Bioavailability of heavy metals using simultaneously extracted metal/acid volatile sulfide in the sediments of Lake Burragorang, NSW, Australia

Lake Burragorang in the south west of Sydney is one of the largest domestic water supply storages in the world, holding 2,057,000 million liters of water. The reservoir provides approximately 80% of water for a population of about 4 million people. To ensure that the best quality water is delivered to Sydney residents the sediment of Lake Burragorang was analyzed for heavy metals as the cause of contamination could be the resuspension of settled material during major inflow events. This study was aimed to evaluate the distribution of heavy metals and their speciation in sediments of Lake Burragorang to predict their bioavailability to the aquatic system. Sediment core samples from Lake Burragorang were subjected to speciation using simultaneously extracted metal (SEM) and acid volatile sulfide (AVS) ratio to determine the potential toxicity of sediments due to metals. The results showed that these SEMs at all stations were higher than AVS and their ratio was found greater than 1, which indicates that available AVS is not sufficient to bind with the extracted metals for Lake Burragorang sediments and possibly contained metals potentially bioavailable to benthic organisms, however, SEM/AVS ratio was high owing to relatively low AVS values compared to values reported in the literature for fresh water sediments and not due to high concentrations of metals. In the current study even though these investigated metals were bioavailable in the sediment their individual metal concentrations are not expected to be toxic to benthic organisms as all locations had SEM concentrations lower than their threshold effect level (TEL). However, the slight increase in SEM above TEL will be detrimental for aquatic system as available AVS in sediment of Lake Burragorang is not sufficient to bind with the extracted metals.