Heavy metal pollution of coastal river sediments, north-eastern New South Wales, Australia: lead isotope and chemical evidence

Heavy metal and metalloid concentrations within stream-estuary sediments (<180-mu m size fraction) in northern-eastern New South Wales largely represent natural background values. However, element concentrations (Ag, As, Cd, Cr, Cu, Hg, Ni, Pb, Sb, Zn) of Hunter River sediments within the heavily industrialized and urbanized Newcastle region exceed upstream background values by up to one order of magnitude. High element concentrations have been found within sediments of the Newcastle Harbour and Throsby Creek which drains into urbanized and light industry areas. Observed Pb enrichments and low Pb-208/Pb-204, Pb-207/Pb-204 and Pb-206/Pb-204 ratios are likely caused by atmospheric deposition of Pb additives form petrol and subsequent Pb transport by road run-off waters into the local drainage system. Sediments of the Richmond River and lower manning, Macleay, Clarence, Brunswick and Tweed river generally display no evidence for anthropogenic heavy metal and metalloid contamination (Ag, As, Cd, Cr, Cu, Hg, Ni, Pb, Sb, Zn). However, the rivers and their tributaries possess localized sedimentary traps with elevated heavy metal concentrations (Cu, Pb, Zn). Lead isotope data indicate that anthropogenic Pb provides a detectable contribution to investigated sediments. Such contributions are evident at sample sites close to sewage outlets and in the vicinity of the Pacific Highway. In addition, As concentrations of Richmond river sediments gradually increase downstream. This geochemical trend may be the result of As mobilization from numerous cattle-dip sites within the region into the drainage system and subsequent accumulation of As in downstream river and estuary sediments.