Fate of dimethylsilanediol (DMSD) in outdoor bare surface soil and its relation to soil water loss

Dimethylsilanediol (DMSD) is a primary degradation product of silicone materials in the environment. Due to its low air/water partition coefficient and low soil/water distribution coefficient, this compound is not expected to undergo sorption and volatilization in wet soil. In an accompanying paper, we confirm that under controlled indoor conditions in test tubes, there is little to no volatilization of DMSD from soil and soil constituents if soil is wet. However, a significant amount of DMSD was volatilized when the soil substrates became air dried. Given the importance of water on the partition and fate of DMSD, we now report a continuation of this study focusing on the relation between DMSD removal and water loss in re-constituted soil columns under outdoor conditions. Consistent with predictions based on its partition properties and reconciling this evidence with previously reported field and laboratory studies, DMSD distribution was found to be largely dependent on water partitioning. The results suggested that DMSD moved upward in soil profile as soil water was evaporated from topmost layers with little DMSD retention by the soil matrix. As soil dried, a fraction of DMSD was sorbed by the soil matrix in the topmost layer, while most of the spiked radio-labeled DMSD was removed from soil through volatilization.