VX

CAS RN:50782-69-9

Soil Adsorption / Mobility

Using a structure estimation method based on molecular connectivity indices(1), the Koc of VX can be estimated to be 187(SRC). According to a classification scheme(2), this estimated Koc value suggests that VX is expected to have moderate mobility in soil. The pKa of VX is 9.12(3) indicating that this compound will partially exist in the cation form in the environment and cations generally adsorb more strongly to soils containing organic carbon and clay than their neutral counterparts(4). Low concentrations of VX are tightly bound to dry Dugway soil(5). VX deposited on sand undergoes rapid adsorption followed by slow evaporation(6); adsorption to the sand can remain, but simulated rainfall can desorb the VX resulting in vapor-phase release(6). No VX sorption was observed with kaolinite, but VX sorption by montmorillonite was rapid with the predominant mechanism consistent with an ion exchange(7); VX also interacted with two soils resulting in sorption(7). A study compared the adsorption affinity of VX for several different surfaces similar to those found in the environment; activated charcoal, montmorillonite, and goethite(8). The activated charcoal had the greatest affinity, montmorillonite had a moderate affinity, and goethite had little affinity(8). Goethite's affinity increased with the addition of fulvic acid, but montmorillonite's did not(8). Although goethite degraded VX dissolved in methylene chloride, wet goethite was observed to block electron interactions and reduce degradation in soil(8).
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