The concentrations of selected trace metals were measured in commercially harvested New Zealand scallop species: Chlamys delicatula (queen scallop) from the Otago Coastal Shelf and Pecten novaezelandiae (dredge scallop) collected from 6 sites around the South Island, New Zealand (Titirangi Bay, Collingwood, Milford Sound, Breaksea Sound, Paterson Inlet, and the Chatham Islands). Bivalves were dissected into individual parts, the tissues lyophilized by freeze-drying, and then digested by heating with concentrated HNO3 and H2O2. The resulting solutions were analyzed by inductively coupled atomic emission spectrophotometry to determine the Cd, Cu, Zn, and Fe concentrations. For P. novaezelandiae, the trace metals in whole body tissues were site-specific with mean values ranging from 18–59 µg/g dry weight (dwt) for most sites and high Cd in scallops collected from the Chatham Islands (mean, 332 µg/g dwt). Cu concentrations were low, 6–11 µg/g; average concentrations of Zn ranged from 57–127 µg/g, and mean Fe values ranged from 197–2,324 µg/g. For C. delicatula the whole body tissue concentrations for Cd were 65 µg/g; for Cu, 6 µg/g; for Fe, 49 µg/g; and for Zn, 50 µg/g. The Cd concentrations were highest in digestive gland > gills > adductor muscle (striated and smooth) > gonad ∼ mantle. Particularly notable was the average Cd level of 3,985 ± 1,108 µg/ g dwt in the digestive gland and viscera of P. novaezelandiae collected from the Chatham Islands. The highest average Cu level was also measured in the digestive gland of both species. A higher average Fe level was measured in the gills of P. novaezelandiae (2,374 µg/g) compared with the gills of C. delicatula (133 µg/g). Trace metal concentrations in the scallop tissues did not correlate with any known environmental contaminants. Preliminary biochemical measurements using salt precipitation and dialysis indicated variable proportions of Cd bound to a protein with a molecular weight greater than 3,500 Da, depending on the scallop species and collection site. The Cd concentrations in P. novaezelandiae may be influenced by the Subtropical Convergence, with low Cd in areas more remote from this global oceanic current and highest values for samples from the Chatham Islands located within it. It was concluded that some scallop tissues may be useful as biomonitors for specific metals and that the characteristic metal signatures would be useful for fisheries management and compliance purposes in identifying scallops from various areas.
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Vol. 29 • No. 2