Accelerated volatilization rates of selenium from different soils

Selenium (Se), an element found naturally in a variety of soils, can accumu late in drainage water of lands under intensive irrigation, even reaching l evels that are toxic to mammals and birds. Volatilization of Se by soil mic roorganisms into dimethylselenide (DMSe) can be enhanced by certain soil am endments and, thus, be used as a soil remediation process. In an 8-wk labor atory study, five soils from California and one from Germany were spiked wi th (SeO32-)-Se-75 (22.3 mg/kg Se). Two amino acids (DL-homocysteine and L-m ethionine), a carbohydrate (pectin), and a protein (zein) were tested as so il amendments. Gaseous Se-75 emissions were trapped with activated carbon a nd measured in a gamma counter. Depending on soil type, the cumulative vola tilization from the control flasks varied between 1.2% and 9.0% of applied Se-75. Both zein and L-methionine strongly increased volatilization (max. 4 3% of Se-75 applied), whereas DL-homocysteine had a much smaller stimulatin g effect. Pectin showed a moderate effect, but enhanced Se volatilization r ates were sustained much longer when compared to the zein amendment. Volati lization rates of Se followed a simple first-order reaction. Gaseous Se emi ssion in the soils treated with L-methionine yielded an S-shaped curve, whi ch fit a growth-modified first-order rate model. Although zein and L-methio nine were the most favorable treatments enhancing Se volatilization, all si x soils responded differently to the soil amendments.