LONG-TERM DEPLETION OF SELENIUM FROM KESTERSON DEWATERED SEDIMENTS

Microbial methylation of selenium (Se) to volatile (CH3)(2)Se may cont ribute to a considerable loss of the Se inventory from seleniferous so ils over time. A field experiment was carried out to assess microbial volatilization of Se as a bioremediation approach to dissipate Se. Fie ld plots of size of 3.7 x 3.7 m(2) were established at the Kesterson R eservoir, California. To enhance microbial activity, the plots were tr eated with different C and protein amendments and were periodically ti lled and irrigated. Over a period of 100 months, 68-88% of the total a mount of Se dissipated from the topsoil (0-15 cm). The pattern of Se d epletion in soil was not correlated with rainfall events nor with temp erature. As most of the rainfall occurred during the cold winter month s, it is likely that leaching dominated the Se depletion in winter whe reas volatilization prevailed in summer. The highest amount of Se depl etion occurred with the amendment of the protein casein. However, ther e was no statistically significant difference in Se removal from the d ifferent treatments compared to the case where there was no C or prote in amendment. Tillage and irrigation presumably prevailed over the eff ects of the amendments. A two-compartment model was superior to a one- compartment model for describing the long-term kinetics of Se depletio n in soil. The rate of Se dissipation was initially faster than at lat er times. This indicates that the rate-limiting mechanisms have change d during the time of the study. (C) 1997 Elsevier Science B.V.