Groenewold Gary S, Williams John M, Appelhans Anthony D, Gresham Garold L, Olson John E, Jeffery Mark T, Rowland Brad
Idaho National Engineering and Environmental Laboratory, Idaho Falls, Idaho 83415-2208, USA.
Environ Sci Technol. 2002 Nov 15;36(22):4790-4. doi: 10.1021/es025754n.
The nerve agent VX (O-ethyl S-2-diisopropylaminoethyl methylphosphonothiolate) is lethal at very low levels of exposure, which can occur by dermal contact with contaminated surfaces. Hence, behavior of VX in contact with common urban or industrial surfaces is a subject of acute interest. In the present study, VX was found to undergo complete degradation when in contact with concrete surfaces. The degradation was directly interrogated at submonolayer concentrations by periodically performing secondary ion mass spectrometry (SIMS) analyses after exposure of the concrete to VX. The abundance of the [VX + H]+ ion in the SIMS spectra was observed to decrease in an exponential fashion, consistent with first-order or pseudo-first-order behavior. This phenomenon enabled the rate constant to be determined at 0.005 min(-1) at 25 degrees C, which corresponds to a half-life of about 3 h on the concrete surface. The decrease in [VX + H]+ was accompanied by an increase in the abundance of the principal degradation product diisopropylaminoethanethiol (DESH), which arises by cleavage of the P-S bond. Degradation to form DESH is accompanied by the formation of ethyl methylphosphonic acid, which is observable only in the negative ion spectrum. A second degradation product was also implicated, which corresponded to a diisopropylvinylamine isomer (perhaps N,N-diisopropyl aziridinium) that arose via cleavage of the S-C bond. No evidence was observed for the formation of the toxic S-2-diisopropylaminoethyl methylphosphonothioic acid. The degradation rate constants were measured at four different temperatures (24-50 degrees C), which resulted in a linear Arrhenius relationship and an activation energy of 52 kJ mol(-1). This value agrees with previous values observed for VX hydrolysis in alkaline solutions, which suggests that the degradation of submonolayer VX is dominated by alkaline hydrolysis within the adventitious water film on the concrete surface.
神经性毒剂VX（O-乙基-S-2-二异丙氨基乙基甲基硫代膦酸酯）在极低暴露水平下就具有致命性，这种暴露可能通过皮肤接触受污染表面而发生。因此，VX与常见城市或工业表面接触时的行为是一个备受关注的问题。在本研究中，发现VX与混凝土表面接触时会完全降解。通过在混凝土暴露于VX后定期进行二次离子质谱（SIMS）分析，直接在亚单层浓度下研究了降解情况。观察到SIMS光谱中[VX + H]+离子的丰度呈指数下降，这与一级或准一级反应行为一致。这种现象使得在25℃下测定的速率常数为0.005 min⁻¹，这相当于在混凝土表面的半衰期约为3小时。[VX + H]+的减少伴随着主要降解产物二异丙氨基乙硫醇（DESH）丰度的增加，DESH是由P-S键断裂产生的。降解形成DESH的同时会生成乙基甲基膦酸，仅在负离子光谱中可观察到。还涉及到第二种降解产物，它对应于一种通过S-C键断裂产生的二异丙基乙烯胺异构体（可能是N,N-二异丙基氮丙啶）。未观察到有毒的S-2-二异丙氨基乙基甲基硫代膦酸形成的证据。在四个不同温度（24 - 50℃）下测量了降解速率常数，结果得到线性阿伦尼乌斯关系，活化能为52 kJ mol⁻¹。该值与先前在碱性溶液中观察到的VX水解值一致，这表明亚单层VX的降解主要由混凝土表面吸附水膜中的碱性水解主导。
