Mustard environmental conditions

Lewisite is an oily, colorless liquid that can appear amber to black in its impure form. It has the odor of geraniums. It is more volatile than the mustard agents. Lewisite in the air can cause damage to the eyes, skin, and airways by direct contact. Lewisite in water can lead to exposures from drinking the water or from skin contact, and lewisite-contaminated food can be ingested. Lewisite remains as a liquid under a wide range of environmental conditions, from below freezing to very hot temperatures. 

Under environmental conditions, CWAs (vesicant agents, sulfur mustard (H, HD and HT) and lewisite (L) nerve agents, GA, GB, GD and VX) can undergo multiple-degradation processes such as hydrolysis, oxidation, dehydration and photolysis. These baseline degradation reactions can vary in rate and completeness, depending upon reaction temperature and pH, as well as the presence of free radicals and catalysts. Knowledge of these baseline reaction parameters has formed the basis for many modern decontamination procedures. 

The extent of changes seen in the respiratory tract following exposure to sulphur mustard is dependent upon the duration of the exposure and the concentration of the agent in the inhaled air. Under warm environmental conditions, the respiratory effects of sulphur mustard vapour were observed to be increased. Data collected during World War I are often difficult to interpret because of the high incidence of superadded infection in cases coming to post-mortem examination. 

The intensity of exposure variable is partially affected by the physical state and properties of the toxicant. Heavier-than-air gases are particularly affected by environmental conditions for example, warm environments increase the vaporization of some substances (such as mustard), making inhalational toxicity more likely. Increased humidity increases particle size by hygroscopic effects. Increased particle size may decrease the respiratory exposure to a toxicant because larger particles may precipitate prior to inhalation, or they may be collected preferentially in the upper airways, which have better clearance mechanisms. 

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. 

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... 

In a sulfur mustard vapor environment, unprotected military personnel will be exposed simultaneously via the respiratory and percutaneous routes. Such a combined exposure has not yet been studied, but it would be interesting to see which route would be predominant. Obviously, the environmental conditions will have a profound influence on the relative importance of the two exposure routes. 

Among chemical warfare (CW) agents, the arsenicals do not exhibit high levels of acute toxicity. But because of the imperishability of arsenic as an elemental constituent of them, arsenicals jeopardize the environment in the long term. In comparison, mustard agents may in principle be degraded to non-toxic products by the action of environmental conditions such as exposure to water, elevated temperatures and events that disperse it into fine droplets or particles. 

In view of the diversity of chemical fillings in an even larger diversity of munitions, it seems obvious that many analytical studies and much research on the fates of arsenicals under environmental conditions (soil and ground water) should be carried out. Needed also are similar investigations with respect to the different types of mustard. ... 

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