Dietary exposure to lead: The mean total dietary exposure to lead for all respondents ranged from 2–6 per cent PTDI, and for high consumers, 6 per cent of the PTDI. For groups considered at risk from lead exposure (namely, 2-year-old children) total dietary exposure to lead was 5–17 per cent PTDI for mean consumers and 15–35 per cent for high consumers (ANZFA 1999b).
Ranking of hazard: Lead is ranked as ‘severe’ in terms of adverse health effects (Section 3, Table 3) because of its potential to be life-threatening or cause ongoing illness following chronic exposure.
Mercury
Mercury occurs naturally in the environment as elemental, inorganic and organic mercury. Methylmercury, a form of organic mercury, is the most hazardous form of mercury encountered in food. Fish and other seafood is the main source of exposure to methylmercury for most individuals.
Methylmercury is largely produced from the methylation of inorganic mercury by certain micro-organisms present in marine and freshwater sediments. Once produced, methylmercury is rapidly taken up and concentrated by filter feeding organisms, upon which other fish feed. This process results in the steady accumulation of methylmercury in the aquatic food chain, with all fish containing small amounts of methylmercury in their muscle tissue. Those species at the top of the food chain (for example, predatory fish or marine mammals) tend to accumulate the largest amount of methylmercury.
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