses are included
in the docket for this proposal. As stipulated in the settlement
agreement, EPA
[[Page 11774]]
provided the draft Assessment Document to the Petitioners and
Intervenor for concurrent review and comment in August 2002. Their
comments are also included in the docket for this proposal.
Finally, EPA agreed to invite public comment on the assessment for
a period of no less than 120 days and to sign a notice taking final
action on the assessment on or before September 30, 2004. Elsewhere in
today's Federal Register, EPA is publishing a notice of availability of
the Assessment Document, titled ``Technical Support Document for the
Assessment of Detection and Quantitation Concepts,'' and announcing a
120-day comment period on it.
C. Detection, Quantitation, and Current Controversy
Generally speaking, a detection limit is the lowest concentration
or amount of a substance that allows for differentiation between a
sample that contains the substance and one that does not. A
quantitation limit is the lowest concentration or amount of a substance
that can be measured with some stated level of confidence. Establishing
such detection and quantitation limits generally involves the
application of statistics and chemistry expertise and judgement. The
fact that scientific judgement is involved in the detection and
quantitation decision is evidenced by the continuing debate on this
subject; the number of different terms currently in use by different
organizations; the number of concepts and procedures that have been
advanced by different organizations to define or determine the
detection and quantitation capabilities of analytical test methods; and
the fact that there is no general consensus among various government
agencies, method developers, or scientific organizations on a single
detection and quantitation approach. EPA estimates that more than 50
different terms have been used in published analytical test methods to
describe detection and quantitation capabilities of test methods and,
in many instances, the same term is used by different organizations to
mean different things.
Nearly all of the approaches advanced to date fall into one of two
main categories: (1) Those that assume measurement error is constant or
effectively constant in the low concentration range and are, therefore,
based on the error observed in replicate measurements made at a single
low concentration, and (2) those that assume measurement error varies
as a function of concentration and are, therefore, based on the error
observed in replicate measurements gathered in the region of detection
and quantitation. Examples of the first category (referred to as the
``single concentration approach'' or ``constant error model'') include
those first advanced by Lloyd Currie (1968) and later adopted in
various forms by the American Chemical Society (ACS), the International
Organization for Standardization (also known as ``ISO''), the
International Union of Pure and Applied Chemistry (IUPAC), and EPA.
Examples of the latter category (the ``variable error model'') were
adopted in various forms by the U.S. Army Toxic and Hazardous Materials
Agency (USATHAMA, now the U.S. Army Environmental Center, or USAEC) and
ASTM International. The two categories represent two somewhat different
conceptual approaches to the problem of assessing detection and
quantitation capabilities. Both approaches require estimates of
measurement variability in the low concentration range, but the
philosophy behind the first category is based on direct measurement of
variability at a fixed concentration in the concentration region most
relevant to the problem. The philosophy behind the second category is
based on the concept that measurement variability throughout the low
end of the measurement range is relevant to the problem of setting
detection and quantitation limits. The methodology used in implementing
procedures in the second category involves statistical estimation
methods that allow data collected throughout the low end of the range
to contribute to estimation of measurement variability in detection and
quantitation region.
There are also differences in the experimental procedures used to
determine detection and quantitation limits. Again, these tend to fall
into two categories. The first category of single-laboratory detection
limits uses data from an experiment in a single laboratory to estimate
detection limits. The second category of multi-laboratory detection
limits uses data from experiments from multiple laboratories to
estimate detection limits. The rationale for the latter proposal is
that actual measurement sensitivity varies among laboratories,
regardless of the approach used to estimate the sensitivity of a given
method. The Interlaboratory Detection Estimate (IDE) and the
Interlaboratory Quantitation Estimate (IQE) adopted by ASTM
International is an example of such an approach. Although EPA's MDL
procedure does not incorporate specific procedures to account for
multiple laboratory variability, EPA nonetheless has accounted for this
variability during method validation as described in Section D.1 below.
D. Historical Use of Detection and Quantitation Limits Under the Clean
Water Act
The procedure for estimating the MDL was originally published in
1981 by staff at EPA's environmental research laboratory in Cincinnati,
Ohio (Glaser, et al., 1981). The MDL is based on the constant error
model described by Currie (1968). EPA promulgated the procedure for
determining the MDL for use in CWA programs on October 26, 1984 (49 FR
43234).
The ML was originally proposed on December 5, 1979 (44 FR 69463),
in footnotes to Table 2 of EPA Method 624 and to Tables 4 and 5 of EPA
Method 625. Between 1980 and 1984, EPA developed Methods 1624 and 1625
and included the ML in similar tables in those two methods. When these
four methods were promulgated for use in CWA programs on October 26,
1984 (49 FR 43234), EPA replaced the MLs in Methods 624 and 625 with
MDLs, and retained the MLs in Methods 1624 and 1625. Unlike the MDL,
there have been changes to the definition of the ML over the years. For
example, the term ``recognizable signal'' has been used instead of
``recognizable mass spectra'' for non-GC/MS methods.
Since 1984, the MDL and ML have been used in a variety of ways by
analytical laboratories, permitting authorities, and regulatory
communities. The three most significant uses of the MDL are described
below, along with some concerns with those uses.
1. Method Development
The primary purpose of the MDL and ML is to characterize the
sensitivity of a particular test method for a particular pollutant.
Information about method sensitivity is critical when deciding which
method is needed to accomplish a specific measurement objective.
The MDLs published in some EPA methods have been criticized because
they are based on the performance of a single laboratory that may not
reflect the capabilities of the laboratory community. EPA has responded
to this criticism in recent years by gathering MDL information from
multiple laboratories. During development of several analytical
methods, EPA's Office of Science and Technology addressed the issue by
using single laboratory studies to develop an initial estimate of the
MDL for each analyte and then verified these MDLs in interlaboratory
[[Page 11775]]
studies or in additional single-laboratory studies at other facilities.
For example, when EPA initially drafted Method 1631 for measurement of
mercury, EPA estimated the MDL to be 0.05 ng/L, based on results
produced by a contract research laboratory. Additional single-
laboratory studies suggested that the MDL should be raised to 0.2 ng/L
to better reflect existing capabilities of the laboratory community.
During EPA's interlaboratory study for Method 1631, twelve participant
laboratories were asked to conduct MDL studies. Each laboratory
obtained an MDL less than 0.2 ng/L, the value published in the
promulgated version of Method 1631.
The ML has been used in the 1600-series of EPA chemical methods
promulgated for use under the CWA since 1984 as an additional means to
characterize method sensitivity, establish the lower end of the
calibration range, and serve as a quantitation limit in those methods.
Although its use has thus far been limited to the 1600-series methods,
the ML concept is applicable to any analytical procedure to which the
MDL can be applied under the CWA.
2. Demonstrating Laboratory Performance
The MDL also has been used as a means of demonstrating laboratory
capability or performance. For example, a laboratory often publishes
results of an MDL study to advertise its ability to detect a pollutant
at a low level. Similarly, a laboratory client or a certification
program may require that a laboratory demonstrate its ability to
achieve a specified MDL using a particular method.
EPA also has used MDLs in approved EPA CWA methods (i.e.,
promulgated at 40 CFR part 136) to provide a standard for allowing
increased flexibility and encouraging advances in technology. Under
EPA's CWA Alternate Test Procedures (ATP) program and in EPA's
performance-based methods, a laboratory is permitted to modify certain
aspects of approved method procedures provided that it is able to
achieve an MDL that is less than or equal to one-third the regulatory
compliance limit or less than or equal to the MDL specified in the
approved method, whichever is greater (see section 9.0 of EPA Method
1631, for example).
3. Use of the MDL and ML in Clean Water Act Programs
Both the MDL and ML have been used as reporting limits for a
variety of studies and monitoring efforts under the CWA. For example,
EPA often uses the MDL as a reporting threshold in surveys designed to
determine levels of human exposure from consumption of water or fish
under the CWA in order to characterize health risks from a variety of
pollutants. In recent years, EPA has used the ML as the reporting limit
in setting numeric limits for effluent guidelines limitations. EPA
recommended in a 1994 draft guidance document that the ML be included
in a National Pollutant Discharge Elimination System (NPDES) permit as
a footnote to the water quality-based effluent limit (WQBEL) when the
WQBEL is below either the MDL or ML of the most sensitive method. (See
U.S. EPA Draft National Guidance for the Permitting, Monitoring, and
Enforcement of Water Quality-based Effluent Limitations Set Below
Analytical Detection/Quantitation Levels, 1994.) This 1994 draft
guidance document was very controversial and was never finalized.
Because individual States are responsible for implementation and
enforcement of NPDES permits, use of the MDL and ML in the NPDES
program varies among the States.
4. Concerns Regarding Use of the MDL
Over the years, a number of concerns have been raised about the MDL
procedure. Some of these concerns are technical in nature (e.g.,
selection of appropriate spiking levels and treatment of outliers),
while others focus on implementation (e.g., use of the MDL as a
regulatory compliance limit). As part of EPA's assessment of detection
and quantitation limits, the Agency identified and investigated a
number of issues, including concerns that had been presented to the
Agency by a variety of sources (e.g., commercial laboratories,
permittees, State laboratory and permitting authorities, EPA and other
Federal laboratories, and others). Section IV.D of this proposal
highlights the most significant issues addressed during the recent
assessment. A comprehensive discussion of these issues is provided in
the Assessment Document that is available in the docket supporting
today's proposed rule and noticed elsewhere in today's Federal Register
for public comment.
IV. EPA's Assessment of Detection and Quantitation Concepts
EPA first began a comprehensive assessment of detection and
quantitation limits in the mid-1990s as concerns about the increased
use of water quality-based permitting began to push permit limits for
many pollutants below the measurement capabilities of some laboratories
for a number of environmental chemistry methods. One of the key areas
of concern centered on the nature of measurement error in the region of
detection and quantitation. Because EPA was not aware of studies that
included replicate testing across or within the vicinity of this
region, EPA focused its early efforts on developing such data, first
with a single-laboratory study of measurement error using inductively
coupled plasma-mass spectrometry (ICP-MS) techniques, and later with a
similar single-laboratory study of measurement error using 10 different
analytical techniques commonly used in Clean Water Act monitoring
programs.
The October 2000 settlement agreement described in section III.B.
of this preamble committed EPA to a fixed timetable and established
specific milestones for completing its assessment. The general approach
used in the Agency's assessment of detection and quantitation concepts
and procedures is summarized below. Additional details concerning the
assessment are presented in the Assessment Document that is available
in the public docket supporting this proposed rule. EPA is also
providing an opportunity for public review and comment on this
assessment and the Assessment Document in a separate notice in today's
Federal Register (see Notice of Document Availability and Public
Comment Period on the Technical Support Document for the Assessment of
Detection and Quantitation Concepts).
A. Study Plan
In December of 2001, EPA produced a draft Plan for the Assessment
of Detection and Quantitation Limits Under Section 304(h) of the Clean
Water Act. The December 2001 plan described roles and responsibilities
for implementing the plan, provided a background discussion of
detection and quantitation limit concepts, and outlined a series of
events necessary to support EPA's assessment of detection and
quantitation concepts and procedures as required to comply with the
terms and schedules set forth in Clause 6 of the settlement agreement.
The draft plan was circulated for review by EPA staff, the
Petitioners and Intervenor, and external peer reviewers. The external
peer review was performed in accordance with EPA's Science Policy
Council Handbook--Peer Review, 2nd Edition (EPA 100-B-00-001, December
2001; the ``Peer-review Handbook''). EPA evaluated the comments and
recommendations provided by reviewers and, where appropriate,
integrated these comments
[[Page 11776]]
into a revised version of the Plan for the Assessment of Detection and
Quantitation Limits Under Section 304(h) of the Clean Water Act (EPA
821-R-02-010, April, 2002; the ``study plan''). The study plan is
included in the docket for this proposal, along with the peer review
comments and the Agency's response to them..
B. Information and Data used in the Assessment
In 1997 and 1998, EPA searched the published literature to identify
documents that discussed detection and quantitation concepts and
procedures. EPA conducted a follow-up search in 2001. The principal
goal of these efforts was to identify concepts, procedures, and issues
that should be considered by EPA during its assessment. EPA identified
more than 100 documents describing detection and quantitation concepts
and issues and has included a list of these documents in the docket
supporting this proposed rule. Additional information concerning the
literature search is presented and discussed in the Assessment
Document.
EPA initially hoped to identify a large body of data containing a
sufficient number of results that were generated at, below, and above
the region of interest (i.e., at concentration levels targeting limits
of detection and quantitation). EPA determined, however, that few such
data sets exist. EPA identified six useful data sets for fully
evaluating measurement variability in the range of analytical detection
and quantitation. These included three data sets generated by EPA
expressly for the purpose of characterizing measurement variability in
the region of interest and three data sets suggested by the Petitioners
and Intervenor. Although the Petitioners and Intervenor suggested other
data sets, EPA found that these data sets either did not include a
sufficient number of data results that were at, below, and above the
region of detection and quantitation to yield information for the
assessment or that the data included in the data sets were of
questionable validity. These data, and EPA's decisions regarding the
data, are discussed in the Assessment Document.
As noted above, three of these studies were conducted by EPA for
the purpose of evaluating the relationship between measurement
variation and concentration. In these studies, replicate measurements
from each combination of analyte and measurement technique (i.e.,
analytical method) were produced by a single laboratory over a wide
range and large number of concentrations. A fourth data set was
developed as part of a study conducted by the American Automobile
Manufacturers Association (AAMA) for the purpose of estimating a
quantitation value based on a concept called the alternative minimum
level that had been described in the literature (Gibbons et al., 1997).
In that study, replicate samples were measured at a limited number of
concentrations by multiple laboratories. The final two data sets were
jointly gathered by EPA and the Electric Power Research Institute
(EPRI) to support interlaboratory validation of EPA Methods 1631 and
1638.
Additional details concerning each of these studies are provided in
the Assessment Document available in the docket supporting this
proposed rule. Data from these studies also are available in the
docket.
C. Concepts and Procedures Included in the Assessment
As mentioned earlier in this document, EPA identified numerous
terms that have been used to describe the sensitivity of a particular
method or instrument. Examples of these terms are analytical detection
limit, lower limit of detection, limit of sensitivity, minimum
detectable quantity, system detection limit, and approximate detection
limit. For its assessment, EPA considered detection and quantitation
terms, concepts, or procedures advanced in the published literature and
by various EPA offices, the American Chemical Society (ACS), the
International Union of Pure and Applied Chemistry (IUPAC), the
International Organization for Standardization (ISO), ASTM
International, industry groups, and others. EPA found that most of the
terms or concepts considered have no corresponding definition or
procedure for calculating a value, and it may be that these terms
reflect the method developer's estimate of the lowest concentration of
a substance that a test method is capable of measuring. EPA did not
evaluate any such terms in the assessment. EPA also did not consider
terms that do not reflect the entire measurement process (such as the
``Instrument Detection Limit''), concepts that are uniquely designed
for a single program (such as the ``Contract Required Detection Limit''
used in the Superfund Contract Laboratory Program), or concepts no
longer advanced by the originating organization (such as the
``Compliance Monitoring Detection Limit'' and the ``Alternative Minimum
Level'').
After eliminating terms and concepts for the reasons described
above, EPA focused its assessment on four sets of concepts that are
widely referenced and generally reflect the diversity of concepts
advanced to date. These include (1) The EPA MDL and ML used under CWA
programs, (2) the Interlaboratory Detection Estimate (IDE) and
Interlaboratory Quantitation Estimate (IQE) adopted by ASTM
International, (3) the Limit of Detection (LOD) and Limit of
Quantitation (LOQ) adopted by the American Chemical Society (ACS), and
(4) the Critical Value (CRV), Minimum Detectable Value (MDV) and Limit
of Quantification (LOQ) adopted by the International Union of Pure and
Applied Chemistry (IUPAC) and the International Organization for
Standardization (ISO). Although the ACS, IUPAC and ISO concepts are
functionally similar to EPA's MDL and ML, these organizations have not
developed detailed procedures for calculating detection and
quantitation values. Only the EPA and ASTM concepts are supported by
detailed procedures for calculating detection and quantitation values.
Without such procedural details, the ACS, IUPAC and ISO concepts are
unlikely to be useful for establishing detection and quantitation
limits in analytical methods for use in CWA programs. Therefore, the
discussion below addresses the EPA and ASTM concepts only. Results of
EPA's evaluation of the additional concepts are discussed in detail in
the Assessment Document included in the docket supporting this proposed
rule.
1. Method Detection Limit (MDL) and Minimum Level (ML) of Quantitation
As discussed in section III.D of this document, the MDL is based on
the constant error model proposed by Currie in 1968 and was initially
promulgated in 1984 for use in CWA programs. The MDL and ML are
supported by a procedure that involves the analysis of at least seven
replicate samples containing the target analyte(s) at an estimate of
the detection limit. Determination of the MDL is based on
multiplication of the standard deviation among the replicate
measurements by the 99th percentile of a t-distribution with n-1
degrees of freedom. The ML is also based on the constant error model
proposed by Currie in 1968. The ML is derived by multiplying the
standard deviation of the replicate measurements by 10. The primary
differences between the MDL, ML, and detection and quantitation limit
concepts first proposed by Currie are that (1) The MDL and ML are
supported by detailed procedures for implementing the concepts, and (2)
the EPA CWA procedures extend Currie's proposed replicate measurements
of a blank with replicate measurements of reagent water
[[Page 11777]]
(or other reference matrix) to which a small amount of the analyte is
added. This latter difference results from the fact that the concepts
developed by Currie assume that measurements on blank samples will
produce a signal that can be used to estimate measurement variability.
This is the case with radiochemistry analyses, where there is usually
some background radiation that produces a response in the analysis of a
blank sample. For many other types of environmental analyses, the
analysis of a blank sample produces no instrumental response. Thus, the
EPA CWA MDL procedure involves adding the analyte to a reference matrix
(e.g., a blank sample) at low concentrations to ensure that a response
is produced.
2. Interlaboratory Detection Estimate (IDE) and Interlaboratory
Quantitation Estimate (IQE)
The IDE was approved by ASTM International's Committee D 19 for
Water in 1997, as ASTM Designation 6091-97: Standard Practice for 99%/
95% Interlabortory Detection Estimate (IDE) for Analytical Methods with
Negligible Calibration Error. Subsequently, members of ASTM Committee D
19 developed the interlaboratory quantitation estimate (IQE) that was
approved in 2000 as ASTM Designation D 6512-00: Standard Practice for
Interlaboratory Quantitation Estimate. The IDE and IQE concepts are
based on the variable error model and include procedures that require
that data gathered in a formal study of a method be used to select from
one of four possible models of the interlaboratory error and
concentration. The possible models include: the ``constant model,''
applicable to both the IDE and IQE, in which the interlaboratory
standard deviation does not change with concentration; the ``straight-
line model,'' applicable to both the IDE and IQE, in which the
interlaboratory standard deviation is a linear function of
concentration; the ``exponential model'' applicable to the IDE, in
which the interlaboratory standard deviation is an exponential function
of concentration; and the ``hybrid model'' applicable to the IQE, in
which the interlaboratory standard deviation has both additive
(constant) and multiplicative (linear) components that follow the model
of Rocke and Lorenzato (1995). Such studies involve samples
representing at least five different concentration levels and analyzed
in a minimum of six (required) to ten (recommended) laboratories. The
ASTM procedures are also designed to take into account all possible
sources of variability, including interlaboratory variability, when
estimating detection and quantitation limits. As a result, the IDE and
IQE generally produce higher limits than are produced using other
procedures.
D. Issues Considered During the Assessment
In performing the assessment, EPA identified a number of
statistical and analytical chemistry issues that should be considered
when evaluating detection and quantitation limit concepts and
procedures in general, and in the specific context of Clean Water Act
applications. The issues considered include six specific issues raised
by the Petitioners and Intervenor, as well as issues identified by EPA
staff, peer reviewers, and others. The six issues raised by the
Petitioners are: Criteria for selection and appropriate use of
statistical models; methodology for parameter estimation; statistical
tolerance and prediction; criteria for design of detection and
quantification studies, including selection of concentration levels
(``spiking levels''); interlaboratory variability; and incorporation of
elements of probability design.
Some of the significant additional issues considered by EPA in its
assessment include: Matrix effects; minimization of false positives and
false negatives; cost and ease of implementation; and how well
detection and quantitation limits published in methods reflect
individual laboratory capability. These and other issues considered by
EPA are identified and discussed in Chapter 3 of the Assessment
Document.
E. Evaluation Criteria
After identifying and considering the issues, EPA developed six
evaluation criteria that reflect EPA's views concerning the issues.
These six criteria formed the primary basis for evaluating the ability
of each detection and quantitation limit approach identified in section
III.C. above to meet EPA needs under the Clean Water Act. A complete
discussion of these criteria and EPA's assessment of each approach
against these criteria is provided in the Assessment Document that is
available in the docket supporting this proposed rule. The six criteria
are summarized below.
Criterion 1: The detection and quantitation limit approaches should
be scientifically valid. In evaluating this criterion, EPA considered
the following factors: (1) Whether the concept can be (and has been)
tested; (2) whether the concept has been subjected to peer review and
publication; (3) whether the error rate associated with the concept or
methodology is either known or can be estimated; (4) whether standards
exist and can be maintained to control the concept's operation (i.e.,
it is supported by well-defined procedures for use); and (5) whether
the concept has attracted (i.e., achieved) widespread acceptance within
a relevant scientific community.
EPA believes that these considerations are helpful for
demonstrating the scientific validity of a detection or quantitation
concept.
Criterion 2: The approach should address demonstrated expectations
of laboratory and method performance, including routine variability.
EPA believes that the detection and quantitation limit procedures
should be capable of providing a realistic expectation of laboratory
performance. In evaluating different approaches against this criterion,
EPA considered the sources of variability captured by the procedure and
the degree to which the statistics that underlie the procedure
realistically reflect these sources.
Criterion 3: The approach should be supported by a practical and
affordable procedure that a single laboratory can use to evaluate
method performance. Ideally, any required procedure for calculating
analytical method sensitivity should be simple, complete, and cost-
effective to implement. The laboratories that can be expected to use
detection and quantitation procedures will range from large
laboratories and laboratory chains with a wide range of technical
capability to small laboratories operated by one or a few people with a
limited set of statistical or analytical skills. If a procedure is
complicated, it will be, generally, more error prone in its use.
Similarly, if a procedure requires investment of extensive resources
that cannot be billed to a client, laboratories will have a
disincentive to use the procedure. Therefore, if EPA wishes to
encourage the development and use of innovative techniques that improve
measurement performance or lower measurement cost, the Agency should
consider practicality and affordability as significant, if not co-
equal, considerations to scientific validity.
Criterion 4: The detection level approach should identify the
signal or estimated concentration at which there is 99% confidence that
the substance is actually present when the analytical method is
performed by experienced staff in a well-operated laboratory. Any
approach to developing detection limits should be capable of providing
regulators, the regulated community, and data users with confidence
that a pollutant reported as being present really is present.
Historically, nearly
[[Page 11778]]
every detection limit approach has set the criterion for detection at
99 percent confidence (i.e., the lowest level at which a pollutant will
be detected with a probability of 99 percent). This criterion results
in the probability of a false positive; i.e., that a pollutant will be
stated as being present when it is not really present (a Type I error),
of one percent.
Criterion 5: The quantitation limit approach should identify the
concentration that gives a recognizable signal that is consistent with
the capabilities of the method when a method is performed by
experienced staff in well-operated laboratories. Measurement
capabilities among laboratories vary depending on a number of factors,
including, but not limited to, instrumentation, training, and
experience. Similarly, measurement capabilities among different
analytical methods vary depending on a number of factors, including the
techniques and instrumentation employed and the clarity of the method
itself. Historical approaches to recognizing laboratory capabilities in
establishing detection and quantitation limits have varied between two
extremes of establishing the limit in a state-of-the-art research
laboratory to reflect the lowest possible limit that can be achieved,
and establishing the limit based on statistical prediction intervals
calculated from a large number of laboratories with varying levels of
experience, instrumentation and competence. Generally, use of the
former has been employed to serve as a goal or performance standard to
be met by other laboratories, whereas use of the latter treats the
limit, not as a performance standard that needs to be met by each
laboratory, but rather as a characterization of the future performance
of the entire universe of laboratory capabilities at the time of method
development. Rather than using one of these two extremes, EPA prefers
to establish a quantitation limit at a concentration that is achievable
with a defined level of confidence in well-operated laboratories.
Criterion 6: Detection and quantitation approach should be
applicable to the variety of decisions made under the Clean Water Act,
and should support State and local obligations to implement measurement
requirements that are at least as stringent as those set by the Federal
Government. The Clean Water Act requires EPA to conduct, implement, and
oversee a variety of data gathering programs. These programs include,
but are not limited to, surveys to monitor changes in ambient water
quality, screening studies to identify pollutants of concern, data
gathering to support effluent guidelines, environmental assessments to
establish water quality standards, and studies to evaluate human health
and environmental risks under the Clean Water Act. In addition, EPA
should be able to apply detection and quantitation limits to
permitting, quality control in analytical laboratories, method
promulgation, and other uses of the 40 CFR part 136 methods.
V. EPA's Findings and Conclusions
As noted previously, EPA considered four sets of detection and
quantitation limit approaches advanced by EPA, ASTM International, ACS,
and both ISO and IUPAC. Each approach was assessed against the suite of
criteria described above for use under the Clean Water Act. The EPA
approaches (i.e., the MDL and ML) and the ASTM International approaches
(i.e., the IDE and IQE) are supported by clearly defined procedures for
implementing the concepts. Neither the ACS nor the ISO/IUPAC approaches
are supported by detailed procedures for implementation; this lack of
supporting procedures was reflected in the outcome of EPA's overall
assessment. Briefly, EPA found that (1) no single pair of detection and
quantitation limit concepts perfectly meets EPA's criteria for use
under the Clean Water Act, (2) the MDL and ML most closely meet EPA's
criteria, and (3) minor revisions and clarifications to the MDL and ML
would allow both concepts to fully meet the Agency's needs under the
CWA. Details of these revisions and clarifications are described in
section VII of this proposed rule. EPA also found that, although the
IDE and IQE procedures may be acceptable for establishing detection and
quantitation values derived from interlaboratory validation studies,
the complexity and subjectivity of the procedures, along with their
inability to address individual laboratory performance, make them
unsuitable as the primary means of establishing sensitivity under the
Clean Water Act. However, EPA believes that the IDE and IQE can be used
to establish sensitivity under certain conditions. EPA would be willing
to consider and approve under 40 CFR part 136, new test methods that
include the IDE and IQE. Details of EPA's findings are provided in the
Assessment Document that is available in the docket supporting this
proposed rule.
VI. Peer Review of EPA's Assessment
In August 2002, EPA conducted a peer review of its assessment as
presented in a draft Technical Support Document (draft Assessment
Document). The peer review was performed in accordance with EPA's peer
review policies, which are described in the Science Policy Council
Handbook (EPA 100-B-00-001), and performed by two experts in the field
of analytical chemistry and two experts in the statistical aspects of
analytical data interpretation. Reviewers were provided with a draft
copy of EPA's Assessment Document, copies of all data evaluated in the
assessment, statistical programs used to analyze the data, and copies
of the detection and quantitation approaches evaluated.
In the charge to the peer reviewers, EPA requested a written
evaluation of whether the assessment approach described by EPA is valid
and of the conceptual soundness of the assessment. Reviewers also were
asked to consider and address eight specific questions pertaining to
the adequacy of the concepts and procedures, the issues considered, the
evaluation criteria developed by EPA, EPA's assessment and conclusions,
the data used to perform the assessment, suggested improvements to the
procedures discussed, and EPA's consideration of interlaboratory vs.
intralaboratory issues. A copy of all materials associated with the
peer review, including the peer review charge, the materials provided
to the peer reviewers for review, complete copies of the peer
reviewers' comments, and detailed EPA responses to each of the comments
is provided in the docket supporting this proposed rule.
The comments from the peer reviewers were generally supportive of
EPA's assessment and its presentation of the assessment in the draft
Assessment Document. The peer reviewers stated that EPA's assessment of
detection and quantitation concepts appears valid based on the
evaluation criteria and is consistent with the Data Quality Act and
EPA's Quality System. The peer reviewers stated further that the
detection and quantitation concepts and procedures considered, the
issues addressed, and the evaluation criteria developed based on those
issues are sufficiently complete and adequate. Although two of the four
peer reviewers believe that the use of interlaboratory measurements is
important for a general understanding of the laboratory communities'
capabilities, they also believe that the MDL and ML are more
appropriate to address the issues that
[[Page 11779]]
EPA must consider in support of a permittee's CWA requirements. These
commenters concluded that EPA's approach between inter- and intra-
laboratory studies is balanced and reasonable. Overall, the peer
reviewers supported the continued use of the MDL and ML procedures,
almost to the exclusion of the other approaches. The most notable
exception was a suggestion that EPA consider abandoning the
``traditional'' concept of a quantitation limit, such as the ML, and
instead consider that any measured result reported with an associated
estimate of measurement precision is a quantifiable value. Reviewers
stated, however, that use of the ML is practical if EPA desires to
establish a quantitation limit.
Although the peer reviewers were generally supportive of the
assessment and EPA's current approach to detection and quantitation
under the CWA, they had some recommendations for improvement to the
Agency's assessment and to the MDL procedure. The reviewers suggested
that EPA consider the following: (1) Providing additional references;
(2) expanding the discussion of outliers; (3) establishing a repository
of reference materials that demonstrate the ability to handle
interferences and low level detection; (4) making minor modifications
to Evaluation Criterion 4 (i.e., edit to reflect equivalence to an
implementation of Currie's critical level); (5) clarifying the MDL
confidence interval calculations discussed in Chapter 5 of the
Assessment Document; and (6) enhancing the focus on the impact of
operational procedures (quality control) in method performance. The
Assessment Document available in the docket supporting today proposed
rule addresses each of these suggestions.
The peer reviewers also suggested the following improvements to the
MDL procedure: (1) Provide clarification to indicate that blank samples
can be used to estimate the MDL if those blanks generate a signal; (2)
revise the language in Step 1 of the MDL procedure to address certain
common misunderstandings (e.g., strengthen the discussion of the
selection of the spiking level used for the MDL study); and (3) specify
that the spike level used to establish the MDL should not be more than
a factor of three times greater than the calculated MDL. The first two
suggestions from the peer reviewers regarding improvements to the MDL
procedure, have been included in the proposed revision to the MDL
procedure. Although EPA agrees with the theoretical arguments related
to the last suggestion regarding the spike level, EPA already tested
this suggestion in one of its studies of detection and quantitation
concepts and found that it could create laboratory burdens that far
exceed the benefits. Specifically, EPA required a spike-to-MDL ratio of
three in its multi-technique variability studies (the ``Episode 6000
studies''), which are described in the Assessment Document supporting
this rule. Two laboratories reported that a large number of iterations
would be required (particularly in multiple-analyte methods) in order
to achieved a spike-to-MDL ratio of three, and would result in
increased laboratory burden and cost. Therefore, this suggestion is not
incorporated into the revised MDL procedure in this proposed rule.
Based on peer review comments and comments received over the years
from the laboratory community, the Petitioners, and other stakeholders,
EPA is proposing revisions to the MDL procedure (see section VII
below).
VII. Proposed Revisions to the MDL and ML
This proposal would revise the definition of detection limit for
use under the CWA. It also would revise certain aspects of the existing
procedure for determining the Method Detection Limit (MDL) in 40 CFR
part 136, Appendix B (Definition and Procedure for the Determination of
the Method Detection Limit) and modify the discussion to clarify
implementation of the procedure. It also requests comment on whether to
add a stand-alone definition of quantitation limit and procedure for
determining the Minimum Level of Quantitation (ML) in Appendix B.
This proposal incorporates the results of EPA's recent assessment
of detection and quantitation concepts and procedures discussed
throughout this preamble and in the Assessment Document, and address
various stakeholder comments received by EPA since the 1984
promulgation of the MDL (49 FR 43234, October 26, 1984).
The following discussion is divided into five sections: (1)
Revisions to the definition of the detection limit are discussed in
section VII.A; (2) technical revisions to the MDL procedure are
discussed in section VII.B; (3) clarifications and other minor
editorial changes to the MDL procedure are discussed in section VII.C;
(4) the addition of a definition of quantitation limit and the addition
of a procedure to calculate the ML are discussed in section VII.D; (5)
section VII.E discusses EPA's continued acceptance of analytical
methods from organizations that do not necessarily use EPA's MDL and ML
procedures.
A. Definition of the Detection Limit
Section 136.2(f) currently defines the term ``detection limit'' to
mean ``the minimum concentration of an analyte (substance) that can be
measured and reported with a 99% confidence that the analyte
concentration is greater than zero as determined by the procedure set
forth at appendix B of this part.'' EPA is proposing to revise Sec.
136.2(f) to explicitly equate the term ``detection limit'' with the
``method detection limit'' and to reflect the proposed revisions to the
MDL procedure at Appendix B as follows: ``Detection limit means the
method detection limit (MDL), as determined by the procedure set forth
at Appendix B of this part. The MDL is an estimate of the measured
concentration at which there is 99% confidence that a given analyte is
present in a given sample matrix.'' EPA also is proposing to revise the
definition of the Method Detection Limit included in Appendix B as
follows: ``The MDL is an estimate of the measured concentration at
which there is 99% confidence that a given analyte is present in a
given sample matrix.'' The MDL is the concentration at which a decision
is made regarding whether an analyte is detected by a given analytical
method. The MDL is calculated from replicate analyses of a matrix
containing the analyte and is functionally analogous to the ``critical
value'' described by Currie (1968, 1995) and the Limit of Detection
described by the American Chemical Society (Keith et al., 1980,
McDougal et al., 1983).
EPA also is requesting comment on an alternative approach in which
the term limit of detection would be defined at Sec. 136.2 as ``the
critical value, which is the concentration at which there is 99%
confidence that a given analyte is present in a given sample matrix,''
and the method detection limit would be defined as ``the procedure set
forth in Appendix B of this part, which can be used to estimate the
limit of detection (i.e., critical value).''
B. Technical Revisions to the MDL Procedure
This notice proposes several technical revisions to the MDL
procedure at 40 CFR part 136, Appendix B. These revisions are based on
EPA's recent assessment of detection and quantitation concepts
described in the Assessment Document, as well as comments received from
stakeholders, the Petitioners, and the peer reviewers of the
assessment. Specifically, the proposed revisions would:
[[Page 11780]]
1. Revise the definition of the MDL to replace the term ``minimum
concentration'' with the term ``estimate of the measured
concentration'' and replace the phrase ``greater than zero'' with the
phrase ``present in a given sample matrix.'' The revised definition
would note the functional analogy of the MDL with the ``critical
value'' described by Currie (1968 and 1995) and the ``limit of
detection'' (LOD) described by the American Chemical Society in 1980
and 1983. The revised definition also would note that the MDL
represents the concentration at which the detection decision is made.
These proposed revisions are intended to make the definition of the MDL
more consistent with the MDL procedure. The proposed revisions reflect
peer review comments on EPA's recent assessment of detection and
quantitation concepts and procedures.
2. Expand the Scope and Application discussion to recognize that
there are a variety of purposes and analytical methods for which the
MDL procedure may be employed. The revised text provides examples of
four common uses of the MDL procedure (i.e., demonstrating laboratory
capability with a particular method; monitoring trends in laboratory
performance; characterizing method sensitivity in a particular matrix;
and establishing an MDL for a new or revised method for nationwide
use). The revised text also clarifies that the procedure may not be
applicable to certain test methods such as those used to measure pH or
temperature, for example. These revisions are based on questions from
stakeholders about the scope and applicability of the MDL procedure.
3. Revise three of the four considerations for estimating the
detection limit (see Step 1 of the current MDL procedure and section
4.3 of the proposed revisions), and suggest that the method-specified
MDL can be used as the initial estimate when performing an MDL study to
verify laboratory performance or to demonstrate that the MDL can be
achieved in a specific matrix. The proposed revisions to the original
considerations include: (1) Clarifying that, if analysis of blank
samples yields an instrument response, the detection limit can be
estimated as approximately equal to three times the standard deviation
of replicate measurements of the analyte in the blank; (2) replacing
``that region of the standard curve where there is a significant change
in sensitivity (i.e., a break in the slope of the standard curve)''
with ``a concentration in the region of constant or effectively-
constant standard deviation at low concentrations;'' and (3) replacing
``instrumental limitations'' with ``the lowest concentration that can
be detected by analyzing samples containing successively lower
concentrations of the analyte.''
4. Revise the specifications for establishing the test
concentration range according to the intended application of the MDL as
follows: (1) If verifying a published MDL, the test concentration
should be no more than five times the published MDL; (2) if verifying
an MDL to support a regulatory objective or the objective of a study or
program, the test concentration should be no more than one third the
compliance or target limit; (3) if determining an MDL for a new or
revised method, the test concentration should be no more than five
times the estimated detection limit; and (4) if performing an
iteration, the test concentration should be no more than five times the
MDL determined in the most recent iteration. (See Step 3.1 of the
current procedure and section 4.3.1 of the proposed revisions.)
5. Delete the calculation of a 95% confidence interval estimate for
the MDL. EPA has determined that these calculations are neither
routinely performed by laboratories, nor are the results employed by
regulatory agencies, including EPA.
6. Revise the discussion of the iterative procedure to require that
the iterative procedure be used to verify the reasonableness of the MDL
when developing an MDL for a new or revised method or when developing a
matrix-specific MDL, but that it remain optional when determining an
MDL to verify a method-, matrix-, program-, or study-specific MDL. This
change recognizes that the iterative procedure is rarely used to verify
laboratory performance, but is considered important during method
development. The discussion, as revised, also would provide specific
instructions on how to assess the reasonableness of an MDL used to
verify laboratory performance. (See Step 7 of the current procedure and
section 4.8 of the proposed revision.)
7. Add a new section (section 4.9) to the MDL procedure to address
the treatment of suspected outliers. EPA is proposing to add this
section in response to frequent questions from stakeholders with regard
to outliers in the absence of any affirmative statements in the current
MDL procedure. The discussion in this proposed section specifies that
suspected outliers be examined for spurious errors that may occur as a
result of human error or instrument malfunction, recommends that
correctable errors be corrected before calculation of the MDL, and
requires that any corrective actions be documented. The proposed
section specifically would provide for invalidation of results from
noncorrectable errors and preclude their use in calculating the MDL.
The proposed section also describes the use of the Grubbs test for
outlying values as a means to screen the results of the replicate
samples for possible outliers, and provides an example application of
the Grubbs test. Finally, the proposed section would reiterate the
requirement that any results generated from more than seven replicates
must be used to calculate the MDL unless they are determined to be
outliers by the use of an appropriate outlier test. This proposed
change addresses the possibility that some laboratories could prepare
more than the requisite seven samples and then select only the seven
results that yield the most desirable MDL value. Laboratory auditors
from various agencies have identified this practice as a problem that
can distort the MDL, but it is not specifically prohibited or addressed
in the current procedure.
8. Delete the discussion of analysis and use of blanks included in
section 4(a) of the current procedure. The current discussion applies
to methods in which a blank measurement is required to calculate the
measured level of an analyte; it requires separate measurements of
blank samples for each MDL sample aliquot analyzed and subtraction of
the average result of the blank samples from each respective MDL sample
measurement. The proposed deletion of this discussion is in recognition
that subtraction of a single (or average) blank sample result from the
result for each MDL sample would not change the standard deviation and
thus, would have no effect on the resulting MDL. Although EPA believes
laboratories would be prudent to analyze blanks for assessing potential
contamination, EPA also believes that requiring analysis of blanks or
subtraction of blank results during MDL determinations is unnecessarily
burdensome.
9. Revise the optional pre-test described in section 4(b) of the
current procedure. The current procedure suggests analyzing two
aliquots to evaluate the estimated detection limit before proceeding
with the full seven-replicate test. Results from these analyses are
evaluated to determine if the sample is in the ``desirable range for
determining the MDL,'' but no criteria are provided for establishing
this desirable range. The proposed revisions
[[Page 11781]]
to the pre-test procedure are intended to address this issue. These
revisions now appear in section 4.1 of the proposed procedure.
Specifically, the pre-test has been modified to suggest analysis of
three aliquots. Results from these analyses are evaluated by
calculating a preliminary MDL based on the standard deviation of the
analyses, and then determining if this preliminary MDL is within 0.2 to
1.0 times the concentration spiked in the sample. This revision is
consistent with the current procedure's recommendation that samples
used to determine an MDL contain the analyte at a concentration that is
``between 1 and 5 times the estimated method detection limit.''
C. Editorial Changes to the MDL Procedure
This notice proposes editorial changes to the MDL procedure at 40
CFR part 136, Appendix B that are designed to clarify the existing
procedure and improve readability. These editorial changes include
changes to the numbering scheme, the addition of clearer titles to some
of the procedural steps, and minor clarifications. Specifically, the
proposed changes would:
1. Add a summary section to provide an overview of the various
steps included in the MDL procedure. The summary section is consistent
with the current format for analytical methods and should be
particularly helpful to non-laboratory readers.
2. Clarify in the Scope and Application discussion that the MDL
procedure is intended for use in EPA's Clean Water Act programs, and
that alternative procedures may be used to establish test method
sensitivity provided the resulting detection value meets the
sensitivity needs for a specific application.
3. Clarify throughout the procedure that not all of the steps are
required for every application. This clarification provides consistency
with the proposed revisions in the Scope and Application section of the
procedure.
4. Expand the discussion of matrix selection to address use of an
MDL in either a reference matrix or an alternate matrix. (See Step 2 of
the current procedure and section 4.2 of the proposed revisions.) Use
of matrices other than reagent water are not discussed until Step 3b of
the current procedure. The expanded discussion is intended to provide
additional clarity and consistency with the description of the four
applications added to the MDL Scope and Application section (see
section VII.B.2 above).
5. Expand the discussion of establishing the test concentration
range to more clearly describe the steps required and prepare the test
samples. (See Step 3 of the current procedure and section 4.3 of the
proposed revisions.) These proposed changes are editorial and describe
the process that may be used for determining a matrix-specific MDL as
well as determining an MDL in a reference matrix such as reagent water.
Additional clarifications include recognition that some analytes may
require that seven aliquots be prepared individually, as opposed to
preparing a bulk sample of sufficient volume to be split into seven
aliquots. EPA is proposing this clarification in response to questions
from laboratories regarding the appropriate means for preparing the MDL
aliquots.
6. Expand the discussion of performing the analyses to include a
brief introduction clarifying that the samples used for MDL analyses
must be processed using the sample handling, processing, and result
calculations specified in the analytical method. (See Step 4 of the
current procedure and section 4.4 of the proposed revisions.) This
proposed change includes moving this statement from the Reporting
section of the current procedure to the more appropriate location in
section 4 of the revised procedure. This proposed change also would
clarify that blank-correction or recovery-correction procedures are
applied to the MDL analyses only when those procedures are employed for
routine sample analyses, and precludes their use if they are not
specified in the test method. EPA is proposing these changes in
response to questions raised by laboratories, the Petitioners, and as a
result of the recent assessment.
7. Reorganize the procedural steps contained in Step 4 of the
current procedure, such that the optional pre-test of the MDL is
discussed before the procedure for performing the full seven-replicate
test. (See section 4.4 of the proposed revisions.) EPA is proposing
this change strictly to improve ease of use.
8. Expand and reorganize the description of the seven-replicate
version of the MDL described in Step 4(a) of the current procedure. The
revised version would appear in section 4.5 and reflects comments from
stakeholders that the discussion in the current procedure is not
sufficiently clear. The revised procedure also would state explicitly
that all analytical results must be positive numbers, and that the
results from all aliquots analyzed must be used in the calculations,
except those identified as outliers using the procedures described in
section 4.9 of the revised procedure (see the discussion regarding
outliers in VII.B above). These proposed changes would clarify
stakeholder concerns regarding those analytical methods (e.g., for
metals) that may produce negative numbers at very low concentrations
and would emphasize the revision made in response to concerns regarding
inappropriate screening of results used for MDL determinations.
9. Simplify the calculations of standard deviation of replicate
measurements in Step 5 of the current procedure. (See section 4.6 of
the proposed revisions.) For example, the current procedure details the
calculation of the sample variance (s2), and then details
the calculation of the sample standard deviation (s) in a separate
equation. Given that the variance term does not factor into the MDL
calculation directly, the proposed revision would require only
calculation of the standard deviation. The proposed revision also would
include a caution warning the reader to calculate the sample standard
deviation (s), not the population standard deviation (sigma), when
using automated programs such as spreadsheets. This error was not as
likely to occur in 1984, prior to the ready availability of personal
computers and laboratory data systems, but is commonly seen today.
10. Move the table of Student's t-values from its current location
following the text in Step 7 to section 4.7, where the t-value is
employed. EPA is proposing this change to improve ease of use and
increase readability.
11. Add a table of F-statistic values to the iterative procedure
described in section 4.8. EPA is proposing this change to improve ease
of use and address those instances in which an iterative MDL might be
determined from other than seven replicates per data set.
12. Delete the ``Reporting'' section of the MDL procedure. The
existing procedure includes a section listing the information that must
be provided with the MDL for each analyte. EPA is proposing to delete
this section because it is not relevant to the procedure and it is
generally duplicative of reporting and recordkeeping requirements that
States, other regulatory entities, or laboratory certification
officials already require.
D. Definition and Procedure for Determining the Minimum Level of
Quantitation
Although ML values for analytes were published in 1984 in EPA
Methods 1624 and 1625 (49 FR 43234, October 26, 1984), the definition
of the ML was
[[Page 11782]]
provided in a footnote to the tables within those methods. The original
definition was intended to define a minimum level of quantitation for
these isotope dilution GC/MS methods. However, as described in the
Assessment Document, EPA has changed the definition of the ML over the
years and has expanded its applicability to other 40 CFR part 136
methods. This proposal requests comment on whether to add the following
definition of the ML to Appendix B of 40 CFR part 136: `` the lowest
level at which the entire analytical system gives a recognizable signal
and acceptable calibration point for the analyte, as determined by the
procedure set forth at Appendix B of this part. The ML represents the
lowest concentration at which an analyte can be measured with a known
level of confidence.'' In addition to the definition, EPA requests
comment on whether Appendix B should contain an explicit explanation of
the calculation of the ML from an MDL value determined using the
revised MDL procedure, including a table of multiplier values that may
be used when the MDL value is calculated from other than seven
replicate analyses.
An alternative is to not incorporate a definition in Sec. 136.2
but to continue to specify the ML on a method-by-method basis. In this
case, the ML may continue to be determined and supported with data
gathered during method validation studies. This approach would allow
maximum flexibility to design studies that are appropriate for the
intended use of the method.
A second alternative is to incorporate into Sec. 136.2 the
definition of limit of quantitation as ``The lowest concentration of an
analyte that can be measured with a defined level of confidence'' and
to incorporate the definition of ML (minimum level) as ``The procedure
set forth in Appendix B of this part of the same name, which can be
used to estimate the limit of quantitation.''
In this proposal, EPA is also requesting comment on whether it
should encourage or require that laboratories periodically demonstrate
target analyte recovery at the ML by preparing and analyzing a
reference matrix sample spiked at the ML using all sample handling and
processing steps described in the method. EPA recognizes that existing
methods do not provide acceptance criteria for such ``ML standards.''
Therefore, EPA suggests that, if the method does not provide acceptance
criteria for an ML standard, acceptance criteria for other spiked
reference matrix samples (e.g., laboratory control samples, laboratory
fortified blanks, ongoing precision and recovery samples, etc.) may be
used to evaluate analyte recovery at the ML. EPA is soliciting comment
on whether this recommendation should be made into a mandatory
requirement, retained as a recommendation, or replaced by an
alternative recommendation for demonstrating recovery at the ML.
E. Acceptance of Test Methods Employing Alternative Detection and
Quantitation Procedures
This proposed rule would allow use of alternative detection and
quantitation procedures to establish detection and quantitation limits
in an analytical method, provided that the resulting detection and
quantitation limits meet the sensitivity needs for the specific
application. The use of detection and quantitation approaches from
voluntary consensus standards bodies (VCSBs) and other organizations is
encouraged under the National Technology Transfer and Advancement Act
(NTTAA), because it facilitates the approval of analytical methods from
these organizations at 40 CFR part 136 without requiring that these
organizations specifically employ EPA's MDL and ML procedures to
establish method sensitivity. This allowance would result in greater
flexibility to establish or improve the sensitivity of methods for use
under the Clean Water Act. It also would facilitate approval of
analytical methods from VCSBs and other organizations. In selecting an
appropriate test method for a specific purpose, the laboratory must
always consider the sensitivity of the approved test methods. Only
those test methods with the desired sensitivity should be used to meet
the objective of the CWA ``to restore and maintain the chemical,
physical, and biological integrity of the Nation's waters.''
EPA recognizes that there are alternative detection and
quantitation approaches that may be used for determining test method
sensitivity. EPA has included test methods at 40 CFR part 136 that
employ alternative approaches, although some of these approaches have
not been rigorously defined. In its recent assessment of detection and
quantitation approaches, EPA evaluated the interlaboratory detection
estimate (IDE) and the interlaboratory quantitation estimate (IQE)
procedures published by ASTM International. However, EPA is not aware
at this time of any published test methods from any source that include
specific values for the IDE and the IQE, including test methods
published by ASTM International. EPA will consider test methods that
include these procedures for use in CWA programs when such methods are
available. If ASTM International is successful in developing single-
laboratory adaptations of the IDE and IQE that may be used to verify
the ability of a given laboratory to achieve the IDE and IQE, then EPA
also may consider those single-laboratory approaches in evaluating both
method and laboratory performance.
VIII. Industry Proposal
On December 27, 2002, the Inter-Industry Analytical Group (IIAG)
submitted a proposal that recommends (1) a sensitivity test intended to
``replace the MDL as a test of whether an individual laboratory is
performing adequately,'' and (2) an interlaboratory validation study
design intended to characterize precision and accuracy of methods used
for regulatory compliance. EPA did not have the opportunity to evaluate
IIAG's proposal against the criteria discussed in Section IV of this
preamble, but intends to do so prior to publication of a final rule.
EPA is providing a summary of the recommendations contained in the
``Inter-Industry Analytical Group Proposal for Sensitivity Test and
Full-Range Interlaboratory Validation Study'' here. The complete text
of the recommendations has been placed in the docket supporting this
proposed rule. EPA is soliciting comment on the industry
recommendations.
IIAG is proposing a sensitivity test in place of the MDL for
determining laboratory performance capability. The proposed sensitivity
test includes the provision that EPA first determine the lowest
calibration point of a method, prescribe a dilution of that calibration
point as the spike level (e.g., at one-half or two-thirds the lowest
calibration point), specify a required number of replicates, and set a
quality control acceptance criterion. IIAG asserts that an advantage of
such a test is that it would provide all laboratories with a single
spike level and an ``unambiguous pass or no-pass test.'' EPA is
soliciting comment on approaches that might be considered appropriate
for such determinations (i.e., the lowest calibration point of a
method, an appropriate dilution, a number of replicates, and an
acceptance criterion for standard deviation between measurements of the
replicates). EPA also is soliciting comment on how IIAG's recommended
sensitivity test would be either more appropriate or less appropriate
than either the current MDL and ML procedures or the MDL and ML
[[Page 11783]]
procedures if revised according to this proposed rule.
IIAG's proposed ``full range'' validation study is intended to
determine precision and bias across the entire working range of an
analytical method (i.e., from a blank to the upper end of the working
range) and would account for variability between laboratories. IIAG
recommends that, unlike the MDL and IIAG's proposed sensitivity test,
the ``full-range'' validation study could be used to characterize bias
and precision across the entire working range of the method and results
of such a study could be used to establish an interlaboratory method
detection level. EPA is requesting comment on the use of data generated
through a ``full range'' validation study to determine a quantitation
level, detection level, and corresponding bias and precision criteria
that are applicable throughout the entire working range of the method.
EPA also is soliciting comment on how IIAG's recommended ``full range''
validation study would be either more appropriate or less appropriate
than EPA's use of interlaboratory validation studies, which are
designed in accordance with ASTM Standard D 2777, or other appropriate
standards. For example, EPA used the ASTM standard to validate EPA
Method 1631 (see Interlaboratory Validation Study of EPA Method 1631).
IX. Solicitation of Comments
EPA is hereby requesting public comment on the proposed revisions
discussed in section VII of this preamble and on the industry proposal
discussed in section VIII. Specifically, EPA is requesting comment on
the proposed revisions to the Definition and Procedure for the
Determination of the Method Detection Limit at 40 CFR part 136
(Appendix B), to the proposed revision to the definition of ``Detection
Limit,'' on whether EPA should add definition of ``Minimum Level'' at
40 CFR 136.2, and on whether and how the sensitivity test described in
the industry proposal could be used in CWA programs. EPA is also
requesting public comment on the Assessment Document supporting the
proposed revisions discussed in this notice elsewhere in today's
Federal Register (see Notice of Document Availability and Public
Comment Period for the Technical Support Document for the Assessment of
Detection and Quantitation Concepts).
Commenters are encouraged to support their views with data or
information that would assist EPA in making a final decision on
detection and quantitation procedures for EPA's CWA applications. To
ensure that EPA can properly respond to comments, commenters should
cite, where possible, the paragraph(s) or section(s) in this proposal
to which each comment refers. For further details on submission of
comments, please see the DATES; ADDRESSES; and ``How to Submit
Comments'' sections at the beginning of this preamble.
EPA is particularly requesting comment on the following:
1. EPA is requesting comment on whether to include a definition and
procedure for the ML in Appendix B of 40 CFR part 136 (see section
VII.D of this preamble). EPA is soliciting comment on whether the
proposed addition of an ML definition and procedure in Appendix B is
appropriate, or whether either of the alternatives discussed in section
VII.D are more appropriate to maintain flexibility in the application
of different quantitation approaches.
2. EPA is proposing a recommendation that laboratories periodically
demonstrate target analyte recovery at the ML by preparing and
analyzing a reference matrix sample spiked at the ML (see section VII.D
of this preamble). Specifically, EPA is soliciting comment on whether
this recommendation should be made into a mandatory requirement,
retained as a recommendation, or replaced by an alternative
recommendation for demonstrating recovery at the ML. EPA also is
soliciting comments and recommendations regarding procedures for
establishing acceptance criteria for ML recovery, and when application
of the criteria would be appropriate (e.g., development of new methods,
validation of data), if such a requirement were mandatory.
3. EPA is proposing to add a new Step 8 to the MDL procedure to
address the identification and treatment of suspected outliers (see
Section VII.B.7 of this preamble). This proposed step includes
provision for invalidation of results from noncorrectable errors and
precludes their use in calculating the MDL. The proposed step also
states: ``Given the small number of replicates typically used to
determine the MDL, it is inappropriate to use a data set that contains
more than one statistical outlier.'' EPA requests comment on (1) the
procedures for identifying outliers, (2) the specification that only
one outlier may be removed from a data set that is used for MDL
determination, and (3) the appropriateness of allowing use of a data
set containing six results if an outlier is identified and removed from
a data set containing results from the required minimum of seven
replicate samples.
4. EPA is proposing to revise the specifications for establishing
the test concentration (spike level) that will be used in the
determining the MDL according to the intended application of the MDL
(see Section VII.A.4 of this preamble). EPA is soliciting comment on
these levels and on the appropriateness of applying these levels
according to the intended use of the MDL.
5. EPA is soliciting comment on the sensitivity test and ``full-
range'' validation study described by IIAG and included in the public
docket supporting this proposed rule (see Section VII of this
preamble). EPA is specifically soliciting comment on those aspects of
IIAG's proposed study that relate to detection and quantitation issues.
6. EPA is proposing to delete the Reporting section of the existing
MDL procedure. EPA is soliciting comments on whether this change is
appropriate.
X. Statutory and Executive Order Reviews
A. Executive Order 12866: Regulatory Planning and Review
Under Executive Order 12866 (58 FR 51735 (October 4, 1993)), the
Agency must determine whether the regulatory action is ``significant''
and therefore subject to Office of Management and Budget (OMB) review
and the requirements of the Executive Order. The Executive Order
defines ``significant regulatory action'' as one that is likely to
result in a rule that may:
(1) Have an annual effect on the economy of $100 million or more,
or adversely affect in a material way the economy, a sector of the
economy, productivity, competition, jobs, the environment, public
health or safety, or State, local, or Tribal governments or
communities;
(2) Create a serious inconsistency or otherwise interfere with an
action taken or planned by another agency;
(3) Materially alter the budgetary impact of entitlements, grants,
user fees, or loan programs or the rights and obligations of recipients
thereof; or
(4) Raise novel legal or policy issues arising out of legal
mandates, the President's priorities, or the principles set forth in
the Executive Order.
It has been determined that this rule is not a ``significant
regulatory action'' under the terms of Executive Order 12866 and is
therefore not subject to OMB review.
[[Page 11784]]
B. Paperwork Reduction Act
This action does not impose an information collection burden under
the provisions of the Paperwork Reduction Act, 44 U.S.C. 3501 et seq.
This action imposes no information collection, reporting or
recordkeeping requirements. Burden means the total time, effort, or
financial resources expended by persons to generate, maintain, retain,
or disclose or provide information to or for a Federal agency. This
includes the time needed to review instructions; develop, acquire,
install, and utilize technology and systems for the purposes of
collecting, validating, and verifying information, processing and
maintaining information, and disclosing and providing information;
adjust the existing ways to comply with any previously applicable
instructions and requirements; train personnel to be able to respond to
a collection of information; search data sources; complete and review
the collection of information; and transmit or otherwise disclose the
information.
An Agency may not conduct or sponsor, and a person is not required
to respond to a collection of information, unless it displays a
currently valid OMB control number. The OMB control numbers for EPA's
regulations are listed in 40 CFR part 9 and 48 CFR chapter 15.
C. Regulatory Flexibility Act
The Regulatory Flexibility Act (RFA) generally requires an agency
to prepare a regulatory flexibility analysis of any rule subject to
notice and comment rulemaking requirements under the Administrative
Procedure Act or any other statute unless the agency certifies that the
rule will not have a significant economic impact on a substantial
number of small entities. Small entities include small businesses,
small organizations, and small governmental jurisdictions.
For purposes of assessing the impacts of this rule on small
entities, small entity is defined as: (1) A small business as defined
by the U.S. Small Business Administration definitions at 13 CFR
121.201; (2) a small governmental jurisdiction that is a government of
a city, county, town, school district or special district with a
population of less than 50,000; and (3) a small organization that is
any not-for-profit enterprise which is independently owned and operated
and is not dominant in its field.
After considering the economic impacts of this proposed rule on
small entities, I certify that this action will not have a significant
economic impact on a substantial number of small entities. This rule
proposes to modify existing procedures in 40 CFR part 136, appendix B
for determination of detection and quantitation in analytical methods.
This modification would clarify and improve existing procedures.
Overall, the costs of this modification are minimal. Many
laboratories using analytical test methods are already implementing
aspects of the modification, further minimizing any potential cost
increases. Therefore, EPA believes that this rule will not have a
significant economic impact on a substantial number of small entities.
We continue to be interested in the potential impacts of the proposed
rule on small entities and welcome comments on issues related to such
impacts.
D. Unfunded Mandates Reform Act
Title II of the Unfunded Mandates Reform Act of 1995 (UMRA), Public
Law 104-4, establishes requirements for Federal agencies to assess the
effects of their regulatory actions on State, Tribal, and local
governments and the private sector. Under section 202 of the UMRA, EPA
generally must prepare a written statement, including a cost-benefit
analysis, for proposed and final rules with ``Federal mandates'' that
may result in expenditures to State, Tribal, and local governments, in
the aggregate, or to the private sector, of $100 million or more in any
one year. Before promulgating an EPA rule for which a written statement
is needed, section 205 of the UMRA generally requires EPA to identify
and consider a reasonable number of regulatory alternatives and adopt
the least costly, most cost-effective or least burdensome alternative
that achieves the objectives of the rule. The provisions of section 205
do not apply when they are inconsistent with applicable law. Moreover,
section 205 allows EPA to adopt an alternative other than the least
costly, most cost-effective or least burdensome alternative if the
Administrator publishes with the final rule an explanation of why that
alternative was not adopted.
Before EPA establishes any regulatory requirements that may
significantly or uniquely affect small governments, including Tribal
governments, it must have developed under section 203 of the UMRA a
small government agency plan. The plan must provide for the
notification of potentially affected small governments, enabling
officials of affected small governments to have meaningful and timely
input in the development of EPA regulatory proposals with significant
Federal intergovernmental mandates, and informing, educating, and
advising small governments on compliance with the regulatory
requirements.
This proposed rule contains no Federal mandate (under the
regulatory provisions of Title II of the UMRA) for State, Tribal, and
local governments or the private sector in any one year. This rule
imposes no enforceable duty on any State, local, or Tribal governments
or the private sector. This rule proposes to modify existing procedures
in 40 CFR part 136, appendix B for determination of detection and
quantitation in analytical methods. This modification would clarify and
improve current procedures. Overall, the costs of this modification are
minimal. Thus, this rule is not subject to sections 202 and 205 of the
UMRA. For the same reasons, EPA has also determined that this rule
contains no regulatory requirements that might significantly or
uniquely affect small governments. Thus, this rule also is not subject
to the requirements of section 203 of the UMRA.
E. Executive Order 13132: Federalism
Executive Order 13132, entitled ``Federalism'' (64 FR 43255, August
10, 1999), requires EPA to develop an accountable process to ensure
``meaningful and timely input by State and local officials in the
development of regulatory policies that have federalism implications.''
``Policies that have federalism implications'' is defined in the
Executive Order to include regulations that have ``substantial direct
effects on the States, on the relationship between the national
government and the States, or on the distribution of power and
responsibilities among the various levels of government.''
This proposed rule does not have federalism implications. It will
not have substantial direct effects on the States, on the relationship
between the national government and the States, or on the distribution
of power and responsibilities among the various levels of government,
as specified in Executive Order 13132. This rule proposes to modify
existing procedures in 40 CFR part 136, Appendix B for determination of
detection and quantitation in analytical methods. This modification
would clarify and improve existing procedures. The costs of this rule
for State and local governments are minimal. Thus, Executive Order
13132 does not apply to this rule. In the spirit of Executive Order
13132, and consistent with EPA policy to promote communications between
EPA and State and local governments, EPA specifically solicits comments
on this proposed rule from State and local officials.
[[Page 11785]]
F. Executive Order 13175: Consultation and Coordination with Indian
Tribal Governments
Executive Order 13175, titled ``Consultation and Coordination With
Indian Tribal Governments'' (65 FR 67249, November 9, 2000), requires
EPA to develop an accountable process to ensure ``meaningful and timely
input by Tribal officials in the development of regulatory policies
that have Tribal implications.'' ``Policies that have Tribal
implications'' is defined in the Executive Order to include regulations
that have ``substantial direct effects on one or more Indian Tribes, on
the relationship between the Federal government and the Indian Tribes,
or on the distribution of power and responsibilities between the
Federal government and Indian Tribes.''
This proposed rule does not have Tribal implications. It will not
have substantial direct effects on Tribal governments, on the
relationship between the Federal government and Indian Tribes, or on
the distribution of power and responsibilities between the Federal
government and Indian Tribes, as specified in Executive Order 13175.
This rule proposes to modify existing procedures in 40 CFR part 136,
Appendix B for determination of detection and quantitation in
analytical methods. This modification would clarify and improve
existing procedures. The costs of this rule for Tribal governments are
minimal. Thus, Executive Order 13175 does not apply to this rule. In
the spirit of Executive Order 13175, and consistent with EPA policy to
promote communications between EPA and Tribal governments, EPA
specifically solicits comments on this proposed rule from Tribal
officials.
G. Executive Order 13045: Protection of Children From Environmental
Health & Safety Risks
Executive Order 13045 (62 FR 19885, April 23, 1997) applies to any
rule that: (1) Is determined to be ``economically significant'' as
defined under Executive Order 12866, and (2) concerns an environmental
health or safety risk that EPA has reason to believe may have a
disproportionate effect on children. If the regulatory action meets
both criteria, the Agency must evaluate the environmental health or
safety effects of the planned rule on children, and explain why the
planned regulation is preferable to other potentially effective and
reasonably feasible alternatives considered by the Agency. This
proposed rule is not subject to Executive Order 13045 because it is not
``economically significant'' as defined in Executive Order 12866.
Furthermore, it does not concern an environmental health or safety risk
that EPA has reason to believe may have a disproportionate effect on
children.
H. Executive Order 13211: Actions That Significantly Affect Energy
Supply, Distribution, or Use
This rule is not subject to Executive Order 13211, ``Actions
Concerning Regulations That Significantly Affect Energy Supply,
Distribution, or Use'' (66 FR 28355 (May 22, 2001)) because it is not a
significant regulatory action under Executive Order 12866.
I. National Technology Transfer and Advancement Act
Section 12(d) of the National Technology Transfer and Advancement
Act of 1995, (``NTTAA''), Public Law 104-113, section 12(d) (15 U.S.C.
272 note), directs EPA to use voluntary consensus standards in its
regulatory activities unless to do so would be inconsistent with
applicable law or otherwise impractical. Voluntary consensus standards
are technical standards (e.g., material specifications, test methods,
sampling procedures, business practices) that are developed or adopted
by voluntary consensus standard bodies. The NTTAA directs EPA to
provide Congress, through the Office of Management and Budget (OMB),
explanations when the Agency decides not to use available and
applicable voluntary consensus standards.
This proposed rulemaking involves technical standards. Therefore,
the Agency identified and evaluated potential voluntary consensus
standards. Specifically, EPA identified and evaluated potential
detection and quantitation concepts and procedures published by the
American Society for Testing and Materials (ASTM International), from
the International Organization for Standardization (ISO), the
International Union of Pure and Applied Chemistry (IUPAC), and the
American Chemical Society (ACS). EPA determined that, although ISO,
IUPAC, and ACS have published terms and definitions for detection and
quantitation, these organizations have not published an applicable
standard (i.e., a step-by-step protocol to make a detection or
quantitation determination). EPA did identify applicable standards from
ASTM International (the IDE and IQE). This proposed rulemaking would
allow the use of these procedures for methods development purposes and
would allow the use of any analytical methods with an IDE and IQE,
provided these test methods meet the analytical sensitivity
requirements for a specific data use. There is currently no applicable
voluntary consensus standard for detection and quantitation for
laboratory quality control purposes. EPA welcomes comments on this
aspect of the proposed rulemaking and, specifically, invites the public
to identify potentially applicable voluntary consensus standards and to
explain why such standards should be used in this regulation.
XI. References
American Chemical Society, 1980: Analytical Chemistry 1980, 52,
2242-2249.
American Chemical Society, 1983: Analytical Chemistry 1983, 55,
2210-2218.
Budde, William L., Environmental Science and Technology 1981 15,
1426-1435.
Currie, 1968: Currie, Lloyd A. Anal. Chem. 1968 40, 586-593.
Currie, 1999: Currie, Lloyd A. Anal. Chim. Acta 1999 391, 127-
134.
Gibbons, 1997: Gibbons, Robert D.; Coleman, David E.; Maddalone,
Raymond F. Env. Sci. Technol. 1997, 31, 2071-2077).
Glaser, 1981: Glaser, John A., Foerst, Denis L., McKee, Gerald
D., Quave, Stephan A., and Budde, William L. (1981), Environ. Sci.
Technol., 15:1426.
Kahn, 1998: Kahn, Henry D.; Telliard, William A.; White, Charles
E. Env. Sci. Technol. 1998 32, 2346-2348.
Kahn, 1998: Kahn, Henry D.; Telliard, William A.; White, Charles
E. Env. Sci. Technol. 1999 33, 1315.
Maddalone, 1993: Maddalone, Raymond F.; Rice, James K.;
Edmondson, Ben C.; Nott, Babu R.; Scott, Judith W. Water Environment
and Technology 1993, 5, 1-4.
Rocke and Lorenzato, 1995: Rocke, D. M. and Lorenzato, S.
Technometrics 1995, 37, 176-184.
Appendix A: Definitions, Acronyms, and Abbreviations Used in This
Document
AAMA--American Automobile Manufacturers Association
ACS--American Chemical Society
AOAC--Association of Official Analytical Chemists (now AOAC-
International)
APHA--American Public Health Association
ASTM--American Society for Testing and Materials (now ASTM
International)
ATP--Alternate Test Procedure
AWWA--American Water Works Association
CBI--confidential business information
CFR--Code of Federal Regulations
CRV--critical value
CWA--Clean Water Act--Federal Water Pollution Control Act Amendments
(33 U.S.C. 1251 et seq.)
EPA--Environmental Protection Agency
EPRI--Electric Power Research Institute
FR--Federal Register
[[Page 11786]]
IDE--interlaboratory detection estimate
IIAG--Inter-Industry Analytical Group
IQE--interlaboratory quantitation estimate
ISO--International Organization for Standardization
IUPAC--International Union of Pure and Applied Chemistry
LOD--limit of detection
LOQ--limit of quantitation
MDL--method detection limit
MDV--minimum detectable value
ML--minimum level of quantitation
NBS--National Bureau of Standards (now NIST)
NIST--National Institute of Standards and Technology (formerly NBS)
NPDES--National pollutant discharge elimination system
NTTAA--National Technology Transfer and Advancement Act
OMB--Office of Management and Budget
POTW--Publicly-owned treatment works
RFA--Regulatory Flexibility Act
SBREFA--Small Business Regulatory Enforcement Fairness Act
SCC--Sample Control Center
TSD--technical support document
UMRA--Unfunded Mandates Reform Act
USATHAMA--U.S. Army Toxic and Hazardous Materials Agency (now the U.S.
Army Environmental Center [USAEC])
U.S.C.--United States Code
WQBEL--water-quality-based effluent limit
WEF--Water Environment Federation
List of Subjects at 40 CFR Part 136
Environmental protection, Reporting and recordkeeping requirements,
Water pollution control.
Dated: February 28, 2003.
Christine Todd Whitman,
Administrator.
For the reasons set out in the preamble, title 40, chapter I of the
Code of Federal Regulations, is proposed to be amended as follows:
PART 136--GUIDELINES ESTABLISHING TEST PROCEDURES FOR THE ANALYSIS
OF POLLUTANTS
1. The authority citation for part 136 continues to read as
follows:
Authority: Secs. 301, 304(h), 307, and 501(a), Pub. L. 95-217,
91 Stat. 1566, et seq. (33 U.S.C. 1251, et seq.) (The Federal Water
Pollution Control Act Amendments of 1972 as amended by the Clean
Water Act of 1977).
2. Section 136.2 is amended by revising paragraph (f) and adding
paragraph (g) to read as follows:
Sec. 136.2 Definitions.
* * * * *
(f) Detection limit means the method detection limit (MDL), as
determined by the procedure set forth at Appendix B of this part. The
MDL is an estimate of the measured concentration at which there is 99%
confidence that a given analyte is present in a given sample matrix.
(g) Minimum level of quantitation (ML) means the lowest level at
which the entire analytical system gives a recognizable signal and
acceptable calibration point for the analyte, as determined by the
procedure set forth at Appendix B of this part. The ML represents the
lowest concentration at which an analyte can be measured with a known
level of confidence.
3. Appendix B of part 136 is revised to read as follows:
Appendix B to Part 136
A. Definition and Procedure for the Determination of the Method
Detection Limit--Revision 2
1.0 Definition
The method detection limit (MDL) is an estimate of the measured
concentration at which there is 99% confidence that a given analyte
is present in a given sample matrix. The MDL is the concentration at
which a decision is made regarding whether an analyte is detected by
a given analytical method. The MDL is calculated from replicate
analyses of a matrix containing the analyte and is functionally
analogous to the ``critical value'' described by Currie (1968, 1995)
and the Limit of Detection (LOD) described by the American Chemical
Society (Keith et al., 1980, McDougal et al., 1983).
2.0 Scope and Application
2.1 This procedure is for the determination of an MDL for a
given analyte (parameter) in a given matrix (the component or
substrate that contains the analyte) using a given test procedure
(analytical method). It is applicable to a wide variety of analytes,
matrices, and instruments, and to a broad variety of physical and
chemical analytical methods, with some exceptions (e.g., pH,
temperature). This procedure is intended for use in EPA's Clean
Water Act (CWA) programs. An alternative procedure may be used
(e.g., from a voluntary consensus standards body) to establish the
sensitivity of an analytical method, provided the resulting
detection limit meets the sensitivity needs for the specific
application.
2.2 This procedure requires a complete, specific, and well-
defined analytical method. It is essential that all sample
processing steps of the analytical method that are applied to
routine analyses be included in determination of an MDL.
2.3 This procedure may be used for a variety of applications,
including, but not limited to:
2.3.1 Demonstrating laboratory capability with a particular
method. A laboratory using this procedure to demonstrate capability
with a particular method is not required to perform the iterative
verification of the MDL (section 4.8) if the laboratory-determined
MDL is less than or equal to either the MDL in the method, the MDL
required to support a regulation, or the objectives of a study (see
section 4.8.5).
2.3.2 Monitoring trends in laboratory performance. When used in
this manner, the MDL for a given analyte measured using a given
analytical method may vary as a function of laboratory experience
and the matrix tested.
2.3.3 Characterizing method sensitivity in a particular matrix.
An MDL is typically determined in a reference matrix. However, it
also may be determined in a real-world matrix to verify that the
target MDL can be achieved in that matrix.
2.3.3.1 If the MDL required for a specific application can be
achieved in a real-world matrix, that MDL may be used in lieu of a
reference-matrix MDL, and iteration (section 4.8) is not necessary.
2.3.3.2 If the MDL needed for a specific application cannot be
achieved in the real-world matrix (i.e., if the purpose of the MDL
study is to demonstrate the effects of matrix interferences in a
real world sample), the laboratory must (1) perform an MDL study in
a reference matrix to demonstrate the laboratory's ability to apply
the method in the absence of interferences, and (2) verify the
matrix-specific MDL through the iterative procedure given in section
4.8.
2.3.3.3 Refer to section 4.2 for additional information
concerning the selection of test matrices.
2.3.4 Establishing an MDL for a new or revised method for
nationwide use. When the procedure is used to establish an MDL for a
new or revised method, the MDL should be derived from data obtained
from multiple laboratories. Organizations developing or revising
methods must document and make available the data and procedures
used to establish an MDL to obtain approval for use under Clean
Water Act programs.
3.0 Summary of the Procedure
3.1 The procedural steps required for determining an MDL vary
with the intended application of the MDL. However, regardless of the
intended application, all MDL determinations must include the
following steps:
(a) Estimating the detection limit of the method as practiced,
(b) Selecting the appropriate matrix to be used in the
determination,
(c) Selecting the appropriate test concentration,
(d) Preparing and analyzing a minimum of seven replicate
aliquots of a blank or spiked matrix,
(e) Calculating the mean concentration of the analyte, the
standard deviation of that mean, and the MDL, using the formula
provided in this procedure,
(f) Comparing the calculated MDL to a method-specified MDL,
relevant regulatory requirements, or project-specific objectives, as
appropriate.
3.2 When developing MDLs for new or revised methods, or
developing matrix-specific MDLs for nationwide use, the procedure
also may include:
(a) Conducting an optional pre-test using fewer replicates to
verify that an appropriate
[[Page 11787]]
concentration was selected to perform the MDL test,
(b) Conducting an iterative procedure involving analyses of
additional replicates to verify the reasonableness of the MDL
(required for method development),
(c) Determining the MDL in additional relevant matrices or in
multiple laboratories.
4.0 Procedure
4.1 Estimate the detection limit of the method
If the purpose of determining the MDL is to verify laboratory
performance using a specific method or to determine the MDL in a
specific matrix, the laboratory should use the MDL published in the
method as the initial estimate. If the MDL is being determined for
other reasons (e.g., method development), the experience of the
laboratory is important to properly estimate the detection limit.
The laboratory must include at least one of the following
considerations in producing this initial estimate:
4.1.1 The concentration of analyte that produces an instrument
signal/noise in the range of 2.5 to 5 for those instances in which
an instrument is used for the determination.
4.1.2 The concentration approximately equal to three times the
standard deviation of replicate measurements of the analyte in a
blank. If analysis of the blank produces no response (zero), use the
concentration approximately equal to three times the standard
deviation of replicate measurements at the lowest concentration that
always produces a response.
4.1.3 A concentration in the region of constant or effectively
constant standard deviation at low concentrations. This assumes that
the model of Glaser et al. (1981), which includes a low
concentration region where the standard deviation of the measurement
error is constant or effectively constant, is suitable to describe
the measurement process for the analytical method under
consideration.
4.1.4 The lowest concentration that can be detected by analyzing
samples containing successively lower concentrations of the analyte.
4.2 Select the matrix to be used to develop the MDL. The MDL is
typically determined in a reference matrix. However, it may be
determined in a real-world matrix to verify that the MDL required
for a specific application can be achieved in that matrix.
4.2.1 Reference Matrix
The most common reference matrix is reagent water. Reagent water
is defined as water in which the analyte and interferences are not
detected at the MDL or, if this is the initial estimate, detected at
the detection limit estimated in section 4.1. An interference is
defined as a systematic error in the measured analytical signal
caused by the presence of a substance other than the analyte. Other
common reference matrices are sand as a reference matrix for soils,
sediments, and other solid samples; and corn oil as a reference
matrix for tissue samples. After selecting the reference matrix to
be tested, proceed to section 4.3.
4.2.2 Matrices other than a reference matrix
4.2.2.1 If the MDL determined in a matrix other than a reference
matrix is sufficient to meet requirements of the specific
application (e.g., the laboratory is able to meet the MDL required
for compliance monitoring or published in the method), it is not
necessary to determine the MDL in a reference matrix.
4.2.2.2 If the purpose of a matrix-specific MDL is to determine
the effects of matrix interferences in a real-world sample, the
laboratory also must determine the MDL in a reference matrix to
demonstrate the laboratory's ability to apply the method in the
absence of interferences.
Note to Section 4.2.2.2: A laboratory seeking to develop a
matrix-specific MDL for a specific method must use the same cleanup
steps that will be used for analysis of samples.
4.3 Establish the test concentration range and prepare test
samples Establish the test concentration range per section 4.3.1.
Prepare the test samples from a reference matrix per section 4.3.2,
or from an alternative matrix per section 4.3.3. Prepare a
sufficient quantity of the matrix to provide samples for a minimum
of seven analyses.
Note to Section 4.3: For analytes for which a single-volume
(bulk) sample or spiked single-volume sample would result in non-
homogenous replicates (e.g., for determination of ``oil and
grease''), or for which preparation of a spiked single-volume sample
is impractical, a minimum of seven individual aliquots should be
prepared at the test concentration.
4.3.1 Establish the test concentration range as follows.
4.3.1.1 If verifying an MDL that is published in an analytical
method, the test concentration should be no more than five times the
published MDL.
4.3.1.2 If verifying an MDL required to support a regulatory
objective or the objective of a specific study or program, the test
concentration should be no more than one third the compliance or
target limit.
4.3.1.3 If performing an MDL study for a new or revised method,
the test concentration should be no more than five times the
detection limit estimated in section 4.1.
4.3.1.4 If performing an iteration (see section 4.8), the test
concentration should be no more than five times the MDL determined
in the most recent iteration.
4.3.2 Preparing test samples from a reference matrix
If a blank sample produces an acceptable signal (see section
4.3.2), spiking is not required; otherwise, spike the reference
matrix at the concentration established in section 4.3.1. Proceed to
section 4.4.
Note to Section 4.3.2: The laboratory must ensure that the
levels in blanks are not too high. Otherwise, the resulting MDL
produced may be artificially biased. For a spiked sample, the
concentration of the contaminant in the blank should not be a
significant portion of the total concentration since this also could
result in an artificial bias for the MDL. It is important to spike
the analyte at the proper concentration (section 4.3) to ensure the
MDL is determined accurately.
4.3.3 Preparing test samples from a matrix other than a
reference matrix
Analyze three aliquots of the sample matrix to characterize the
concentration of the target analyte(s) present in the matrix.
4.3.3.1 If the average measured concentration of the analyte in
the matrix is less than five times the concentration established in
section 4.3.1, proceed to section 4.4.
4.3.3.2 If the average measured concentration of the analyte in
the matrix is less than the concentration range established in
section 4.3.1, spike the matrix to bring the concentration of the
analyte to the established concentration range and proceed to
section 4.4.
4.3.3.3 If the average measured concentration of the analyte in
the matrix is greater than the concentration range established in
section 4.3.1, reduce the concentration of the analyte to the
established concentration range, using one of the following
techniques before proceeding to section 4.4:
4.3.3.3.1 Selectively remove the analyte from the matrix.
4.3.3.3.2 Obtain another matrix with a lower concentration of
the analyte.
4.3.3.3.3 Dilute a sample of the matrix with the appropriate
reference matrix. For example, if the matrix is aqueous, dilute the
sample with reagent water.
Note to Section 4.3.3.3.3: Dilution should be used only if the
analyte cannot be selectively removed (3.3.3.1) or if another matrix
with a lower analyte concentration cannot be obtained (3.3.3.2)
because dilution of the sample has the potential to dilute any
interferences present.
4.4 Perform the analyses
4.4.1 The analyses in section 4.4.3 (optional pre-test of
estimated detection limit) and 4.2 (MDL analyses) must be performed
using all of the routinely employed calibration, sample handling,
processing, and result calculations specified in the analytical
method. For example, many methods contain multiple sample cleanup
options; any and all cleanup options routinely used to analyze a
sample must be used when analyzing the replicate samples prepared in
section 4.3.
4.4.2 Similarly, if the analytical method employs recovery-
correction or blank-correction procedures for calculating results,
those procedures must be used when calculating results of an
analysis of each aliquot. If a recovery- or blank-correction
procedure is not specified in the test method, such correction must
not be used.
4.4.3 Optional pre-test
It may be economically and technically desirable to evaluate the
estimate of the detection limit (section 4.1) before proceeding with
determination of the MDL in section 4.5. This pre-test attempts to
ensure that the MDL study is being conducted at the correct
concentration to prevent repeating the entire study; it may be
particularly useful when the analytical costs are high. To evaluate
the estimated detection limit, proceed as follows:
4.4.3.1 Process three aliquots of the test sample prepared in
section 4.3 through the entire method, per section 4.5.
4.4.3.2 Calculate the standard deviation of results for the
three aliquots as follows:
[[Page 11788]]
[GRAPHIC] [TIFF OMITTED] TP12MR03.047
Where:
Xi = a result in the method reporting units obtained from
analysis of a sample aliquot, i=1 to 3
X = mean of the three results, and
n = number of sample aliquots (3 in this case)
4.4.3.3 Calculate a preliminary MDL as follows:
Preliminary MDL = 6.96s
Where:
6.96 = Student's t-value appropriate for a 99% confidence level and
two degrees of freedom
s = standard deviation of the results of analyses of the three
replicates from section 4.4.3.2
4.4.3.4 If the preliminary MDL is in the range of 0.2--1.0 times
the concentration in the spiked sample (section 4.3), analyze a
minimum of four additional aliquots and proceed using the procedure
in section 4.5. Use all seven measurements for calculation of the
MDL. Otherwise, produce a new bulk sample per section 4.3, with the
analyte at the concentration of the preliminary MDL and either
repeat section 4.4.3, or proceed to section 4.5 for determination of
the MDL.
4.5 MDL determination
4.5.1 Process at least seven aliquots of the test sample
prepared in section 4.4 or section 4.4.3 through the entire
analytical method.
4.5.2 Make all computations as specified in the method, with
final results in the method-specified reporting units.
4.5.3 To obtain a valid MDL, all of the analytical results must
be positive numbers. If any of the results are negative or zero,
increase the test concentration (per section 4.3) and repeat the MDL
procedure.
4.5.4 If more than seven aliquots are prepared and analyzed, the
results from all the aliquots must be used to calculate the MDL,
except as described in section 4.9.
4.6 Calculate the standard deviation, s, as follows:
[GRAPHIC] [TIFF OMITTED] TP12MR03.048
Where:
Xi = a result, in the method reporting units, obtained
from analysis of a sample aliquot, i=1 to n
X = mean of the results, and
n = number of sample aliquots
Note to Section 4.6: When using a program such as a spreadsheet
to calculate the standard deviation (s), make certain that the
sample standard deviation, which uses (n-1) in the denominator, is
calculated, rather than the population standard deviation ([sigma]),
which uses n in the denominator.
4.7 Calculate the MDL
[GRAPHIC] [TIFF OMITTED] TP12MR03.049
Where:
s = standard deviation of the results calculated in section 4.6
t(n-1, 1-[alpha]=0.99) = Students'
t-value appropriate for a 99% confidence level and (n-1)
degrees of freedom, from the table below.
Table of Student's t-Values at the 99% Confidence Level
------------------------------------------------------------------------
Number of replicates for
--------------------------------------------- Degrees of
Iterative freedom t(n-1, 1-
Singles MDL (df = n-1) MDL (df = (df) [alpha]=0.99)
n-2)
------------------------------------------------------------------------
7.............................. N/A 6 3.143
8.............................. N/A 7 2.998
9.............................. N/A 8 2.896
10............................. N/A 9 2.821
11............................. N/A 10 2.764
12............................. N/A 11 2.718
13............................. 14 12 2.681
14............................. 15 13 2.650
15............................. 16 14 2.624
16............................. 17 15 2.602
17............................. 18 16 2.583
18............................. 19 17 2.567
19............................. 20 18 2.552
------------------------------------------------------------------------
Note to Section 4.7: Degrees of freedom = (n-1) if a single MDL
study is performed. If an iterative MDL study is performed, degrees
of freedom = (nh + n1-2), as described in
section 4.8; N/A indicates that the number of degrees of freedom in
this row does not apply to an iterative MDL study.
4.8 Iterate and verify the reasonableness of the MDL
When developing an MDL for a new or revised method, or when
developing a matrix-specific MDL, the MDL procedure must be iterated
and the reasonableness of the MDL determined using an F-test, as
described in sections 4.8.1 through 4.8.4. When verifying a method-,
matrix-, program-, or study-specific MDL, the MDL is determined as
described in section 4.8.5 and iteration may not be necessary.
4.8.1 Iteration
When developing an MDL for a new or revised method, the spiking,
analysis, and calculation steps (sections 4.3 to 4.6) must be
repeated using a spike at no more than five times the MDL determined
initially or in the most recent iteration, to confirm the
reasonableness of the MDL.
4.8.2 Once the iteration is complete (i.e., two successive MDL
estimates have been produced), calculate the F-ratio (F) as:
[GRAPHIC] [TIFF OMITTED] TP12MR03.050
Where:
sh\2\ = variance estimate from the higher spike
concentration
sl\2\ = variance estimate from the lower spike
concentration
nh = number of observations at the higher concentration
nl = number of observations at the lower concentration
4.8.3 For seven replicates at each concentration, the 90th
percentile of the distribution of the F-statistic is 3.055.
4.8.3.1 If seven replicates were analyzed at each spike
concentration and F 3.055, the two variances are
different and the MDL determined at the higher spike concentration
is not a reasonable estimate. In this case, return to section 4.3
and produce another sample at a test concentration below the higher
of the two previous iterations, analyze a minimum of seven aliquots,
calculate the MDL, and repeat the F-test in section 4.8.2.
4.8.3.2 If F <= 3.055 for seven replicates at each
concentration, the two variances are not different. Proceed to
section 4.8.4.
Note to Section 4.8.3.2: If more than seven replicates are used,
the appropriate F-statistic is determined from the table below.
[[Page 11789]]
Table of F-Statistic Values
----------------------------------------------------------------------------------------------------------------
F-statistic
---------------------------------------------------
6 7 8 9
----------------------------------------------------------------------------------------------------------------
6........................................................... 3.055 3.014 2.983 2.958
7........................................................... 2.827 2.785 2.752 2.725
8........................................................... 2.668 2.624 2.589 2.561
9........................................................... 2.551 2.505 2.469 2.440
----------------------------------------------------------------------------------------------------------------
4.8.4 When the process has been iterated and the results pass
the F-test in section 4.8.3, the final MDL is calculated by pooling
the results from the two iterations that passed the F-test. The
pooled standard deviation is calculated as:
[GRAPHIC] [TIFF OMITTED] TP12MR03.051
Where:
(sh)\2\ = variance estimate from the higher spike
concentration
(sl)\2\ = variance estimate from the lower spike
concentration
nh = number of sample aliquots used for the higher spike
concentration
nl = number of sample aliquots used for the lower spike
concentration
4.8.5 The pooled MDL is calculated using the pooled standard
deviation and the Student's t-value for (nh +
nl-2) degrees of freedom (e.g., 12 degrees of freedom for
two iterations with seven aliquots each).
[GRAPHIC] [TIFF OMITTED] TP12MR03.052
Where:
Spooled = pooled standard deviation of the results
t(nh + n1-2, 1-[alpha] = 0.99) =
Student's t-value appropriate for a 99% confidence level and
(nh+nl) aliquots
For 12 degrees of freedom, the t-value is 2.681. If more than
seven replicates were used for either iteration, the appropriate t-
value must be determined from the table given in section 4.7.
4.8.5 When verifying a method-, matrix-, program-, or study-
specific MDL, the determined MDL is compared to the method-specified
MDL, the MDL required to support a regulatory objective, or the MDL
required to support an objective of a specific study or program. If
the required MDL is not met for the analyte, make sure that all
instrumentation and technical aspects of the process (reagent
concentrations, temperature, clean glassware, proper dilutions,
etc.) are checked and assessed to be working properly before a
repeat of the analyses. If the second attempt fails, iteration at a
more appropriate spiking level for that analyte is necessary until
the requirement is met. If the regulatory, study, or program
objective is not known, the MDL is verified if the determined MDL is
less than or equal to the method-specified MDL.
4.9 Suspected Outliers
4.9.1 Results associated with a known, spurious error that
occurred during analysis should be discarded, or where appropriate,
corrected. Spurious errors include those that arise through human
error or instrument malfunction, such as transposing digits in a
number while recording data, arithmetical errors when calculating
results, double-spiking of an aliquot, or the presence of an air
bubble lodged in a spectrophotometer flow-through cell. Recording or
arithmetical errors can and should be corrected, and the corrective
actions documented prior to use of results. Results associated with
spurious errors that cannot be corrected will invalidate the
measurement and should not be incorporated into the MDL
determination.
4.9.2 If random or spurious errors are suspected, it may be
appropriate to apply a statistically accepted analysis of outliers,
such as Grubbs test described below. Any outlying result should be
considered with care to identify potential causes. It is generally
not an accepted practice to reject a value purely on statistical
grounds. Therefore, EPA recommends that when the cause of a
potential outlier cannot be attributed to spurious causes, the MDL
test be repeated for the analyte(s) in which such an outlier occurs.
Note to Section 4.9.2: If more than seven aliquots are prepared
and analyzed, results from all aliquots must be used in the MDL
determination unless they have been determined to be outliers as
described above. Given the small number of replicates typically used
to determine the MDL, it is inappropriate to use a data set that
contains more than one statistical outlier.
4.9.3 The use of Grubbs test for outliers is described below,
followed by an example (section 4.9.4).
4.9.3.1 Rank the n observed data points in the order of
increasing numerical value: X1 <= X2
<=...<=Xn
4.9.3.2 Using the mean, X, and standard deviation, s, from
section 4.6, calculate:
[GRAPHIC] [TIFF OMITTED] TP12MR03.053
Where:
X1 = lowest observed value of X
Xn = highest observed value of X
4.9.3.3 Choose the larger of T1 and Tn.
4.9.3.4 Compare the larger calculated value of T (e.g.,
T1 or Tn) with the critical value appropriate
for the number of observations (n) from the table below. If T is
larger than the critical value in the table, then the smallest (when
testing T1) or largest (when testing Tn)
observed data point is considered to be an outlier with 95%
confidence.
Table of Critical Values for T in the Grubbs Test
------------------------------------------------------------------------
Critical
Number of data points (n) values for T
------------------------------------------------------------------------
7....................................................... 2.020
8....................................................... 2.126
9....................................................... 2.215
10...................................................... 2.290
11...................................................... 2.355
12...................................................... 2.412
13...................................................... 2.462
14...................................................... 2.507
15...................................................... 2.549
------------------------------------------------------------------------
4.9.4 Example application of the outlier test
4.9.4.1 Consider the following ranked data set with seven
observations: 0.0449, 0.0458, 0.0462, 0.0469, 0.0471, 0.0475, and
0.0508.
4.9.4.2 Its mean, X, is 0.0470, and its standard deviation, s,
is 0.0019.
4.9.4.3 Calculate: T1 = (0.0470-0.0449)/0.0019 =
1.132 and Tn = (0.0508-0.0470)/0.0019 = 2.007
4.9.4.4 Select the larger value: T = max{1.132, 2.007{time} =
2.007
4.9.4.5 Compare T with the corresponding critical value in the
second line of the table above, where n=7 and the critical value of
T = 2.020.
Since the calculated value of T, 2.007, is not larger than the
critical value in the table, 2.020, there is insufficient evidence
to conclude that any of the observed data points is an outlier, and
the MDL would be calculated from all seven results.
5.0 References
5.1 Currie, Lloyd A. (1968), Limits for Quantitative Detection
and Quantitative Determination, Analytical Chemistry 40: 586-593.
5.2 Currie, Lloyd A. (1995), Nomenclature in Evaluation of
Analytical Methods including Detection and Quantification
Capabilities, Pure and Appl. Chem. 67:10, 1699-1722.
5.3 Glaser, J.A., D.L. Foerst, J.D. McKee, S.A. Quave and W.L.
Budde (1981), Trace Analyses for Wastewaters, Environ. Sci.
Technol., 15:1426.
5.4 Keith, Lawrence H., et al. (1983), Principles of
Environmental Analysis, Analytical Chemistry 55:14, 2210-2218.
5.5 McDougal, Daniel, et al. (1980), Guidelines for Data
Acquisition and Data Quality Evaluation in Environmental Chemistry,
Analytical Chemistry 52:14, 2242-2249.
[[Page 11790]]
B. Definition and Procedure for the Determination of the Minimum Level
of Quantitation (ML)
1.0 Definition
The minimum level of quantitation (ML) is the lowest level at
which the entire analytical system gives a recognizable signal and
acceptable calibration point for the analyte. The ML represents the
lowest concentration at which an analyte can be measured with a
known level of confidence. It may be equivalent to the concentration
of the lowest calibration standard, assuming that all method-
specified sample weights, volumes, and cleanup procedures have been
employed. It is functionally analogous to the ``determination
limit'' described by Currie (1968) and the Limit of Quantification
(LOQ) described by the American Chemical Society (Keith et al.,1980,
McDougal et al., 1983) and Currie (1995).
Note to Section 1.0: The ML is directed at obtaining a 10%
relative standard deviation for determination of an analyte in an
environmental sample. This error may be reduced by making multiple
determinations of the analyte in the sample.
2.0 Scope and Application
2.1 The ML is typically established by the organization that
develops or modifies an analytical test method. A laboratory that
employs the method would be expected to include calibration
standards that encompass the ML when it calibrates an analytical
system, unless a higher quantitation level is acceptable for a
specific application. If an ML is not specified in a method, a
laboratory may use the ML procedure to establish the lowest
calibration point.
2.2 This procedure is intended for use in EPA's Clean Water Act
(CWA) programs. An alternative procedure may be used (e.g., from a
voluntary consensus standards body) to establish the sensitivity of
an analytical method provided the resulting quantitation limit meets
the sensitivity needs (i.e., data quality objective) for the
specific application.
2.3 Laboratories are encouraged, but not required, to
periodically demonstrate recovery of the target analyte near the
published ML or laboratory-established ML by preparing a reference
matrix sample spiked at the ML and analyzing it using all sample
handling and processing steps described in the method. If the method
does not provide acceptance criteria for such an ML standard, the
laboratory can make an assessment of whether acceptance criteria for
other spiked reference matrix samples (e.g., laboratory control
samples, laboratory fortified blanks, ongoing precision and recovery
samples, etc.) are appropriate to evaluate analyte recovery at the
ML. Alternatively, the laboratory may develop its own acceptance
criteria based on data gathered by the laboratory over time.
3.0 Procedure
3.1 The ML is based on 10 times the standard deviation of the
results of replicate analyses of a matrix containing the analyte.
The method detection limit (MDL) is also based on the same standard
deviation, multiplied by the Student's t-value appropriate for a 99%
confidence level and corresponding degrees of freedom. Because the
standard deviation may not be readily available, the ML is often
calculated as a factor times the MDL.
3.1.1 Calculating the ML based on MDL study data
When available, obtain the actual standard deviation value from
the MDL study and calculate the ML directly, as 10 times the
standard deviation. If an iterative MDL study is performed,
calculate the MDL as 10 times the pooled standard deviation.
3.1.2 Calculating the ML based on the MDL Assuming a single
iteration of seven replicates is used to determine the MDL, the
number of degrees of freedom is 6, and the Student's t-value is
3.143. Therefore, the MDL is:
MDL = 3.143 x s
and the ML is:
[GRAPHIC] [TIFF OMITTED] TP12MR03.054
3.1.3 If the MDL is calculated from other than seven replicates
or using the iterative procedure, the factor of 3.18 will change,
and the table below is used to establish the correct multiplier. For
example, if an iterative MDL study is performed consisting of
exactly 7 replicates in each iteration, the resulting pooled MDL
would incorporate 12 degrees of freedom, and the equation for the ML
above would be modified accordingly, using a multiplier of 3.73.
Table of Student's t-values at the 99% Confidence Level and ML Multipliers
----------------------------------------------------------------------------------------------------------------
Number of replicates for
-------------------------------------------------------------- Degrees of ML
Iterative MDL freedom (df) t(n-1,1-[alpha]=0.99) multiplier
Single MDL (df=n-1) (df=n-2)
----------------------------------------------------------------------------------------------------------------
7............................................ N/A 6 3.143 3.18
8............................................ N/A 7 2.998 3.34
9............................................ N/A 8 2.896 3.45
10........................................... N/A 9 2.821 3.54
11........................................... N/A 10 2.764 3.62
12........................................... N/A 11 2.718 3.68
13........................................... 14 12 2.681 3.73
14........................................... 15 13 2.650 3.77
15........................................... 16 14 2.624 3.81
16........................................... 17 15 2.602 3.84
17........................................... 18 16 2.583 3.87
18........................................... 19 17 2.567 3.90
19........................................... 20 18 2.552 3.92
----------------------------------------------------------------------------------------------------------------
Note to Table: Degrees of freedom = (n-1) if a single iteration
MDL study is performed and (nh + nl-2) if an
iterative MDL study is performed; N/A indicates that the number of
degrees of freedom in this row does not apply to an iterative MDL
study.
4.0 Rounding
The ML may be used to establish the lowest calibration point for
the analyte. Therefore, in order to facilitate the preparation of
calibration standards containing the analyte without undue
difficulty, the ML may be rounded to the nearest multiple of 1, 2,
or 5 x 10 n, where n is an integer.
5.0 References
5.1 Currie, Lloyd A. (1968), Limits for Quantitative Detection
and Quantitative Determination, Analytical Chemistry 40: 586-593.
5.2 Currie, Lloyd A. (1995), Nomenclature in Evaluation of
Analytical Methods including Detection and Quantification
Capabilities, Pure and Appl. Chem. 67:10, 1699-1722.
5.3 Glaser, J.A., D.L. Foerst, J.D. McKee, S.A. Quave and W.L.
Budde (1981), Trace Analyses for Wastewaters, Environ. Sci.
Technol., 15:1426.
5.4 Keith, Lawrence H., et al. (1983), Principles of
Environmental Analysis, Analytical Chemistry 55:14, 2210-2218.
5.5 McDougal, Daniel, et al. (1980), Guidelines for Data
Acquisition and Data Quality Evaluation in Environmental Chemistry,
Analytical Chemistry 52:14, 2242-2249.
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