[Federal Register: October 9, 2003 (Volume 68, Number 196)]
[Notices]
[Page 58348-58351]
From the Federal Register Online via GPO Access [wais.access.gpo.gov]
[DOCID:fr09oc03-90]
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DEPARTMENT OF HEALTH AND HUMAN SERVICES
Centers for Disease Control and Prevention
Final Recommendations for Protecting Human Health From Potential
Adverse Effects of Exposure to Agents GA (Tabun), GB (Sarin), and VX
The National Center for Environmental Health published a document
in the September 17, 2003, edition (Volume 68, Number 180, Pages 54460-
54462) of the Federal Register entitled ``Final Recommendations for
Protecting Human Health from Potential Adverse Effects of Exposure to
Agents GA (Tabun), GB (Sarin), and VX.'' A printing error altered a
value in Table 1. The error has since been corrected. The document is
being republished in its entirety for the convenience of the reader.
AGENCY: Centers for Disease Control and Prevention (CDC), Public Health
Service, Department of Health and Human Services.
ACTION: Notice of final recommendations for protecting human health
from potential adverse effects of exposure to agents GA, GB, and VX.
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SUMMARY: Agents GA, GB, and VX are stored and are in the process of
being destroyed by the Department of Defense (DoD). Public Law 99-145
(50 U.S.C. 1521) mandates that all unitary (self-contained) lethal
chemical munitions be destroyed. Public Law 91-121 and Public Law 91-
441 (50 U.S.C 1512) mandate that the Department of Health and Human
Services (DHHS) review DoD plans for disposing of these munitions and
make recommendations to protect public health.
EFFECTIVE DATE: January 1, 2005. An implementation period is necessary
to allow the DoD to make program adjustments and allow time for changes
to environmental permits as required.
FOR FURTHER INFORMATION CONTACT: Dr. Paul Joe, Acting Chief, Chemical
Demilitarization Branch, National Center for Environmental Health, CDC,
4770 Buford Highway, M/S F-16, Atlanta, Georgia 30341.
SUPPLEMENTARY INFORMATION: On January 8, 2002, DHHS, CDC published
[[Page 58349]]
proposed ``Airborne Exposure Limits for Chemical Warfare Agents GA
(tabun), GB (sarin) and VX'' in the Federal Register (Vol. 67, No. 5,
Pages 894-901, Tuesday, January 8, 2002), seeking public comment. This
notice discusses major comments received, describes decisions regarding
the public comments, and states the final recommendations. CDC received
comments from the U.S. Army, the Agency for Toxic Substances and
Disease Registry (ATSDR), the CDC's National Institute for Occupational
Safety and Health (NIOSH), state of Utah, U.S. Army contractors, and
two individuals.
The comments fell into the following general categories:
assumptions used in the risk assessment, selection of uncertainty
factors, determination of the relative potency factor for the VX
exposure limits, and technical feasibility of air monitoring at the
lower exposure limits. The key comments potentially impacting CDC's
recommendations are discussed below.
The U.S. Army recommended that adjustment in the risk assessment
algorithm for breathing rate be eliminated because the critical
endpoint in deriving the exposure limits is miosis, a clinical sign
that is recognized as a local effect on the muscles of the iris of the
eye. This biologic endpoint is widely considered to be a direct effect
of the nerve agent vapor on the surface of the eye (not related to
breathing rate). Scientists from CDC/NIOSH however, indicated that the
data do not completely rule out the potential contribution of inhaled
agent to the miosis effect. The weight of the scientific data appears
to support the Army's recommendation on this matter, and CDC has
decided to eliminate the breathing rate adjustment. Eliminating the
breathing rate adjustment increases the worker population limit (WPL)
by a factor of slightly more than two. No significant change in the
general population limit (GPL) would occur by eliminating the breathing
rate adjustment.
In the derivation of the WPL for GB, CDC/NIOSH experts recommended
that an additional uncertainty factor of three be added to account for
individual worker variability. Although workers are medically screened,
the recommendation is a reasonable public health decision. CDC
therefore has incorporated the additional uncertainty factor of three
into the risk assessment algorithm. Making this adjustment lowers the
exposure limits by a factor of three. This adjustment and elimination
of the breathing rate factor suggested above essentially cancel each
other.
In the derivation of the VX exposure limits by using relative
potency, the Army questioned the use of a relative potency of 12 with
the application of a modification factor of three for the incomplete VX
data set. The application of a relative potency of 12 with a modifying
factor of three effectively resulted in a relative potency of 36
between the calculated exposure limits for GB and VX. As discussed in
the January 8, 2002, Federal Register proposal, the relative potency
factor of 12 was based on a 1971 British study that measured the
ability of VX to cause 90 percent pupil constriction in rabbits.
Because the critical effect in the study used to derive the GB exposure
limit was miosis, CDC believes that miosis was appropriate to use as
the health effect in determining the relative potency of VX. CDC/NIOSH
experts and the state of Utah supported the proposed relative potency
of 12 with a modifying factor of three. Therefore, CDC is retaining its
relative potency assumptions for deriving the VX exposure limits.
As discussed in the January 8, 2002, Federal Register proposal, CDC
adjusted the VX GPL because available air-monitoring methods do not
reliably detect VX at the calculated value of 3 x 10-\8\ mg/
m3. In the adjustment, CDC assumed that potential exposure
would be identified and corrected within three days, precluding chronic
exposure. Several people who provided comments pointed out that a
similar adjustment also could have been made for the GB GPL. CDC
recognizes that the assumptions used to derive the GPLs for GB and VX
differ. Indeed, this adjustment could be applied to the GB exposure
limits; however, the air-monitoring technology is currently functioning
near the recommended level. CDC recommends no upward adjustment of the
GB exposure limits; this recommendation is consistent with the accepted
industrial hygiene practice of keeping exposure to the minimum
practicable level.
The derivation of the VX exposure limits may be biased low because
of the inadequate VX toxicity database. CDC believes that reliable air
monitoring is a crucial aspect for implementing the exposure limits.
Although CDC would have preferred a better toxicity database for VX, as
well as improved air-monitoring methods for VX, these items are not
currently available. Consequently, CDC is not further adjusting the
final recommendation to the GPL for VX. However, CDC will reevaluate
the VX exposure limits in the future if significant new VX toxicity
data are available for setting exposure limits, new risk assessment
evaluation methods are demonstrated superior to methods used herein, or
substantive technological advances in air monitoring methods are made.
Army contractors and CDC/NIOSH experts expressed concerns about the
technical feasibility of meeting the new exposure limits. On the basis
of these comments, CDC has adjusted the VX short-term exposure limit
(STEL) to 1 x 10-\5\ mg/m3 but added the
provision that excursions to this special VX STEL should not occur more
than once per day (in the typical STEL, four excursions per day are
allowed). A lower STEL value would have required a longer response time
for near real-time instruments; the recommended STEL is a result of
balancing the detection capabilities and response time. A shorter
instrument response time associated with the recommended STEL will
minimize exposures. This adjustment to the VX STEL should not affect
worker health.
To account for other technical feasibility concerns, CDC recommends
that the GB and VX STEL be evaluated with near-real-time
instrumentation, whereas the GB and VX WPLs and GPLs may be evaluated
with longer-term historical air monitoring methods. CDC further
recommends that, in implementing the WPLs, STELs and GPLs, specific
reduction factors for statistical assurance of action at the exposure
limits are not needed because of safety factors already built into the
derivation of the exposure limit. This recommendation assumes that the
sampling and analytical methods are measuring within +/-25% of the true
concentration 95% of the time. If this criterion is not met, an alarm
level or action level below the exposure limit may be required.
The Army recently indicated to CDC that the exposure limits as
listed and implemented in this announcement are technically feasible to
detect with the instrumentation and methods currently in use. However,
whether the agent destruction sites can monitor at these exposure
limits and still meet current quality control standards has not been
determined. To allow the Army to implement program changes, regulatory
adjustments, and to evaluate quality control issues, the final
recommended exposure limits will become effective January 1, 2005.
Final Recommendations: CDC presents final recommendations for
airborne exposure limits (AELs) for the chemical warfare agents GA
(tabun or ethyl N,N-dimethyl-phosphoramidocyanidate, CAS 77-81-6); GB
(sarin or O-isopropyl-
[[Page 58350]]
methylphosphonofluoridate, CAS 107-44-8); and VX (O-ethyl-S-(2-
diisopropylaminoethyl)-methylphosphonothiolate, CAS 50782-69-9). CDC
based its recommendations on comments by scientific experts at a public
meeting convened by CDC on August 23-24, 2000, in Atlanta, Georgia; the
latest available technical reviews; and the risk assessment approach
frequently used by regulatory agencies and other organizations.
Additionally, CDC reviewed the substantial background information
provided in the recent U.S. Army evaluations of the airborne exposure
criteria for chemical warfare agents. AELs for chemical warfare agents
GA, GB, and VX were reevaluated by using the conventional reference
concentration risk assessment methodology for developing AELs described
by the U.S. Environmental Protection Agency. This methodology is
considered conservative; however, the calculated exposure limits are
neither numerically precise values that differentiate between
nonharmful and dangerous conditions, nor are they precise thresholds of
potential human toxicity. The recommended changes to the AELs do not
reflect change in, nor a refined understanding of, demonstrated human
toxicity of these substances but rather the changes resulted from
updated and minimally modified risk assessment assumptions. Overt
adverse health effects have not been noted in association with the
previously recommended exposure limits. This may be due to rigorous
exposure prevention efforts in recent years as well as the conservative
implementation of the existing limits (i.e., 8-hour time-weighted
average exposure limits have been implemented as short-duration ceiling
values).
Recommended AELs for GB: CDC recommends a WPL value of 3 x
10-5 mg/m\3\, expressed as an 8-hour time-weighted average
(TWA). Additionally, CDC recommends a STEL of 1 x 10-4 mg/
m\3\ to be used in conjunction with the WPL. Exposures at the STEL
should not be longer than 15 minutes and should not occur more than
four times per day, and at least 60 minutes should elapse between
successive exposures in this range. The STEL should not be exceeded
during the work day, even if the cumulative exposure over the 8-hour
TWA is not exceeded. CDC recommends a decrease in the GPL to 1 x
10-6 mg/m\3\. The WPLs and GPLs values are approximately
threefold lower than levels previously recommended by CDC in 1988. An
immediately-dangerous-to-life-or-health (IDLH) value of 0.1 mg/m\3\ is
recommended for GB.
Recommended AELs for GA: Although not as well-studied as GB, GA is
believed to be approximately equal in potency to GB. Therefore, CDC
recommends the same exposure limits for GA as for GB.
Recommended AELs for VX: CDC recommends that the VX WPL, expressed
as an 8-hour TWA, be decreased to 1 x 10-6 mg/m\3\.
Additionally, CDC recommends a VX STEL of 1 x 10-5 mg/m\3\.
An excursion to the STEL should not occur more than one time per day
(compared to four times per day for a typical STEL). The recommended
WPL is a factor of 10 lower than the CDC's 1988 recommendation. CDC
recommends that the GPL for VX be decreased to 6 x 10-7 mg/
m\3\ (a factor of five lower than CDC's 1988 recommendation). An IDLH
value of 0.003 mg/m\3\ is recommended for VX. CDC's final
recommendations are summarized in Table 1 below.
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CDC does not specifically recommend the use of these AELs for uses
other than transportation, worker protection during the destruction
process, or general population protection. For example, the 8-hour WPL
historically has been used for the Army-designated 3X decontamination,
surveillance activities of leaking containers in storage, and charcoal
unit mid-beds. CDC did not evaluate the applicability of the WPLs for
these activities; the specific technical and safety requirements for
each activity need to be considered individually.
This announcement does not address the allowable stack
concentration (ASC). The ASC is a ceiling value that serves as a
destruction process source emission limit and not as a health standard.
It typically is used for monitoring the furnace ducts and final exhaust
stack, providing an early indication of an upset condition. Modeling of
worst-case credible events and conditions at each installation should
confirm that the WPL is not exceeded on-site or that the GPL is not
exceeded at the installation boundary as a consequence of a release at
or below the ASC.
The Director, Management Analysis and Services Office, has been
delegated the authority to sign Federal Register notices pertaining to
announcements of meetings and other committee management activities for
both CDC and ATSDR.
Dated: October 3, 2003.
Alvin Hall,
Director, Management Analysis and Services Office, Centers for Disease
Control and Prevention.
[FR Doc. 03-25583 Filed 10-8-03; 8:45 am]
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