Methyl mercury: loaves versus fishes

Large numbers of individuals suffered severe neurological effects from poisoning with methyl mercury from the consumption of fish contaminated by industrial discharge in Minamata in the 1950s and 1960s and from bread made from fungicide-treated wheat in the early 1970s in Iraq. In both episodes, infants exposed in utero showed developmental delays. Data from Iraq permitted the estimation of dose-response relationships and provided evidence of greater sensitivity of the foetal brain compared to adult. Studies in a number of communities regularly consuming fish have sought to determine whether and at what level of prenatal exposure neurodevelopment defects may be detected, but the findings do not present a consistent picture. Benchmark analysis using data from Iraq and the three largest studies (New Zealand, Faroes, and Seychelles) suggest an overlap in estimated dose corresponding to a 10% increase in prevalence of adverse effects above background level. However, the Seychelles study, examining children up to 9 years of age, has not found a consistent pattern of adverse developmental effects; a possible explanation may be the presence of micronutrients in the ocean fish diet that enhance brain development and/or counter the toxic effects of methyl mercury.