Volatile selenium fluxes from selenium-contaminated sediments in an Australian coastal lake

Overflows from ash dams associated with the operation of coal-fired power stations in Lake Macquarie, NSW, Australia, have been a historical source of selenium to the lake. Although dissolved selenium concentrations have been marginally elevated, sediments are the major sink. Methylation of sedimentary selenium to volatile dimethylselenide (DMSe) is known to be a natural remediation process. Sediments from north of Wyee Bay and the Vales Point Power Station were the subject of field sampling and monitoring to determine the extent to which selenium is being lost to the atmosphere as DMSe. Flux estimates were obtained by trapping volatile selenium species using benthic domes, followed by analysis in the field using a fully automated cryogenic trapping system with atomic fluorescence detection. The detection limit of the system was 0.1ngL-1 for DMSe and 1ngL-1 for dimethyl diselenide (DMDSe). Measurements in both summer and late autumn-early winter showed a distinct seasonal difference, with a higher summer DMSe flux of 53±25ng Se m-2h-1 (±s.d.) compared with 8±5ng Se m-2h-1 in late autumn-early winter. No DMDSe was detected. These fluxes are similar to those measured in Europe and North America, and represent an annual loss of 1.3kg of selenium per year from the nearby lake area. Lake-wide this would represent a significant loss to the atmosphere.