Fate of Chemical Warfare Agents on Soil: GD and VX

We investigated individually the fates of the organophosphorous nerve agents GD [methylphosphonofluoridic acid 1,2,2-trimethylpropyl ester] and VX [O-ethyl S-(2-diisopropylaminoethyl) methylthiolphosphonoate]. We developed methods for determining the fate of chemical warfare agents delivered as droplets onto soil, using Soil System Units to investigate agent persistence and potential for displacement into the atmosphere resulting from soil moisture (rainfall). We sampled the air above the soil surface, monitoring agent evaporation plus displacement into atmosphere occurring from the application of simulated rainfall. VX was minimally displaced by rainfall, compared to GD which was displaced to potentially hazardous atmospheric levels. We also investigated agent extractability from soil as a function of contact time. Duration of agent contact with soil significantly (p<0.05) affected recoveries of VX or GD from sands and humus, with recoveries ranging from 94-0.4% at t=0, to 24-0.06% after 72 hours of contact; with extremely low and relatively-constant recoveries from clay. Although the vast majority of VX and GD remained residual in soil after rainfall events, these may pose a potential contact hazard. We are currently developing methods for assessing the potential contact hazard at sand surfaces by applying a malleable transfer material to evaluate both effective surface concentrations and the potential for contact transfer.