Fate of dimethyldiselenide in soil.

Volatilization of dimethyldiselenide (DMDSe) is one of the most important processes for removing selenium (Se) from Se-contaminated environments. However, the fate of DMDSe in soil is not known. In this study, we monitored the changes of DMDSe in the head space of soil samples spiked with known amounts of DMDSe gas, and fractionated and speciated the resulting Se forms in soil. Dimethyldiselenide was highly dissolved in water in a closed air-water system and was highly sorbed onto soil in a closed air-soil system. Chemical and biological transformations of DMDSe in soil converted a large amount of DMDSe to nonvolatile Se compounds. Elemental Se [Se(0)] and nonvolatile organic Se were the major forms of Se transformed from spiked DMDSe. Microbial conversion of DMDSe to dimethylselenide (DMSe) in soil increased the production of DMSe. Calculation of the mass recovery showed that about 85 to 93% of the added DMDSe was recovered as Se(0), organic Se, organic material Se (OM-Se), Se(IV), and volatile organic Se in the head space in the non-autoclaved soils and 50 to 70% of the added DMDSe was recovered in the autoclaved soils. These results indicate that DMDSe is not a stable form of Se, and it may be one of the important precursors of DMSe in the soil environment.