Long-term depletion of selenium from Kesterson dewatered sediments

Microbial methylation of selenium (Se) to volatile (CH3)2Se may contribute to a considerable loss of the Se inventory from seleniferous soils over time. A field experiment was carried out to assess microbial volatilization of Se as a bioremediation approach to dissipate Se. Field plots of size of 3.7 × 3.7 m2 were established at the Kesterson Reservoir, California. To enhance microbial activity, the plots were treated with different C and protein amendments and were periodically tilled and irrigated. Over a period of 100 months, 68–88% of the total amount of Se dissipated from the topsoil (0–15 cm). The pattern of Se depletion in soil was not correlated with rainfall events nor with temperature. As most of the rainfall occurred during the cold winter months, it is likely that leaching dominated the Se depletion in winter whereas volatilization prevailed in summer. The highest amount of Se depletion occurred with the amendment of the protein casein. However, there was no statistically significant difference in Se removal from the different treatments compared to the case where there was no C or protein amendment. Tillage and irrigation presumably prevailed over the effects of the amendments. A two-compartment model was superior to a one-compartment model for describing the long-term kinetics of Se depletion in soil. The rate of Se dissipation was initially faster than at later times. This indicates that the rate-limiting mechanisms have changed during the time of the study.