Eco-Defense against Invasions

consumption of fish has been associated with reduced performance on tests of neurologic function in children, including tests of cogni-tive development, attention and behavior, and motor skills. A comprehensive review of the mercury literature conducted by the National Research Council (NRC) Committee on the Toxicological Effects of Methylmercury concluded that, based on the evidence available, " neurodevelopmental deficits are the most sensitive, well-documented effects " of exposure to mercury (NRC 2000). The NRC committee's conclusion was based primarily on its review of epidemiologic studies conducted in the Faroe Islands Myers et al. 2003). These three populations were selected for study in large part because fish consumption was known to be relatively high; human methylmercury exposure is largely attributable to intake of methyl-mercury that has accumulated in fish tissue. All three studies measured prenatal exposure to mercury and neurodevelopmental end points in the children, though there were differences in the tests used to measure potential neurodevelopmental deficits. The Faroe Islands and New Zealand studies found a statistically significant relationship between higher prenatal mercury exposure and poorer scores on tests of neurologic function, but the Seychelles study did not. The NRC committee determined that " each of the studies was well designed and carefully conducted, and each examined prenatal MeHg [methylmercury] exposures within the range of the general U.S. population exposures " (NRC 2000). The U.S. Environmental Protection Agency (EPA) developed a reference dose (RfD) for methylmercury that draws on the NRC analysis of data from all three epidemio-logic studies. An RfD is an estimate of a daily exposure to the human population (including sensitive subgroups) that is likely to be without an appreciable risk of deleterious effects during a lifetime. However, the U.S. EPA's review also indicates that " no evidence of a threshold arose for methylmercury-related neurotoxicity within the range of exposures in the Faroe Islands study " (U.S. EPA 2001). In addition, the RfD does not provide information about the dose–response relationship between prenatal mercury exposure and related neurologic effects, because it focuses on a single exposure level and does not identify the risk associated with that level. A dose–response model is needed to estimate the potential risk of neurodevelopmental effects in the population and the benefits of any efforts to reduce mercury exposure. We applied a Bayesian hierarchical model to integrate the findings from the three epidemiologic studies and estimate a dose–response relationship between maternal mercury body burden …