Arsenic, cadmium, mercury, zinc and lead: ANZFA reviewed the public health risks due to heavy metal contamination in foods (including molluscan shellfish) in 1999 [5,7]. Data on concentrations of heavy metals in foods was used to provide a total-diet estimate of exposure. The results were as follows:
For arsenic, dietary modelling indicated that high consumers of molluscs could receive up to 6 per cent of the provisional tolerable daily intake (PTDI) for inorganic arsenic from molluscs, based on an inorganic arsenic content of seafood of 6 per cent of the total arsenic content.
For mercury, ANZFA concluded that molluscs contribute only 0.17 per cent to total dietary exposure to mercury [7], and that even high consumers were unlikely to approach the provisional tolerable weekly intake (PTWI).
For zinc, ANZFA [7] estimated that high consumers of oysters would approach 38 per cent of the PTDI. However, ANZFA concluded that it was likely that dietary exposures were overestimated and that exposure to zinc at the mean and high dietary exposures posed only a relatively low risk to human health.
For lead, ANZFA [7] estimated that molluscs contribute approximately 0.6 per cent to the total dietary exposure. However, as lead exposure occurs through many exposure routes, a maximum limit for lead in molluscs was established due to the serious nature of lead toxicity and consistent with an overall goal of reducing blood lead levels in the general population.
For cadmium, FSANZ performed a recent dietary exposure assessment in 2000. Dietary exposure to cadmium was estimated to be 52 per cent of the PTDI (calculated as the PTWI divided by 7) at the median daily level of consumption of oysters, and 7.9 per cent of the PTDI at the median daily level of consumption of mussels. However, as oysters and mussels are only occasionally eaten foods, with 94 per cent of the population consuming them less than once per week, this level of exposure would not be expected to occur on a daily basis.
