Heavy Metals in Tasmanian Shellfish 1-Monitoring Heavy Metal Contamination in the Derwent Estuary: Use of Oysters and Mussels

The contamination of an estuary with heavy metals by a single large ore processing plant provided a unique opportunity to assess the use of mussels and oysters as indicators of heavy metal contamination. Field accumulation and depuration experiments, variation of metal content with size and prediction of water movements are described from shellfish surveys covering the Derwent River and adjacent coastal waters. Oysters were found to be suitable for monitoring zinc, cadmium, lead and copper contamination. Mussels were also suitable for monitoring zinc, cadmium and lead, but in this instance were found unsuitable for monitoring copper as the surveys indicate that copper accumulation is suppressed in mussels in a contaminated environment. The rate of accumulation and depuration of metals by oysters and mussels in field trials has been related to the anatomy of the animals and the sequestering of some metals in granulocytes. Uneven metal distribution between gonad and other tissues has been found to cause seasonal variation of heavy metals in oysters.