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, Au stralia has recently focussed attention on the environmental status of rive r catchments of the main reservoir, Lake Burragorang. Although the Coxs Riv er - a major catchment of Lake Burragorang - comprises mainly forests and g razing land, it supports a moderate sized town, power stations and coal min es. The heavy metal content of stream-bed sediments characterises environme ntal impact in this rural catchment and sources of contamination. Sediment in a creek flowing through a country town (population 12 000) is markedly e nriched in Cr, Pb and Zn (3x, 18x and 52x, respectively) over background, p robably due to a long history of metal-based industry. The highest Cu, Pb a nd Zn concentrations (204, 332 and 2460 mug 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 and 157 mug g(-1), resp ectively) to ambient fluvial sediments, possibly from cooling towers and co al storage areas. The highest Co and Cr concentrations (113 and 490 mug g(- 1)) in fluvial sediments of this catchment are associated with coal-mining activities. Selective extraction indicates that about 50% of the anthropoge nic fraction may be bioavailable, whereas sequential extraction procedures suggest that < 25% is associated with the easily exchangeable/adsorbed phas e. Two dams restrict the migration of heavy metals down the Coxs River and sediment discharging into Lake Burragorang is low in metals.