Degradation kinetics of VX

Abstract

O-ethyl S-(2-diisopropylaminoethyl)phosphonothiolate (VX) is among the most toxic of chemical warfare agents. VX is an oily liquid that is relatively involatile and is slow to hydrolyze, and thus may persist for weeks or longer in the environment, creating long term contamination of the territory. Concern over prolonged risk from VX exposure is exacerbated because it poses a dermal contact hazard -lethal dose on bare skin is about 10 mg/70 kg and it is readily absorbed through the skin. Therefore, a detailed understanding of its volatilization behavior and degradation pathways and rates is necessary. Volatilization has not been considered to be an important depletion mechanism, however, recent studies have shown a significant fraction of VX may volatilize. VX degradation reactions and their rates have been difficult to measure in many environmental media. For this reason, VX persistence has generally been described in terms of half lives. In this review, rates of VX degradation are compared on the basis of pseudo-first order rate constants in order to provide a basis for assessing VX persistence in a given environment. An issue of concern is that one VX degradation pathway produces S-2-(diisopropylaminoethyl) methylphosphonothioic acid (known as EA2192), a degradation product that is almost as toxic as VX. Consequently degradation pathways and rates for EA2192 are also discussed.