Zinc, cadmium, copper, and manganese in species of finfish and shellfish caught in the Derwent Estuary, Tasmania

Abstract

Thirty-nine marine species, including members of the Teleostorni and Elasmobranchii, were obtained from the River Derwent and analysed for four heavy metals known to be accumulated by certain species, particularly molluscs. Of the muscle tissues from edible Teleostomi and Elasmobranchii all contained levels of zinc, cadmium, and copper well below the maximum levels permitted by current Tasmanian food regulations. Manganese levels were also low. Small species differences for zinc and copper levels in muscle tissue are evident among these finfish. These are probably attributable to differences in feeding habits. Comparison of the metal levels in these species with levels reported by various overseas workers indicate no abnormal accumulation of heavy metals in muscle tissues. With some minor exceptions no relationships existed between the tissue metal levels and length of the fish. Two edible species of molluscs, the native oyster and the common mussel, contained much higher levels of the four metals. For both species levels of zinc and cadmium exceeded the levels specified by the food regulations. The data presented indicate that the ability of molluscs to accumulate certain metals, particularly zinc and cadmium, to abnormally high levels is not shared by finfish species. The fact that elevated metal concentrations in seawater are not reflected in the muscle tissues of finfish means that the monitoring of commercial fish species caught in the River Derwent would provide a much less sensitive index of pollution than would the monitoring of oysters or mussels.