Copper bioavailability and amelioration of toxicity in Macquarie Harbour, Tasmania, Australia

The 100-year operation of the Mount Lyell Mining and Railway Company Limited's copper mine in Queenstown, Australia, has resulted in the deposition of over 100 million cubic metres of mine tailings, smelter slag and topsoil into the King River and Macquarie Harbour. A preliminary risk assessment, together with chemical measurements of dissolved copper, ASV-labile copper, copper complexing capacity and resin-adsorbed copper, suggested that copper in mid-salinity harbour waters was potentially bioavailable. However, toxicity tests based on inhibition of microalgal (Nitzschia closterium) growth showed that copper in these waters was not toxic, even though labile copper concentrations (6-24 μg L-1) exceeded the concentration of lowest observable effect for algae of 5 μg L-1. Measurements of intracellular and membrane-bound copper confirmed that cell division was not affected because copper was not taken up intracellularly. Amelioration of copper toxicity was due to binding of dissolved organic matter and/or other metals at the cell membrane, preventing copper binding and uptake. An understanding of the mechanism of copper toxicity and its amelioration is vital to assessing various clean-up options for the harbour.