Mustard environmental persistence

Nitrogen mustards have not been stockpiled in most countries and are not further discussed here other than to say that their chemical properties resemble those of sulfur mustard (IOM, 1993). The toxicity and environmental fate of the nitrogen mustard agents have been reviewed previously (Marrs et al., 1996 Munro et al., 1999). Based on chemical properties, the persistence of nitrogen mustards range from environmentally persistent (tris[2-chloroethyl] amine... 

Sulfur mustard can be considered environmentally persistent because it is chemically stable and of low volatility. When protected from weathering conditions, it may persist in soil for years. VX is moderately persistent because of low volatility and slow rate of hydrolysis. The G-agents can be considered non-persistent on the basis of volatility and hydrolysis rates. Depending on environmental conditions, their half-lives may be measured in hours to days. Lewisite is rapidly hydrolyzed but the insoluble oxide formed is stable in the environment. In addition, arsenical degradation products of lewisite persist in the environment. Because of its extreme volatility and relatively rapid hydrolysis, cyanogen chloride is not persistent in the environment. 

Although two of the nitrogen mustards are not specifically treated in this review, their chemical properties resemble those of sulfur mustard and their fate in the environment is briefly discussed. Based on chemical and physical properties, HN3 [(CH2CH2C1)3N] can be considered environmentally persistent and HNl [(CH2CH2C1)2NC2H5) and HN2 [(CH2CH2Cl)2NCH3l can be considered moderately persistent. 

The agents that can be considered environmentally persistent, in varying degrees, are VX, sulfur mustard, and lewisite. Agent VX exhibits very low volatility and a slow rate of hydrolysis its half-life in soil may be measured in weeks to months, depending on environmental conditions. Sulfur mustard may persist... 

Once chemical agents are fully dispersed, they do not tend to persist in the environment because of their high chemical reactivity, particularly with water (hydrolysis). However, in extremely dry desert climates, they can persist for considerable periods of time (U.S. Army, 1988). The major environmental degradation products of nerve and mustard agents have recently been assessed and their persistence and toxicity evaluated. A potential hydrolysis product of VX (S-(2-diisopropylaminoethyl) methylphosphonothioic acid [EA-2192]) is a degradation product expected to display a high level of mammalian toxicity. Some mustard partial hydrolysis products are also toxic (Munro et al., 1999). 

Sulfur mustard is environmentally stable. After aerosolization by bomb explosion, shell blast or spraying, sulfur mustard vaporizes slowly, persisting in the environment for over a week in temperate climates (2). 

The primary environmental fate mechanism followed by stored or buried HD is hydrolysis. Although HD is rapidly hydrolyzed (a half-life of 4 to 8 min at 25° C in distilled water has been reported [Bartlett and Swain, 1949]), the overall process of hydrolytic destruction is limited by the very low water solubility of HD. Intermediate hydrolysis products and/or water-insoluble thickeners that can coat or encapsulate droplets of mustard retard hydrolysis. Because of low water solubility and formation of intermediate products, bulk amounts of HD may persist undispersed under water for some time. However, HD dispersed as droplets or mist, as in the case of an aerial attack, is expected to hydrolyze rapidly in humid air. 

Lewisite, CHCl=CHAsCl2, 2-chlorovinyldichloroarsine, named after its discoverer W. L. Lewis, was produced by the USA and shipped to Europe in 1918, too late to be used in WWI. Between the wars it was also produced by Japan and the Soviet Union. It is relatively easily made from arsenic trichloride and acetylene, although the process is technically more difficult than the production of sulfur mustard. Lewisite is more volatile (bp 190 °C) than sulfur mustard and hence it is less persistent it also appears to be more sensitive to environmental moisture. In contrast to sulfur mustard, its initial effect (skin pain or irritation) is almost instant, and blisters appear within a few hours. There has been no confirmed instance of use, although Japan is suspected of having used lewisite in China in WWII. In addition to being stockpiled as a neat agent, lewisite was mixed with sulfur mustard to speed up the onset of action and to depress the freezing point of the latter. 

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