Relatively little is known about the effects of pollutants on shell biomineralization in molluscs. In the Pacific oyster, Crassostrea gigas, exposure to tributyltin results in the production of a gelatinous substance within the shell and shell deformity (Alzieu et al. 1986), whereas exposure of the mussel, Mytilus californianus, to barium results in abnormal shell calcification (Spangenberg & Cherr 1996). In one of the few studies to investigate the effects of dietary pollutant exposure on shell biomineralization, high (500 g g−1) dietary concentrations of lead resulted in a 25% reduction in shell mass in juvenile garden snails (Helix aspersa), yet shell size was unaffected by lead (Beeby et al. 2002). Similarly, transplanted Crassostrea gigas exposed to high concentrations of cadmium,copper and zinc in Chesapeake Bay had significantly thinner shells than control oysters (Frazier 1976). High concentrations of cadmium have also been shown to inhibit shell growth in Crassostrea virginica (200 g L−1, Shuster & Pringle 1969) and Mytilus edulis (500 g L−1, Sturesson 1978). Exposure of C. gigas to lead for 4 months led to significant differences in the amino acid profile of the shells (Almeida et al. 1998). Shell length growth in M. edulis is significantly reduced by exposure to the heavy metals zinc,mercury, copper, and cadmium but not lead and nickel (Strömgren 1982), and various hydrocarbon mixtures (Strömgren 1986,Strömgren et al. 1986). Given that high levels of pollutants alter shell production in many species of molluscs, it is possible that exposure to pollutants could alter shell growth in pearl oysters.