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THE U.S. CHEMICAL WEAPONS STOCKPILE 41 sulfur-containing impurities. HD, which is a distilled form of H, consists of nearly pure mustard. HT is a mixture of 60 percent HD with 40 percent other sulfur and chlorine compounds. I-IT is similar in appearance and biological activity to H and HD but is somewhat more active biologically. There is also the blister agent Lewisite (L), an arsenic compound, which is stored in only small amounts in the U.S. stockpile. Mustard has a garlic-like odor, with significant volatility at ordinary temperatures. It thus presents both vapor and contact hazards. Because mustard is nearly insoluble in water, it is very persistent in the environment and can contaminate soils and surfaces for long periods of time. All the chemical agents above are soluble in organic solvents; GB is also very soluble in water and VX is somewhat soluble. None of these chemical agents exists in pure form in either munitions or bulk containers. In munitions, GB and VX are stabilized with various compounds to prevent acid formation and decomposition of the agent. 4 Various impurities present at the time of manufacture and products of polymerization and decomposition (aging) are also present in the stockpiled agents. During Operational Verification Testing (OVT) at the Johnston Island storage site, for example, mustard agent was frequently been found in gel as well as liquid form. Toxicity of the Agents Nerve agents are the most lethal of the chemical warfare agents. VX is more toxic than GB, which is more toxic than GA. The peripheral nervous system of the human body uses either norepinephrine or acetylcholene (ACh) for neurotransrnission. The neurons of the sympathetic nervous system release norepinephrine to carry the final impulse to the end organs. Those of the parasympathetic system release acetylcholine. Acetylcholine also plays a vital role in the control of skeletal muscles autonomic ganglia and many structures within the central nervous system. The lethal effects of nerve agents result principally from inhibiting and inactivating of acetylcholinesterase (ACHE), an enzyme responsible for the normal breakdown of ACh.5 This inhibition results in the failure of the 4 For example, diisopropyl carbodiimide is used as a stabilizer for GB and VX and tributylamine is used as a stabilizer for GB. Trace metals such as nickel, copper, aluminum, and iron can also be found in stored agents. HD is often thickened by the addition of 5 to 10 percent polymer (Yang et al., 1992). 5 Once inside the body, VX not only inhibits AChE but also reacts directly with ACh receptors and other neurotransmitter receptors. The high toxicity of VX is also attributable to its high specificity for, and thus inhibition of, AChE.
