which forms ethyl methylphosphonic acid (EMPA) and 2-(diisopropylamino) ethane thiol (DESH), which are both relatively nontoxic (Kingery and Allen, 1995; Munro et al., 1999). Cleavage of the S-C bond is a less prevalent process, and it also produces relatively nontoxic products. Basic sites such as those found on concrete have been shown to greatly increase the rates of hydrolysis via P-S and S-C cleavage (Groenewold et al., 2002; Williams et al., 2005).
VX hydrolysis via P-O cleavage is a matter of concern because this furnishes S-[2-(diisopropylamino)ethyl] methylphosphonothioic acid and ethanol (Yang et al., 1990). The former product, known as EA-2192, retains much of the neurotoxicity of the intact agent, and hence presence of this compound is an ongoing source of concern. In fact, the state of Utah requires measurement of EA-2192 to ensure detoxification to closure standards (see Chapter 5). Concerns related to EA-2192 are reasonably mitigated, however, by the following considerations:
EA-2192 has no volatility and poses no inhalation hazard.
EA-2192 does not diffuse through the skin barrier.
Hydrolysis of the EA-2192 proceeds fairly rapidly, with a rate constant on the order of that of the parent compound (0.1 day–1) (Kaaijk and Frijlink, 1977; Verweij and Boter, 1976).
With regard to occluded spaces and permeable polymers, it should be noted that there may be potential for survival of intact VX sequestered in these environments. This may occur because VX thus sequestered may be protected from hydrolysis.
Bis-(2-chloroethyl)sulfide, or sulfur mustard, can refer to H, HD (distilled mustard), or HT (distilled mustard mixed with bis-(2-(2-chloroethylthio)ethyl) ether) in the context of this report. H is relatively involatile, with a vapor pressure of 9 × 10–2 mm Hg at 25ºC (Reutter, 1999). Thus H, in any form, would be expected to display some persistence.
Mustard is detoxified by hydrolysis, but in general, rates of mustard hydrolysis are slower than those of the nerve agents. Nevertheless, hydrolysis would be expected to result in depletion of mustard under most situations if enough time passes between the end of operations and demolition. Chemical decontamination will accelerate rates of hydrolysis.
The generally slower rates of hydrolysis and low volatility serve to make the compound susceptible to surviving for extended periods of time in occluded spaces. This phenomenon is exacerbated by H polymerization reactions that can form a “skin” (Yang et al., 1988) over the surface of intact mustard. The skin can protect the underlying agent from exposure to water and other naturally occurring hydrolysis reagents. Rupture of the skin during scabbling2 or other demolition activities could release mustard and result in a toxic exposure risk. In addition to occupying pores, mustard will also permeate many polymeric materials, and it can be released later either as a result of demolition activities or by heating the polymer.
Black, R., R. Clarke, R. Read, and M. Reid. 1994. Application of Gas Chromatography-Mass Spectrometry and Gas Chromatography-Tandem Mass Spectrometry to the Analysis of Chemical Warfare Samples, Found to Contain Residues of the Nerve Agent Sarin, Sulphur Mustard and Their Degradation Products. Journal of Chromatography A 662(2): 301-321.
Davisson, M., A. Love, A. Vance, and J. Reynolds. 2005. UCRL-TR-209748 Environmental Fate of Organophosphorus Compounds Related to Chemical Weapons. Livermore, CA: Lawrence Livermore National Laboratory.
Epstein J., J. Callahan, and V. Bauer. 1973. The Kinetics and Mechanisms of Hydrolysis of Phosphonothiolates in Dilute Aqueous Solutions. Phosphorus 4: 157-163.
Groenewold, G., J. Williams, A. Appelhans, G. Gresham, J. Olson, M. Jeffery, and B. Rowland. 2002. Hydrolysis of VX on Concrete: Rate of Degradation by Direct Surface Interrogation Using an Ion Trap Secondary Ion Mass Spectrometer. Environmental Science & Technology 36(22): 4790-4794.
Kaaijk, J., and C. Frijlink. 1977. Degradation of S-2-di-isopropylaminoethyl O-ethyl methylphosphonothioate in Soil. Sulphur-Containing Products. Pesticide Science 8(5): 510-514.
Kingery, A., and H. Allen. 1995. The Environmental Fate of Organophosphorus Nerve Agents: A Review. Toxicological & Environmental Chemistry 47(3): 155-184.
Love, A., A. Vance, J. Reynolds, and M. Davisson. 2004. Investigating the Affinities and Persistence of VX Nerve Agent in Environmental Matrices. Chemosphere 57(10): 1257-1264.
Munro, N., S. Talmage, G. Griffin, L. Waters, A. Watson, J. King, and V. Hauschild. 1999. The Sources, Fate, and Toxicity of Chemical Warfare Agent Degradation Products. Environmental Health Perspectives 107(12): 933-974.
Reutter, S. 1999. Hazards of Chemical Weapons Release during War: New Perspectives. Environmental Health Perspectives 107(12): 985-990.
Verweij, A., and H. Boter. 1976. Degradation of S-2-Di-isopropylaminoethyl O-ethyl Methylphosphonothioate in Soil: Phosphorus-Containing Products. Pesticide Science 7(4): 355-362.