Determining natural ‘backgroundʹ concentrations of trace metals in oysters from New South Wales, Australia

The use of bivalves to indicate spatial and temporal patterns in the distribution of bioavailable metals is well established. The interpretation of patterns is, however, often confounded by natural variations in metal concentrations which result from geological factors. This paper presents a method of using clustering and principal component analyses to determine background concentrations of metals in the oyster Saccostrea commercialis sampled from 20 estuaries in New South Wales, Australia. The method identified the estuaries which contained oysters with significantly different suites of metals from those in estuaries with obvious anthropogenic inputs of metals, allowing the calculation of natural ranges of metals in oysters. It also demonstrated which metals showed the greatest natural variability and which metals were indicative of urbanisation in the catchment.