Adsorption and Degradation of Dimethyl Selenide in Soil

Abstract

Dimethyl selenide (DMSe) is an organic vapor that is formed naturally from inorganic selenium species in soil. The behavior of DMSe directly regulates the geochemical cycling of selenium in the environment. In this study, the two fundamental reactions of DMSe in soil, adsorption and degradation, were investigated in batch experiments using headspace analysis. Adsorption of DMSe is negligible between the temperature of 4 and 40 °C and is insensitive to organic amendments. Degradation of DMSe, measured by a first-order rate constant, varied with soil type and organic amendment and was dependent on temperature but independent of soil moisture content over the range of 10% (by weight) to saturation. Degradation proceeded rapidly in a Hanford sandy loam, with a half-life of only 9 h. This compares to 875 h in a Losthill clay loam. Addition of compost manure or gluten (a pure protein) to the Hanford soil greatly increased the persistence of DMSe, which implies that the microorganisms consuming DMSe preferred the carbon source contained in the organic amendments. Our results show that, with respect to selenium remediation by dissipation into the atmosphere, many environmental and soil factors can be optimized to increase the probability of its diffusive transport through a soil.