Degradation and fate of mustard in soil as determined by 13C MAS NMR

The environmental fate of chemical warfare agents is a current concern, and the notorious persistency of mustard in soil is well-known. The current study utilizes C-13 MAS NMR as an in situ method to study the behavior of mustard, and the common simulants 2-chloroethyl methyl sulfide (CEMS) and 2-chloroethyl phenyl sulfide (CEPS), in a sandy loam soil. Spreading of these water-insoluble liquids and surface sorption on the dry soil particles is observable, as is the recoalescence of liquid droplets and/or hydrolysis in the presence of added water. The relative hydrolysis rates are in agreement with those observed in solution. GEMS, possessing the shortest aqueous half-life, hydrolyzes without droplet reformation. But mustard and CEPS, possessing much longer aqueous half-lives, do not substantially hydrolyze prior to droplet reformation. For mustard, this behavior is crucial to its longevity in soil. Hydrolysis of CEMS and CEPS in the sandy loam soil yields predominately their corresponding alcohols, with some ether formation for the latter. Mustard hydrolysis in the sandy loam soil results in the nearly exclusive formation of the branched sulfonium ion HOCH2CH2SCH2CH2S+(CH2CH2OH)(2) (CH-TG). A simple model based on droplet size is presented to explain the persistency of mustard in soil.