FDA Perspectives on Methylmercury in Fish
P. Michael Bolger, Ph.D., D.A.B.T., Chief, Contaminants Branch, Center for Food Safety and Applied Nutrition, US Food and Drug Administration, Washington, DC
Methylmercury (MeHg) is an environmental contaminant which ultimately arises from both natural (e.g. volcanic) and human-derived sources (e.g., coal derived power generation). It is enriched in the food chain, specifically the aquatic food chain, with the highest levels found in certain larger, long-lived fish. Information from several poisoning episodes in Japan and laboratory animal experiments prompted the FDA to establish an action level of 1 ppm in 1979. MeHg is almost completely absorbed from the gastrointestinal tract and the primary target organ is the nervous system. Humans may be particularly susceptible to the toxic effects of MeHg because of the potential susceptibility of the developing nervous system. Effects on the fetus may occur in a dose-response range lower than for effects in adults (e.g. paraesthesia). Since the earlier poisoning episodes newer information has been published from well designed prospective studies which specifically analyzed the effect of low level MeHg exposure via fish consumption on neurological development. The potential differential sensitivity between the adult and the fetus is a critical issue in the context of safety/risk assessment. Depending on the dataset the use of the traditional safety/negligible risk assessment paradigm can result in an answer which identifies certain levels of exposure to be unsafe. This process has always been useful in providing a yes or no answer, but it does not describe the risk in an absolute sense, nor does it provide a means of gauging the level of effort appropriate for reducing the risk above the safe level of exposure. The determination of appropriate public health measures required to mitigate MeHg exposures requires quantitative estimates of the risks associated with degrees of exposure of MeHg. The risks of MeHg exposure must be weighed against the benefits of fish consumption and the extent to which this is accomplished will directly influence the degree to which public health decisions are well informed.