VX Evaporation and Degradation from Urban Land Surfaces

Abstract

Evaporation and degradation of the nerve agent, VX [O-ethyl S-2-(N,N-diisopropylamino)ethyl methylphosphonothioate] was explored on common urban or industrial surfaces, including sand, soil, and concrete. Concentration profiles of VX vapor were obtained using a laboratory-sized wind tunnel and thermal desorber in conjunction with gas chromatography. Results show that released VX vapors amounted to <20% of the applied mass and evaporation rates were found to be 0.12 μg/min in sand, 0.088 μg/min in soil, 0.16 μg/min in concrete (water–cement ratio, w/c = 0.50), which are ∼5–10 times slower than in the glass surface. At elevated temperature of 35°C, rates remarkably increased at 0.44 μg/min in sand, 0.12 μg/min in soil, and 0.67 μg/min in concrete. Rates also increased with lower w/c in concrete (0.48 μg/min in concrete [w/c = 0.42] and 0.76 μg/min in concrete [w/c = 0.31]). On the other hand, a drop of neat VX sorbed into the matrices remained for days and degraded following a pseudo first-order rate reaction. Estimated half-lives of VX in these matrices were ∼6 days in sand, 8 days in soil, and 3 days in concrete (w/c = 0.50) at room temperature. Degradation products were the following: ethyl methylphosphonic acid (EMPA), ethyl methylphosphonothioic acid (EMPT), methylphosphonic acid (MPA), 2-(diisopropylamino)ethanethiol (DESH), and bis(2-diisopropylaminoethyl) sulfide [(DES)2]. Parameters, which were quantified and evaluated in this study, will be useful for database establishment in risk assessment of exposure of the general population to highly lethal VX.