Lewisite persistence

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. 

There are seven sites in the United States where U.S. Unitary Chemical Stockpile exists. Below they are listed by chemical weapon as follows GB, sarin H, mustard HD, mustard HT, mustard VX, persistent nerve agent GA, tabun L, lewisite TGA, thickened tabun TGB, thickened sarin. 

Blister agents such as distilled mustard (HD) and nitrogen mustard (HN) have a slow rate of action and might be persistence for three days to one week in warm weather and for some weeks in cold weather, while lewisite (L) and mustard/lewisite (HL) have a quick rate of action and would be persistent for one to three days during summer and for weeks during winter. Route of entry for these blister agents would be nearly the same eyes, lungs, and skin for vapor or aerosol, but for liquid, the points of entry would be the eyes and skin for HD and HN and eyes, skin, and mouth for L and HL. 

Lewisite (L, 2Cchloroviny Idichloroarsine, 2-chlorovinyl arsonous dichloride) Vesicant — blister agent with Arsenic 30-50 mg/Kg (skin) Highly persistent because of Arsenic in formulation... 

Liquid lewisite applied by eye-dropper to the forearms of men caused blanching and discoloration of the skin followed by extensive erythema within 15 to 30 minutes and vesication within 12 hours or less (Wardell, 1941, as cited in Goldman and Dacre, 1989). The pain associated with these dermal exposures reportedly occurred within two minutes and considerable discomfort persisted for about one week. Other tests with human subjects and clinical reports also indicate a similar temporal sequence of events. Exposure to lewisite vapor (0.06 to 0.33 mg/L) caused discoloration and blistering with the maximum effect occurring by 36 to 48 hours after exposure (Wardell, 1941). At a concentration of 0.01 mg/L, lewisite vapor caused inflammation of the eyes and swelling of the eyelids after 15 minutes of exposure, and inhalation of 0.5 mg/L for five minutes is considered to be potentially lethal. 

Lewisite in soil may rapidly volatilize or may be converted to lewisite oxide due to moisture in the soil (Rosenblatt et al, 1975). The low water solubility suggests intermediate persistence in moist soil (Watson and Griffin, 1992). Both lewisite and lewisite oxide may be slowly oxidized to 2-chlorovinylarsonic acid (Rosenblatt et al, 1975). Possible pathways of microbial degradation in soil include epoxidation of the C=C bond and reductive deha-logenation and dehydrohalogenation (Morrill et al, 1985). Due to the epoxy bond and arsine group, toxic metabolites may result. Additionally, residual hydrolysis may result in arsenic compounds. Lewisite is not likely to bioaccumulate. However, the arsenic degradation products may bioaccumulate (Rosenblatt et al, 1975). 

CWAs have been widely eondemned since they were first used on a massive scale during World War I. However, they are still stockpiled and used in many countries as they are cheap and relatively easy to produee, and can cause mass casualties. Although the blood agent CK is extremely volatile and undergoes rapid hydrolysis, the degradation of three types of vesicant CWAs, the sulfur mustards, nitrogen mustards, and Lewisite, results in persistent products. For... 

One day I was taken for a jeep ride over the testing field. We passed a twisted metal object with liquid in its concave portion. The soldier driver steered clear of it and said it was the remains of an air-drop bomb and the liquid was residual war gas. It was December and quite cold. The laboratory crew told me about a big experiment Dugway had recently performed. The Army shaved the wool off the backs of a flock of sheep, and in an area remote firom the headquarters built a fence to contain the sheep. Aircraft flew overhead at an unspecified elevation and sprayed a large amount of Lewisite (one of the World War I persistent gases). The sheep were examined but showed no damage. Apparently, the Lewisite evaporated before reaching the ground. 

However, Nielson s work shows that these data have only an approximate value and indicate merely the order of magnitude of the persistence. Nielson observed, inter alia, that in Leitner s formula the time of evaporation of a substance is compared with that of water into a dry atmosphere, whereas in practice the atmosphere always contains a certain amount of water which retards the velocity of evaporation. Nevertheless, the data for persistence obtained from Leitner s formula, though they have only an approximate value, are of interest from the practical point of view, for they allow values of the persistences of different gases to be compared. For example, from Table XI it is seen that the relative persistences of dichloroethyl sulphide and lewisite at 25° C. are as 44 is to 6-9, and this signifies that at this temperature dichloroethyl sulphide is about six times as persistent as lewisite. 

The reactions with thiol groups (e.g., those that are found in proteins) form an alkylarsine sulfide. Mustard gas, at the same LCtso, induces vesication, whereas Lewisite does not. Apparently, Lewisite is more irritating initially to the pulmonary systems than mustard. The hydrolysis products are more persistent in soil in comparison with mustard. In ambient air. Lewisite is about 10 times more volatile than mustard. 

Pure Lewisite is an oily, colorless liquid, and impure Lewisite is amber to black in color. It has a characteristic odor of geraniums. Lewisite is much more volatile and persistent in colder climates than mustard. Lewisite remains fluid at lower temperatures, which makes it perfect for winter dispersal. Lewisite hydrolyzes rapidly, and, on a humid day, maintaining a biologically active concentration of vapor may be difficult (U.S. Department of Defense, 1990). 

There are no data on human exposure from which to predict the long-term effects from Lewisite. There is no substantial evidence to suggest that Lewisite is carcinogenic, teratogenic, or mutagenic (Goldman and Dacre, 1989). The committee appointed by the National Academy of Science reported a causal relationship between Lewisite exposure and chronic respiratory diseases, and also that acute, severe injuries to the eye from Lewisite will persist (Pechura and RaU, 1993). 

CW agents may also be encountered as mixtures or solutions of one agent in another, or of an agent in a solvent. The mixing of lewisite with sulphur mustard has been undertaken to lower the vapour pressure and freezing point of the mustard and hence to increase its persistence, without reducing the effective CW payload of weapon systems. Sulphur mustard has also been mixed with phenyldichlorarsine, the mixture being referred to as Winterlost, i.e. winter mustard. 

Fig. 4-2. Agent vaporization increases in proportion to energy sources such as heat from explosive charges or from ambient heat (as measured by air or surface temperatures). Vapor persistence is then determined by weather factors such as wind and humidity. Hydrolysis rates are affected by factors such as temperature and solubility. Agents show characteristic hydrolysis rates in water, and water vapor, as described by humidity, may cause significant hydrolysis of vaporized agent. The vesicant Lewisite, for example, shows relatively rapid hydrolysis in water vapor, while the nerve agent VX is more resistant to hydrolysis.

Formulation is also used to manipulate the fate of the agent. Soman, VX, Lewisite, and sulfur mustard can be mixed with high-molecular-weight thickeners to increase droplet size and thereby decrease primary vaporization. Such additives are generally used to promote efficient agent deposition on the target site. Thickeners can also increase agent persistence and may hamper decontamination efforts. 

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