[Federal Register Volume 68, Number 180 (Wednesday, September 17, 2003)]
[Notices]
[Pages 54460-54462]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 03-23683]


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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

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 
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

[[Page 54461]]

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/m\3\. 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 bases 
of these comments, CDC has adjusted the VX short-term exposure limit 
(STEL) to 1 x 10-\5\ mg/m\3\ 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-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 above the WPL up 
to 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

[[Page 54462]]

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.

                 Table 1.--Final Recommended Airborne Exposure Limits (AELs) for GA, GB, and VX
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                                                                                                  Immediately
                                  General population   Worker population      Short-term       dangerous to life
          AEL (mg/m3)                limit (GPL)*        limit (WPL)*       exposure limit     or health (IDLH)
                                                                           (STEL)* (Workers)       (Workers)
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GA, GB.........................  1 x 10-6...........  3 x 10-5..........  1 x 10-4..........  0.1.
GA, GB--Previous (1988)........  3 x 10-6...........  1 x 10-4..........  ..................  0.2 (Army)
VX.............................  6 x 10-7...........  1 x 10-6..........  1 x 10-5 **.......  0.003
VX--Previous (1988)............  3 x 10-6...........  1 x 10-5..........  ..................  0.02 (Army)
Averaging time.................  24 hours...........  8 hours...........  15 minutes........  = 30 minutes
Monitoring Method for            Historical monitor   Historical monitor  Near-real-time      Near-real-time
 Recommended Exposure Criteria.   ***.                                     monitor.            monitor
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* An additional reduction factor for statistical assurance of action at the exposure limit is not needed because
  of safety factors already built into the derivation of the exposure limit.
** VX STEL has been adjusted from 4 x 10-6 mg/m3 (up to four times per day) as proposed in the Federal Register
  announcement to 1 x 10-5 mg/m3 (not more than one time per day) based on technical capabilities of existing
  air-monitoring technologies.
*** Historical monitoring typically refers to long-term sampling and analytical methods. Air-monitoring results
  from historical methods are not known until laboratory analyses are complete. 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: September 11, 2003.
Alvin Hall,
Director, Management Analysis and Services Office, Centers for Disease 
Control and Prevention.
[FR Doc. 03-23683 Filed 9-16-03; 8:45 am]
BILLING CODE 4163-18-P