| Summary: | EPA's existing RfD of 0.1 g/kg/day is based on a poisoning episode in Iraq. Results for two large epidemiological studies in the Faroe Islands and Seychelles Islands have become available since the 1995 IRIS entry. The Faroe Islands study identified associations between in utero methylmercury exposure and deficits on a number of endpoints, as did the New Zealand study. In contrast, the Seychelles Islands study found little or no evidence of impairment. These studies underwent a comprehensive review by the National Research Council (NRC) National Academy of Sciences, along with a smaller study from New Zealand. The NRC performed benchmark dose (BMD) analyses of a number of neuropsychological endpoints from each study. In the assessment being descrived here EPA used the NRC analyses as the basis for the derivation of an RfD for methylmercury. Based on BMDLs (lower limit on the BMD) for a number of endpoints from the Faroe Islands study, as well as an integrative analysis of all three studies, an RfD for 0.1 g/kg/day was derived. This included a total uncertainty factor of 10 for intrahuman toxicokinetic and toxicodynamic variables.
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