Neurodevelopmental effects from prenatal exposure to methylmercury in the Seychellois and Faroes cohorts and the critical concentration: a review

Abstract

A workshop on the Scientific Issues Relevant to Assessment of Health Effects from Exposure to Methylmercury was held in Raleigh, North Carolina, November 18-20, 1998. At that time, most discussions focused on two of the major epidemiologic studies, e.g., Seychelles child development study and Faroese birth cohort study, associating methylmercury exposure with an array of developmental measures in children. These two studies seemed to provide different conclusions on the potential health effects of methylmercury and significant uncertainties remained because of issues related to exposure, neurobehavioral endpoints, confounders and statistics, and design. Since then, each group researching the Seychellois or Faroes cohort has reported some new findings on the risk assessment of methylmercury. This article is intended to present an overview of the above research, as well as benchmark dose calculations. One implication is that neuropsychological measures may depend on social and cultural factors including race and language, and another is that a key to resolve whether the exposure has harmed the fetus appears to lie in neurophysiological measures such as brainstem auditory evoked potentials and electrocardiographic R-R interval variability. In addition, it is likely that the findings published tend to underestimate the neurotoxic effects of developmental methylmercury exposure. In light of the precautionary principle, a conclusion on health effects of low-level dietary exposures to methylmercury needs to be drawn from all available data including the New Zealand study.