Investigation of anthropogenic trace metals in sediments of Lake Illawarra, New South Wales

Abstract

Surficial (<2 cm) and subsurface (cores 20 – 50 cm deep) sediments from Lake Illawarra were analysed for trace metals (Cd, Cu, Pb, Zn) to determine the extent and nature of anthropogenic influence. Sediment samples were size-normalised (<62.5 μm) to determine total acid-extractable metals in the fine fraction, as well as in whole sediment. A four-step sequential extraction technique was used to determine major chemical phases, whereas 1 M HCl, 0.05 M ethylenediamine tetra-acetic acid (EDTA) treatments gave an estimate of the bioavailable portion of the metals. The acid-volatile sulfide simultaneously extracted metals (AVS-SEM) technique was used to provide information on sediment toxicity. Griffins Bay is the most contaminated part of Lake Illawarra and is a major sink for trace metals. The source of metals to this embayment is primarily input from creeks draining the urban and industrial areas of the Port Kembla industrial complex, as opposed to direct atmospheric deposition, as is commonly believed. Trace metals in sediments of Griffins Bay are probably not bioavailable under current physico-chemical conditions, although oxidation of the sediment by anthropogenic or natural processes may result in the conversion to more bioavailable chemical forms.

Key words:

• bioavailability
• enrichment
• geochemical background
• Lake Illawarra
• sediments
• trace metals

Acknowledgements

We would like to thank Bryan Chenhall (University of Wollongong), for his valuable help and advice, Tom Savage and Stephanie McCready, for their assistance and guidance in the laboratory, and Gary Clarke (Lake Illawarra Authority), for background information on the lake. The constructive comments made by the reviewers are greatly appreciated.