Accelerated volatilization rates of selenium from different soils

Selenium (Se), an element found naturally in a variety of soils, can accumulate in drainage water of lands under intensive irrigation, even reaching levels that are toxic to mammals and birds. Volatilization of Se by soil microorganisms into dimethylselenide (DMSe) can be enhanced by certain soil amendments and, thus, be used as a soil remediation process. In an 8-wk laboratory study, five soils from California and one from Germany were spiked with 75SeO3(2-) (22.3 mg/kg Se). Two amino acids (DL-homocysteine and L-methionine), a carbohydrate (pectin), and a protein (zein) were tested as soil amendments. Gaseous 75Se emissions were trapped with activated carbon and measured in a gamma counter. Depending on soil type, the cumulative volatilization from the control flasks varied between 1.2% and 9.0% of applied 75Se. Both zein and L-methionine strongly increased volatilization (max. 43% of 75Se applied), whereas DL-homocysteine had a much smaller stimulating effect. Pectin showed a moderate effect, but enhanced Se volatilization rates were sustained much longer when compared to the zein amendment. Volatilization rates of Se followed a simple first-order reaction. Gaseous Se emission in the soils treated with L-methionine yielded an S-shaped curve, which fit a growth-modified first-order rate model. Although zein and L-methionine were the most favorable treatments enhancing Se volatilization, all six soils responded differently to the soil amendments.