HEAVY-METAL CONCENTRATION IN OYSTER CRASSOSTREA-MADRASENSIS (BIVALVIAANISOMYARIA) FROM THE UPPANAR, VELLAR AND KADUVIAR ESTUARIES OF SOUTHEAST COAST OF INDIA/

Spatial and temporal variation in concentration of essential elements Cu and Zn and non-essential elements Cd and Pb in the whole body and o rgans namely gill, mantle and adductor muscle of oyster Crassostrea ma drasensis were studied over a two year period. The Cu and Zn level wer e highest in the tissues of oysters in Kaduviar estuary. Cd and Pb con centrations were similar in all the estuaries. Metal levels in the tis sues were in the order of gill > mantle > adductor muscle. Seasonal va riation of tissue metal concentration was observed, with higher levels during the monsoon and lower levels in summer. Metal levels in the oy ster was in the order of Zn > Cu > Pb > Cd. This order reflects the me tal levels in the ambient medium.