The source of anthropogenic heavy metals in fluvial sediments of a rural catchment : Coxs River, Australia

A serious health scare involving the supply of drinking water to Sydney, Australia has recently focussed attention on the environmental status of river catchments of the main reservoir, Lake Burragorang. Although the Coxs River – a major catchment of Lake Burragorang – comprises mainly forests and grazing land, it supports a moderate sized town, power stations and coal mines. The heavy metal content of stream-bed sediments characterises environmental impact in this rural catchment and sources of contamination. Sediment in a creek flowing through a country town (population 12 000) is markedly enriched in Cr, Pb and Zn (3×, 18×and 52×, respectively) over background, probably due to a long history of metal-based industry. The highestCu, Pb and Zn concentrations (204, 332 and2460 g g-1, respectively) in fluvial sediment in the town are, however associated with discharges from a sewage treatment plant. Two coal-based power stations in the catchment contribute considerable Cu and Ni (maximum concentrations 562 and157 g g-1, respectively) to ambient fluvial sediments, possibly from cooling towers and coal storage areas. The highest Co and Cr concentrations(113 and 490 g g-1) in fluvial sediments of this catchment are associated with coal-mining activities. Selective extraction indicates that about 50% of the anthropogenic fraction may be bioavailable, whereas sequential extraction procedures suggest that <25% is associated with the easily exchangeable/adsorbed phase.Two dams restrict the migration of heavy metals down the Coxs River and sediment discharging into Lake Burragorang is low in metals.