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

Abstract

A serious health scare involving thesupply of drinking water to Sydney, Australia hasrecently focussed attention on the environmentalstatus of river catchments of the main reservoir, LakeBurragorang. Although the Coxs River – a majorcatchment of Lake Burragorang – comprises mainlyforests and grazing land, it supports a moderate sizedtown, power stations and coal mines. The heavy metal content of stream-bed sedimentscharacterises environmental impact in this ruralcatchment and sources of contamination. Sediment in acreek flowing through a country town (population 12 000) is markedly enriched in Cr, Pb and Zn (3×, 18×and 52×, respectively) over background, probably dueto a long history of metal-based industry. The highestCu, Pb and Zn concentrations (204, 332 and2460 μg g-1, respectively) in fluvialsediment in the town are, however associated withdischarges from a sewage treatment plant. Twocoal-based power stations in the catchment contributeconsiderable Cu and Ni (maximum concentrations 562 and157 μg g-1, respectively) to ambient fluvialsediments, possibly from cooling towers and coalstorage areas. The highest Co and Cr concentrations(113 and 490 μg g-1) in fluvial sediments ofthis catchment are associated with coal-miningactivities. Selective extraction indicates that about50% of the anthropogenic fraction may bebioavailable, whereas sequential extraction proceduressuggest that <25% is associated with the easilyexchangeable/adsorbed phase.Two dams restrict the migration of heavy metals downthe Coxs River and sediment discharging into LakeBurragorang is low in metals.