Effects of Carbon and Trace Element Addition on Alkylselenide Production by Soil

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Abstract
Microbial volatilization of selenium (Se) may be applicable for detoxifying Se‐contaminated soils, if high rates of volatilization can be maintained. This study was conducted to evaluate some of the factors affecting the rates of microbial production of alkylselenides. Field‐moist Los Baños clay loam, representing soils from Se‐affected areas, was treated with 100 mg kg−1 Se(IV), labeled with 75Se(IV). Gaseous Se was determined by direct gamma counting of activated charcoal traps. Without C amendments, the volatilization potential was 2.9% in 13 d; amendments with 2 g C(pectin) kg−1 soil increased that potential to 8.8%. With other C sources volatilization in 13 d was 6.6% [corn (Zea mays L.) leaves], 5.2% (starch), 3.7% (dairy manure), 3.3% (cellulose), and 2.7% (sewage sludge). Volatilization rates decreased as C was depleted, but increased again upon C reload. The addition of molybdenum (Mo), mercury (Hg), chromium (Cr), and lead (Pb) greatly inhibited Se volatilization, while arsenic (As), boron (B), and manganese (Mn) had little effect. The presence of cobalt (Co), zinc (Zn), and nickel (Ni) at relatively high levels (25 mmol kg−1) increased Se volatilization rates up to 2.5‐fold. After 37 d of incubation, recovery of added Se(IV) as alkylselenides was as high as 34, 30, and 23% with Co, Zn and Ni, respectively, applied along with C amendments. Zinc, Co, and Ni most likely serve as cofactors in the methylation reaction. Low levels of N in the presence of added C slightly enhanced alkylselenide production, while without C amendments, N had a slightly inhibitory effect.

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