Heavy Metals in Marine Biota, Sediments and Waters from the Shark Bay Area, Western Australia
Keywords:Shark Bay, Cadmium, Heavy metals, Molluscs, Metal uptake rates, Nearshore sediments, Metals in water
Shark Bay, Western Australia, is geographically remote from all known industrial and geological sources of heavy metals. Surprisingly, several species of mollusc found here have cadmium contents which exceed both the usual limits of 2 ppm wet weight for molluscs taken for human consumption, and levels found in molluscs from areas of recognised heavy metal pollution. We know of no other pollution-free locality where similarly high cadmium concentrations are found in molluscs. The cadmium content of several species of Shark Bay moll uses frequently exceeds 5 ppm wet weight, locally exceeds 10 ppm, and shows substantial regional variation within the embayment. Some regionally variable factors which could influence the rate of cadmium uptake include, an anthropogenic source, species variation, and salinity variation, but these possibilities are precluded by the data. Other regionally variable factors include, dissolved cadmium concentrations, substrate sediment composition, and local groundwater influx, but present data do not reveal a satisfactory explanation for the regional variation observed. The selective concentration of cadmium in the adductor muscle of the pearl oyster (Pinctada Carchariarium) and curiously high cadmium/zinc ratios are described. Various methods are evaluated for reducing the cadmium content of Shark Bay molluscs prior to human consumption. These include, selection by size and location, discarding the adductor muscle, and leaching in brine.