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Review of the U.S. Army's Health Risk Assessments for Oral Exposure to Six Chemical-Warfare Agents 1 Introduction IN 1985, the U.S. Congress passed Public Law 99–145 requiring the destruction of the stockpile of lethal chemical-warfare agents and munitions in the United States. Two principal types of chemical-warfare agents are found at U.S. stockpile sites—nerve agents (e.g., GB and VX) and vesicating (blistering) agents (e.g., sulfur mustard agents). Chemical stockpile sites are located at nine sites: Umatilla Depot, Oregon; Tooele Army Depot, Utah; Pueblo Depot, Colorado; Newport Army Ammunition Plant, Indiana; Aberdeen Proving Ground, Maryland; Lexington-Blue Grass Army Depot, Kentucky; Anniston Army Depot, Alabama; Pine Bluff Arsenal, Arkansas; and Johnston Atoll in the Pacific Ocean. Some chemical-warfare agents and related materiel, referred to as nonstockpile chemical materiel (NSCM), were not included in the 1985 law requiring destruction but were subsequently added to the chemical demilitarization program in the House Appropriations Report 101–822 that accompanied the fiscal year 1991 Defense Appropriations Act. NSCM includes lethal wastes from past disposal efforts, unserviceable munitions, chemically contaminated containers, chemical-production facilities, newly located chemical munitions, known sites containing significant quantities of buried chemical weapons and waste, and binary weapons and components. The U.S. Army has identified 82 NSCM locations in the United States, involving 33 states, the Virgin Islands, and the District of Columbia (Opresko et al. 1998). Table 1–1 presents a list
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Review of the U.S. Army's Health Risk Assessments for Oral Exposure to Six Chemical-Warfare Agents TABLE 1–1 Summary of Chemical Materiel Thought to Be Located at Nonstockpile Sitesa State—EPA Region Site Material of Concernb Alabama—IV Anniston Army Depot GB, VX Ft. McClellan GB, VX, mustard, HD, CK, CG, BZ, CX, AC Camp Sibert Mustard degradation products Huntsville Arsenal Mustard Redstone Arsenal HD, L, uncharacterized rounds, GB, VX Theodore Naval Ammunition Magazine Mustard and/or its degradation products Alaska—X Adak Mustard, L Chicago Harbor Mustard, L Gerstle River Test Center Mustard, L, GB, GA, VX Unalaska Island CAISc vials Ft. Wainwright CAISc Arizona—IX Navajo Depot Activity Mustard, white phosphorus, PWP Yuma Proving Ground Mustard, GB, VX Arkansas—VI Ft. Chaffee CAISc residue Pine Bluff Arsenal Mustard, HN, L, and degradation products, CAISc California—IX Ft. Ord Mustard, CAISc Santa Rosa Army Airfield CAISc Edwards AFB Mustard, GB, phosgene, CK, HCN Colorado—VII Rocky Mountain Arsenal GB, mustard, CG, VX Pueblo Army Depot Activity Mustard District of Columbia—III American University L, adamsite Florida—IV Brooksville Army Air Base Mustard Drew Field Mustard, CAISc MacDill AFB Mustard Withlacoochee Mustard (Levinstein) Dry Tortuga Keys Mustard Zephyr Hills Gunner Range Mustard Georgia—IV Ft. Gillem Mustard Ft. Benning G-agents Manchester Mustard Hawaii—IX Kipapa Ammunition Storage Site Mustard Schofield Barracks H, L, CK, HCN, and residues, CAISc GB, BZ Waiakea Forest Reserve CAISc GB, BZ Idaho—X Targhee National Forest Phosgene, NO2 Illinois—V Savanna Army Depot Activity Mustard and residue
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Review of the U.S. Army's Health Risk Assessments for Oral Exposure to Six Chemical-Warfare Agents State—EPA Region Site Material of Concernb Indiana—V Camp Atterbury Mustard, CAISc Naval Weapons Support Center Mustard, CAISc Newport Army Ammunition Plant VX and residue Kansas—VII Marysville Mustard Kentucky—IV Blue Grass Army Depot Mustard Louisiana—VI England AFB CAISc, phosgene Ft. Polk CAISc (mustard, L) Mississippi River near New Orleans Bombs with unknown fill Concord Spur Mustard Maryland—III Edgewood Area-APG VX, mustard, GA, GB, white phosphorus, riot control agents; spectrum of US, foreign, and experimental CW Mississippi—IV Columbus Army Airfield Mustard Horne Island Mustard, arsenic-containing agents, unspecified others Camp Shelby Mustard Nebraska—VII Nebraska Ordnance Plant Mustard Nevada—IX Hawthorne Army Ammunition Plant Mustard, phosgene, unspecified others New Jersey—II Lakehurst Naval Air Base Unspecified ''toxic agent shells" Raritan Arsenal Mustard and residues Delaware Ordnance Depot Phosgene Ft. Hancock Unspecified "gas storage cylinders" New Mexico—VI Wingate Ordnance Depot Mustard New York—II Mitchel Field CAISc North Camp LeJeune CAISc, CN, unspecified others Carolina—IV Laurinburg-Maxton Army Air Base Mustard Ohio—V Ravenna Army Ammunition Plant Mustard Oregon—X Umatilla Depot Activity Mustard, VX, other "mixed contamination" Pennsylvania—III Defense District Region East (formerly New Cumberland Army) CAISc South Charleston Army Depot Mustard Carolina—IV Naval Weapons Center Mustard
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Review of the U.S. Army's Health Risk Assessments for Oral Exposure to Six Chemical-Warfare Agents State—EPA Region Site Materiel of Concernb South Dakota—VIII Black Hills Ordnance Depot Mustard, CG Tennessee—IV Defense Depot Memphis Mustard, CAISc Texas—VI San Jacinto Ordnance Depot Phosgene, mustard Ft. Hood Mustard, CN Camp Stanley Storage Activity Mustard Camp Bullis Mustard, CN, CS, phosgene, PS, white phosphorus Utah—VIII Dugway Proving Ground VX, GA, GB, GD, CS, mustard, agent residues, foreign chemical munitions, unspecified others; biologicals Defense Depot Ogden CAISc, mustard, phosgene, smoke bombs Tooele Army Depot Mustard and residues, smoke pots, GA, incendiaries Virginia—III Ft. Belvoir CAISc Washington—X U.S. Naval Magazine Phosgene Virgin Islands—II (Former) Ft. Segarra (St. Thomas, Water Island) CG, CK, HCN, phosgene, H, HT, GA a Data from USACMDA (1993a,b). b GA, GB, GD, and VX are organophosphate nerve agents with anticholinesterase properties; H, HD, and HT are various formulations of sulfur mustard (vesicant); HN is nitrogen mustard (vesicant); L is the organic arsenical vesicant, lewisite. The following are less common: adamsite is an organic arsenical vomiting agent; AC is hydrogen cyanide (HCN); BZ is 3-quinuclidinyl benzilate, a hallucinogen; CK is the casualty agent cyanogen chloride; CG is phosgene (carbonyl chloride), a choking agent; CX is phosgene oxime (vesicant); CN is chloroacetophenone ("tear gas") and is used as a riot-control agent; CS is o-chlorobenzalmalononitrile ("tear gas") and is used as a riot-control agent. c Chemical Agent Identification Set, a training aid containing vials of various chemical-warfare agents normally in dilute chloroform solution. Source: Opresko et al. 1998. of specific sites and the chemical materiel present at those sites. Sulfur mustard agents is the most frequently identified materiel. Historically, disposal of chemical-warfare agents was accomplished through burial, although some NSCM was placed in bodies of water. Thus, there is potential for soil and groundwater contamination at many of the NSCM sites.
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Review of the U.S. Army's Health Risk Assessments for Oral Exposure to Six Chemical-Warfare Agents In the past, the destruction of NSCM was not addressed as intensely as the disposal of existing chemical-weapon stockpiles, because most NSCM sites do not pose an immediate risk to public health or the environment. However, the urgency for destroying NSCM has recently increased because of the discovery of buried NSCM and the signing of the chemical-arms-control treaty (Convention on the Prohibition of the Development, Production, Stockpiling, and Use of the Chemical Weapons and on Their Destruction) by the United States and 150 other nations to eliminate chemical weapons from the inventories of all nations. The 1993 Defense Authorization Act (Section 176 of Public Law 102–484) directed the Army to examine the scale of effort and to consider plans needed to dispose of NSCM. The NRC's Board on Army Science and Technology is involved in studies of the destruction of stockpile and nonstockpile chemical munitions. The Committee on Review and Evaluation of the Army Chemical Stockpile Disposal Program and the Committee on Review and Evaluation of the Army Chemical Non-Stockpile Materiel Disposal Program are reviewing the technical aspects of the Army's disposal methods on an ongoing basis (see NRC 1999a, b). The U.S. Army Environmental Center (USAEC) serves as the program manager for the Army's Installation Restoration Program and is involved in the Army Base Realignment and Closure program. It has responsibilities for supporting installation-restoration (environmental cleanup) activities at Army installations and property nationwide. The USAEC and the Army Corps of Engineers investigate, characterize, and remediate sites where contamination is found. In recent years, there has been an increasing need for decision-making criteria to determine the scale of installation restoration required at active military installations and formerly used defense sites where chemical-warfare agent contamination has occurred. The goal of the restoration efforts is to ensure that chemical contamination is reduced to safe concentrations in these areas before they are used for residential, occupational, or wildlife purposes. Therefore, health-based exposure limits must be established to protect the public and the environment. Although people can be exposed to chemical-warfare agents in different ways, including ingestion of contaminated drinking water or soil, inhalation of vapors or contaminated dust, and dermal contact from contaminated soil, the subcommittee was asked to consider only the oral pathway. Reference doses (RfDs) are toxicological values used as reference points to limit human oral exposure to potentially hazardous amounts of
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Review of the U.S. Army's Health Risk Assessments for Oral Exposure to Six Chemical-Warfare Agents chemicals that are thought to have thresholds for their effects. An RfD is an estimate (with uncertainty spanning an order of magnitude or greater) of the daily oral exposure to a potential toxicological hazard that is likely to have no risk of deleterious effects during a human lifetime (EPA 1989). The RfD is derived by identifying the no-observed-adverse-effect level or lowest-observed-adverse-effect level from animal and human studies, and dividing by uncertainty factors, that reflect the uncertainties associated with the types of data used, and a modifying factor, that is based on a professional judgment of additional uncertainties not addressed by the standard uncertainty factors. For those chemicals identified as carcinogens (e.g., sulfur mustard), slope factors (SFs) are derived in addition to RfDs. An SF is the slope of the dose-response curve for an agent in the low-dose region. An SF is used to estimate the lifetime cancer risk from chronic exposure to an agent and is typically determined by modeling an agent's dose-response curve as the doses approach zero. An upper-bound on the slope is usually used instead of the slope itself. For agents that do not have an appropriate chronic toxicity study from which to model a dose-response curve, SFs can be determined by comparing the carcinogenic potency of an agent with that of a well-known carcinogen. The Army uses RfDs and SFs to make site-specific decisions on cleanup of sites contaminated with chemical-warfare agents and to make decisions on the potential uses of military installations. Because RfDs and SFs are applicable to the oral exposure route, they are used to calculate exposure limits for drinking water, soil, and other media that have the potential to be ingested by persons at or near remediation sites. Although RfDs and SFs can be applied to more than one site, exposure limits are more appropriately determined on a site-specific basis. RfDs and SFs are not media (e.g., water and soil) standards for purposes of safe cleanup or decontamination goals. RfDs and SFs are translated into safe media concentrations by incorporating information on site-specific exposure variables, including exposure frequency; exposure duration; estimated amount of contaminated soil, water, or specific food ingested; ingestion rate; and body weight. The site-specific exposure variables and the RfD or SF are incorporated into a health risk assessment according to approved methods and calculations of the U.S. Environmental Protection Agency (EPA). Thus, safe public and environmental standards are calculated from the RfD or SF and are dependent on the situation. At the request of the Army, Oak Ridge National Laboratory conducted
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Review of the U.S. Army's Health Risk Assessments for Oral Exposure to Six Chemical-Warfare Agents health risk assessments and derived RfDs for six chemical-warfare agents—GA, GB, GD, VX, sulfur mustard, and lewisite—and an SF for sulfur mustard (see Appendices A–F). These agents are considered priority chemicals, because they are the ones most commonly found at stockpile and NSCM sites. GA, GB, GD, and VX are nerve agents, and lewisite and sulfur mustard are vesicating (blistering) agents. Because immediate establishment of the RfDs and SFs for those agents was believed to be necessary to ensure that consistent, health-based criteria would be applied in ongoing initiatives requiring decisions on the safety of contaminated sites, the Army's Surgeon General accepted the proposed RfDs and SFs as interim values until an independent review of them was conducted by the National Research Council (NRC). In 1996, the Army requested that the NRC review the scientific validity of the RfDs and SFs for the six chemical-warfare agents. The NRC assigned this task to the Committee on Toxicology (COT), which assembled the Sub-committee on Chronic Reference Doses for Selected Chemical-Warfare Agents to review the scientific validity of the RfDs developed for GA, GB, GD, VX, lewisite, and sulfur mustard and the SF for sulfur mustard. The multidisiplinary subcommittee of experts was asked to (1) determine whether all the relevant toxicity data were appropriately considered; (2) review the uncertainty, variability, and quality of data; (3) determine the appropriateness of the assumptions used to derive RfDs (e.g., application of uncertainty factors); and (4) identify data gaps and make recommendations for future research. To address its task, the subcommittee critically reviewed the health-risk-assessment documents on the individual chemical-warfare agents provided by the Army (see Appendices A–F, which were published in 1998 by Opresko et al.), published and unpublished studies cited in the Army's reports, and conducted its own literature search to identify any relevant data that were missing. Although the potential exists for multiple agents to be present at NSCM sites, the subcommittee was asked to evaluate the agents only on an individual basis. Furthermore, although the most likely routes of exposure to chemical-warfare agents at stockpile and NSCM sites are the inhalation and dermal routes, the subcommittee was only asked to evaluate toxicological risk from the oral route of exposure at this time. The Army informed the subcommittee that inhalation exposure guidelines are in development. The subcommittee was not asked to address issues related to risk management, such as technology, detection, and feasibility.
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Review of the U.S. Army's Health Risk Assessments for Oral Exposure to Six Chemical-Warfare Agents The results of the subcommittee's evaluations are presented in Chapters 2 through 9. Chapter 2 reviews the method used by the Army to derive RfDs, and also includes a discussion of the benchmark dose method as a point of departure for calculating RfDs. Chapters 3 through 6 evaluate the RfDs for the nerve agents GA, GB, GD, and VX. Chapter 7 evaluates the RfD and slope factor for sulfur mustard, and Chapter 8 provides an evaluation of the RfD for lewisite. Research recommendations are presented at the end of Chapters 3–8 for each of the specific chemical-warfare agents. REFERENCES EPA (U.S. Environmental Protection Agency). 1989. Risk Assessment Guidance for Superfund, Vol. I, Human Health Evaluation Manual (Part A), Interim Final. EPA/540/1-89/002. U.S. Environmental Protection Agency, Office of Emergency and Remedial Response, Washington, D.C. NRC (National Research Council). 1999a. Carbon Filtration for Reducing the Emissions from Chemical Agent Incineration. Washington, D.C.: National Academy Press. NRC (National Research Council). 1999b. Tooele Chemical Agent Disposal Facility: Update on National Research Council Recommendations. Washington, D.C.: National Academy Press. Opresko, D.M., R.A. Young, R.A. Faust, S.S. Talmage, A.P. Watson, R.H. Ross, K.A. Davidson, and J. King. 1998. Chemical warfare agents: Estimating oral reference doses. Rev. Environ. Contam. Toxicol. 156:1–183. USACMDA (U.S. Army Chemical Materiel Destruction Agency). 1993a. Interim Survey and Analysis Report. Program Manager for Nonstockpile Chemical Materiel, Nonstockpile Chemical Materiel Program, U.S. Department of the Army, Chemical Materiel Destruction Agency, Aberdeen Proving Ground, Edgewood, Md. USACMDA (U.S. Army Chemical Materiel Destruction Agency). 1993b. Survey and Analysis Report. Program Manager for Nonstockpile Chemical Materiel, Nonstockpile Chemical Materiel Program, U.S. Department of the Army, Chemical Materiel Destruction Agency, Aberdeen Proving Ground, Edgewood, Md.
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