TRACE-METAL RESIDUES IN SHELLFISH FROM MARYLAND WATERS, 1976-1980

Levels of 7 heavy metal residues, (As, Cd, Cr, Cu, Pb, Hg and Zn) were monitored in samples of the American oyster (Crassostrea virginica), the soft shell clam (Mya arenaria), the hard shell clam (Mercenaria mercenaria) and the blue crab (Callinectes sapidus). Samples were taken from the Maryland section of the Chesapeake Bay and its tributaries over 5 yr (1976-1980). This study was undertaken to provide an estimate of a baseline for values of trace heavy metals. Also, the oyster, being a non-mobile filter feeder, provided information regarding the level of metal residues in its environment (water and sediment), because heavy metal uptake was related to the surrounding metal concentrations. This type of monitoring program was essential to ensure that shellfish sold for human consumption were within safe limits established for toxic substances by the USA Food and Drug Administration. Results of the study were consistent with data from previous years and no statistically significant year-to-year trends were observed.