Redox effects in selenium behaviour in estuarine porewaters

Selenium is an anthropogenic contaminant of concern in estuaries on the NSW coast. Experiments have been performed to elucidate the processes controlling selenium remobilisation from contaminated sediments. Measurements of redox potential and pH were made in sediments taken from Lake Macquarie with different populations of infaunal organisms. Depending on the feeding mechanisms and mobility of the organisms, bioturbation causes a degree of deepening of the oxidised conditions in the sediment. Thermodynamic simulations of the solubility of selenium in estuarine porewaters predict a mobilisation of the contaminant under such conditions. Preliminary experiments involving exposure of contaminated reduced sediment to oxidising porewater resulted in the mobilisation of selenium species that were strongly bound to the sediment

Bioturbation effects on selenium mobility

Bioturbation is a natural process with potential to affect the dynamics of contaminants in sedimentary environments. In this investigation, two benthic organisms, the bivalve mollusc Notospisula trigonella and the eunicid polychaete Marphysa sanguinea were maintained at different densities in selenium contaminated sediments. Porewater and bulk sediment selenium concentrations were determined over a 20 day period. The benthos in this experiment appeared to raise the porewater concentrations with respect to the controls. Both animals accumulated selenium from the sediment mesocosms. Toxic effects were observed in both animals

Dynamic Modelling of Selenium Biogeochemistry in an Estuarine Lake - Lake Macquarie, NSW

The mobility and toxicity of selenium (Se) is a strong function of oxidation state, which in turn is affected by Eh and pH. Elevated levels of Se in fish from Lake Macquarie, NSW are potentially linked to reported high levels of Se in the sediment. Therefore, an understanding of the biogeochemical cycling of Se between the various environmental compartments in the Lake is important in predicting the formation and release of mobile and potentially toxic Se oxyanions to the water column. A computer-based dynamic model, developed in SPEEDUP, is described. The model simulates the biogeochemical cycling of Se in an estuarine ecosystem between the sediment and the water column. Model parameters were obtained from the literature and from data specific to Lake Macquarie. Transport of Se between and accumulation of Se within the various compartments is predicted. Selenium is expected to accumulate in volatile, organic and selenate forms in the water column, and to predominate as selenide in the sediment. The model is designed to allow future expansion into different environmental compartments, including air, biota and plants

Selenium in sediment, pore water and benthic infauna of Lake Macquarie, New South Wales, Australia

Measurements of selenium in sediments and benthic infauna of Lake Macquarie, an estuary on the east coast of Australia, indicate that sediments are a significant source of selenium in the lake's food web. Analysis of surficial sediment samples indicated higher selenium con- concentrations near what are believed to be the main industrial sources of selenium to the lake: a smelter and a power station. Sediment cores taken from sediments in Mannering Bay, near a power station at Vales Point, contained an average of 12 times more selenium in surficial sections than sediment cores from Nord's Wharf, a part of the lake remote from direct inputs of selenium. The highest selenium concentration found in Mannering Bay sediments (17.2 mg/g) was 69 times the apparent background concentration at Nord's Wharf (0.25 mg/g). Pore water concentrations in Mannering Bay were also high, up to 5 mg/l compared to those at Nord's Wharf which were below detection limits (0.2 mg/l). Selenium concentrations in muscle tissues of three benthic-feeding fish species (Mugil cephalus, Platycephalus fuscus, Acanthopagrus australis) were significantly correlated ( p < 0:05) with surficial sediment selenium concentra- tion. Selenium concentrations in polychaetes and molluscs of Mannering Bay were up to 58 times higher than those from Nord's Wharf. Two benthic organisms, the eunicid polychaete Marphysa sanguinea and the bivalve mollusc Spisula trigonella, were maintained at different densities in selenium-spiked sediments. Both animals accumulated selenium from the spiked sediment, confirming that bioaccumulation from contaminated sediments occurs. Collectively, these data suggest that benthic food webs are important sources of selenium to the fish of Lake Macquarie