DEPURATION OF COPPER AND ZINC BY GREEN OYSTERS AND BLUE MUSSELS OF TAIWAN

This paper describes depuration processes of copper and zinc in green oysters (Crassostrea gigas) and in blue mussels (Mytilus smarangdium) collected from an environment with heavy copper contamination, and the n transferred to natural clean seawater. Results show that the total l oss of copper content per oyster is an exponential function of exposur e time for the first 6 days with a depuration rate of 351 mug g-1 day- 1 and then levels off. During this exponential decrease period approxi mately 67% of the copper accumulated in green oysters was depurated. H owever, when the copper contents in the oysters decreased from 2225 +/ - 111 mug g-1 to 344 +/- 18.7 mug g-1 the depuration rates decreased f rom 245 mug g-1 day-1 to 0.08 mug g-1 day-1. This means that green oys ters had a 16-fold higher copper depuration rate (351 mug g-1 day-1) t han normal oysters (21.5 mug g-1 day-1) for the first 6 days. However, the depuration of accumulated copper and zinc by the mussels was a fa st process in natural clean seawater. About 91% of the accumulated cop per was lost during the first 6-day period; copper contents declined f rom 20.2 +/- 3.41 mug g-1 to 1.80 +/- 0.21 mug g-1. Only 36% of the ac cumulated zinc was lost during a depuration period of 6 days. Calculat ions show that the biological half-lives of copper in green and normal oysters were 11.6 and 25.1 days, respectively. The biological half-li ves of zinc in green and normal oysters were 16.7 and 30.1 days, respe ctively. In spite of the relatively low initial copper content in blue mussels being 20.2 +/- 3.41 mug g-1, the biological half-life is only 6.40 days. From these results it is important to emphasise that the f astest turnover rate is for copper in blue mussels. However, zinc is m ore retentive in blue mussels than copper.