Uptake of cadmium, zinc, copper, lead and chromium in the pacific oyster. Crassostrea gigas. Grown in the tamar river. Tasmania

Hundreds of oysters and mud samples from 15 sites along the Tamar River were analysed for cadmium, copper, zinc, lead and chromium. The widely accepted concept of enrichment factors of up to several hundred thousand, describing accumulation by oysters of cadmium, zinc and copper from seawater has been found to be grossly misleading. Concentrations found for these three metals in oysters were only 10–40 times the concentrations in inhabited muds. Concentrations of metals in muds may be used to indicate whether a potential oyster bed would produce oysters that were grossly contaminated. Approximately 1 ppm cadmium in mud could result in oysters containing at least 25 ppm, i.e. 4–5 ppm wet wt. Similarly. 100 ppm zinc in mud could produce oysters containing at least 4000 ppm. i.e. 800–1000 ppm wet wt. Three heavy metal accumulation processes were discernible. Copper and chromium appeared to be absorbed up to a maximum weight that was limited by the size of the oyster and was independent of the amount of metal in the mud. Lead was not absorbed through any physiological demand, but was randomly incorporated at sites containing high concentrations in the mud. Zinc and cadmium were accumulated by a process that depended primarily on the concentrations of these metals in the mud at each site. Mean dry wt concentrations of metals in oysters and mud samples ranged from: 4.2–134 ppm and 0·4 to 5·7 ppm cadmium; 200–1700 ppm and 3–224 ppm copper: 0 135 ppm and 4–1500 ppm lead: 1–37 ppm and 2–88 ppm chromium; 1700 14.000 ppm and 20–500 ppm zinc. respectively.