Introduction and Background

For more than 50 years, the United States has maintained a stockpile of chemical agents and munitions distributed among eight sites within the continental United States and at Johnston Atoll in the Pacific Ocean. Two basic types of chemical agents comprise the stockpile: neurotoxic (nerve) agents and mustard (blister) agents. Both types are frequently, and erroneously, referred to as "gases" even though they are liquids at normal temperature and pressure.

The nerve agents include the organic phosphorus compounds designated as VX, GB (Sarin), and GA (Tabun). These chemicals present a significant toxic hazard because of their action on the nervous systems of humans and animals through inhibition of the acetyl-cholinesterase enzyme. They are both considered extremely toxic. VX is more acutely toxic than GB, but the latter represents a greater potential hazard because of its higher volatility (about the same as water) and, thus, the greater likelihood of its being inhaled. Chronic health effects and cancer from low-level exposures have not been associated with nerve agents or with chemically (and toxicologically) similar commercially available organic phosphorus insecticides (Leffingwell, 1993). Only short-term symptoms have been documented in individuals who survive exposure to nerve agents.

The mustards (designated H [nondistilled mustard], HD [distilled mustard], and HT [thickened mustard]) do not present significant acute lethal hazards. Their principal effect is severe blistering of the skin and mucous membranes. They have been implicated as being carcinogenic, however, and may present a cancer hazard to individuals exposed acutely (Leffingwell, 1993; IOM, 1993). The estimates for induced cancers from accidental agent exposures only consider mustard agents.

Chemical agents, after being fully dispersed, do not tend to persist in the environment because their relatively simple chemical structures tend to undergo hydrolysis in humid climates. However, in extremely dry desert climates, they can remain for a considerable period of time (U.S. Army, 1988).

The chemical agents in the U.S. stockpile are stored in a variety of containment systems, including bulk (ton) containers, rockets, projectiles, mines, bombs, cartridges, and spray tanks. Figure 1-1 summarizes the stockpile configuration as of 1996 for the eight continental U.S. sites by agent, munition, and containment system (OTA, 1992; NRC, 1996a).

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