Appendix C
Discussion of Hydrolysis Reactions of GB, VX, and H

The risk posed by agents depends upon their tendency to partition to phases where exposure could occur and on their stability and the toxicity of their degradation by-products. Thus, consideration of the physical and chemical properties of the agents provides a basis for evaluation of the potential risks of residual contamination. The risk associated with agents can be prolonged if they are sequestered in occluded spaces, and this tendency is also related to agent physical properties. Therefore, a brief review of the volatilization and hydrolysis reactivity of GB (sarin), VX, and mustard (H) are provided in the following paragraphs.

PROPERTIES OF GB (SARIN)

Although all three agents are considered semivolatile liquids, GB has a markedly higher vapor pressure (2.9 mm Hg at 25ºC) and will volatilize, leading to the conclusion that any residual GB would have been depleted by volatilization by the time facility destruction occurs (Reutter, 1999). Under normal environmental conditions, it also undergoes rapid hydrolysis, forming non-toxic products isopropyl methylphosphonic acid and fluoride (Kingery and Allen, 1995). GB can permeate into polymeric or porous materials, and there has been a report of unhydrolyzed GB in paint in an Iraqi shell fragment several years after exposure to the atmosphere (Black et al., 1994). The small residual levels of GB detected in this example suggest, however, that the potential exposure to residual GB after permeation into a polymeric or porous surface is likely minimal. In soil samples collected during the same Iraqi sampling campaign, intact GB was not detected (Black et al., 1994). Because GB is volatile and diffuses fairly rapidly, materials containing occluded spaces would be expected to release GB during the years between exposure and demolition. On the basis of these considerations, GB is considered to be a relatively nonpersistent agent.

PROPERTIES OF VX

VX has a much lower vapor pressure compared to GB (only 7 × 104 mm Hg at 25ºC) (Reutter, 1999), and exhaustive depletion due to volatilization from occluded spaces in porous or permeable surfaces may not occur. In situations where VX fills cracks or diffuses into permeable materials, volatilization will be inhibited, but subsequent disturbances of the system could expose intact VX, resulting in a potential exposure scenario resulting from volatilization or more likely from direct dermal contact.

For the most part, hydrolysis of VX results in detoxification. VX can be detoxified rapidly (rate constant on the order of 0.1 day–1) via hydrolysis reactions; however, not all hydrolysis reactions detoxify VX (Davisson et al., 2005; Love et al., 2004).1 The compound undergoes hydrolytic degradation via three pathways, involving cleavage of the P-S, S-C, and P-O bonds (Epstein et al., 1973; Munro et al., 1999). The principal pathway is cleavage of the P-S bond,

1

Rate studies of degradation of EA-2192 are few, and rates will certainly vary depending on the specific temperature, moisture present, and the surface with which the compound is in contact.



The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement



Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.

OCR for page 84
appendix c discussion of hydrolysis reactions of gB, vx, and h The risk posed by agents depends upon their ten- paign, intact GB was not detected (Black et al., 1994). dency to partition to phases where exposure could Because GB is volatile and diffuses fairly rapidly, mate- occur and on their stability and the toxicity of their rials containing occluded spaces would be expected degradation by-products. Thus, consideration of the to release GB during the years between exposure and physical and chemical properties of the agents provides demolition. On the basis of these considerations, GB is a basis for evaluation of the potential risks of residual considered to be a relatively nonpersistent agent. contamination. The risk associated with agents can be prolonged if they are sequestered in occluded spaces, ProPerTies oF vx and this tendency is also related to agent physical prop- erties. Therefore, a brief review of the volatilization and Vx has a much lower vapor pressure compared to GB (only 7 × 10–4 mm Hg at 25oC) (Reutter, 1999), hydrolysis reactivity of GB (sarin), Vx, and mustard (H) are provided in the following paragraphs. and exhaustive depletion due to volatilization from occluded spaces in porous or permeable surfaces may not occur. In situations where Vx fills cracks or dif- ProPerTies oF gB (sariN) fuses into permeable materials, volatilization will be Although all three agents are considered semivolatile inhibited, but subsequent disturbances of the system liquids, GB has a markedly higher vapor pressure (2.9 could expose intact Vx, resulting in a potential expo- mm Hg at 25oC) and will volatilize, leading to the con- sure scenario resulting from volatilization or more clusion that any residual GB would have been depleted likely from direct dermal contact. by volatilization by the time facility destruction occurs For the most part, hydrolysis of Vx results in (Reutter, 1999). Under normal environmental condi- detoxification. Vx can be detoxified rapidly (rate constant on the order of 0.1 day–1) via hydrolysis reac- tions, it also undergoes rapid hydrolysis, forming non- toxic products isopropyl methylphosphonic acid and tions; however, not all hydrolysis reactions detoxify Vx (Davisson et al., 2005; Love et al., 2004).1 The fluoride (Kingery and Allen, 1995). GB can permeate into polymeric or porous materials, and there has been compound undergoes hydrolytic degradation via three a report of unhydrolyzed GB in paint in an Iraqi shell pathways, involving cleavage of the P-S, S-C, and fragment several years after exposure to the atmosphere P-O bonds (Epstein et al., 1973; Munro et al., 1999). (Black et al., 1994). The small residual levels of GB The principal pathway is cleavage of the P-S bond, detected in this example suggest, however, that the potential exposure to residual GB after permeation into 1 Rate studies of degradation of EA-2192 are few, and rates will a polymeric or porous surface is likely minimal. In soil certainly vary depending on the specific temperature, moisture pres- samples collected during the same Iraqi sampling cam- ent, and the surface with which the compound is in contact. 

OCR for page 84
 APPENDIX C which forms ethyl methylphosphonic acid (EMPA) operations and demolition. Chemical decontamination and 2-(diisopropylamino) ethane thiol (DESH), which will accelerate rates of hydrolysis. are both relatively nontoxic (Kingery and Allen, 1995; The generally slower rates of hydrolysis and low Munro et al., 1999). Cleavage of the S-C bond is a volatility serve to make the compound susceptible to less prevalent process, and it also produces relatively surviving for extended periods of time in occluded nontoxic products. Basic sites such as those found on spaces. This phenomenon is exacerbated by H poly- concrete have been shown to greatly increase the rates merization reactions that can form a “skin” (yang et of hydrolysis via P-S and S-C cleavage (Groenewold al., 1988) over the surface of intact mustard. The skin et al., 2002; Williams et al., 2005). can protect the underlying agent from exposure to water Vx hydrolysis via P-O cleavage is a matter of concern and other naturally occurring hydrolysis reagents. Rup- ture of the skin during scabbling2 or other demolition because this furnishes S-[2-(diisopropylamino)ethyl] methylphosphonothioic acid and ethanol (yang et activities could release mustard and result in a toxic al., 1990). The former product, known as EA-2192, exposure risk. In addition to occupying pores, mustard retains much of the neurotoxicity of the intact agent, will also permeate many polymeric materials, and it and hence presence of this compound is an ongoing can be released later either as a result of demolition source of concern. In fact, the state of Utah requires activities or by heating the polymer. measurement of EA-2192 to ensure detoxification to closure standards (see Chapter 5). Concerns related reFereNces to EA-2192 are reasonably mitigated, however, by the Black, R., R. Clarke, R. Read, and M. Reid. 1994. Application of Gas following considerations: Chromatography-Mass Spectrometry and Gas Chromatography-Tan - dem Mass Spectrometry to the Analysis of Chemical Warfare Samples, • EA-2192 has no volatility and poses no inhalation Found to Contain Residues of the Nerve Agent Sarin, Sulphur Mustard hazard. and Their Degradation Products. Journal of Chromatography A 662(2): 301-321. • EA-2192 does not diffuse through the skin Davisson, M., A. Love, A. Vance, and J. Reynolds. 2005. UCRL-TR- barrier. 209748 Environmental Fate of Organophosphorus Compounds Related • Hydrolysis of the EA-2192 proceeds fairly rap- to Chemical Weapons. Livermore, CA: Lawrence Livermore National Laboratory. idly, with a rate constant on the order of that of the Epstein J., J. Callahan, and V. Bauer. 1973. The Kinetics and Mechanisms parent compound (0.1 day–1) (Kaaijk and Frijlink, of Hydrolysis of Phosphonothiolates in Dilute Aqueous Solutions. 1977; Verweij and Boter, 1976). 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 With regard to occluded spaces and permeable poly- of Degradation by Direct Surface Interrogation Using an Ion Trap Sec- mers, it should be noted that there may be potential ondary Ion Mass Spectrometer. Environmental Science & Technology for survival of intact Vx sequestered in these environ- 36(22): 4790-4794. Kaaijk, J., and C. Frijlink. 1977. Degradation of S-2-di-isopropylaminoethyl ments. This may occur because Vx thus sequestered O-ethyl methylphosphonothioate in Soil. Sulphur-Containing Products. may be protected from hydrolysis. Pesticide Science 8(5): 510-514. Kingery, A., and H. Allen. 1995. The Environmental Fate of Organo - phosphorus Nerve Agents: A Review. Toxicological & Environmental ProPerTies oF h (musTard ageNT) Chemistry 47(3): 155-184. Love, A., A. Vance, J. Reynolds, and M. Davisson. 2004. Investigating the Bis-(2-chloroethyl)sulfide, or sulfur mustard, can Affinities and Persistence of Vx Nerve Agent in Environmental Matri- ces. Chemosphere 57(10): 1257-1264. refer to H, HD (distilled mustard), or HT (distilled Munro, N., S. Talmage, G. Griffin, L. Waters, A. Watson, J. King, and V. mustard mixed with bis-(2-(2-chloroethylthio)ethyl) Hauschild. 1999. The Sources, Fate, and Toxicity of Chemical War- ether) in the context of this report. H is relatively fare Agent Degradation Products. Environmental Health Perspectives involatile, with a vapor pressure of 9 × 10–2 mm Hg at 107(12): 933-974. Reutter, S. 1999. Hazards of Chemical Weapons Release during War: New 25oC (Reutter, 1999). Thus H, in any form, would be Perspectives. Environmental Health Perspectives 107(12): 985-990. expected to display some persistence. Verweij, A., and H. Boter. 1976. Degradation of S-2-Di-isopropylamino - Mustard is detoxified by hydrolysis, but in general, ethyl O-ethyl Methylphosphonothioate in Soil: Phosphorus-Containing Products. Pesticide Science 7(4): 355-362. 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 2 Scabbling is a scarification process used to remove concrete situations if enough time passes between the end of surfaces.

OCR for page 84
 REVIEW OF CLOSURE PLANS FOR THE BASELINE INCINERATION CHEMICAL AGENT DISPOSAL FACILITIES Williams, J., B. Rowland, M. Jeffery, G. Groenewold, A. Appelhans, G. yang, y.-C., L. Szafraniec, W. Beaudry, and J. Ward. 1988. Kinetics and Gresham, and J. Olson. 2005. Degradation Kinetics of Vx on Concrete Mechanism of the Hydrolysis of 2-chloroethyl Sulfides. Journal of by Secondary Ion Mass Spectrometry. Langmuir 21(6): 2386-2390. Organic Chemistry 53(14): 3293-3297. yang, y.-C., L. Szafraniec, W. Beaudry, and D. Rohrbaugh. 1990. Oxidative Detoxification of Phosphonothiolates. Journal of the American Chemi- cal Society 112(18): 6621-6627.