Implementation of a Systematic Review Framework to Evaluate the Need for Reassessment of Methylmercury
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Multiple health agencies (Health Canada, 2007; UNEP, 2002; US EPA, 2001, 1997; ATSDR, 1999) and the US National Academy of Sciences (NRC, 2000) have established that prenatal oral exposure to methylmercury in humans causes developmental neurotoxicity (DNT). The existing US EPA quantitative assessment of methylmercury dose-response was developed by the IRIS (Integrated Risk Information System) program in 2001. That assessment derived a reference dose (RfD) based on DNT effects in children following prenatal exposure using information from 3 epidemiological cohorts in several publications. The RfD of 0.1 µg/kg-day was derived from multiple DNT measures related to cord blood concentrations of 46–79 µg/L, which the assessment estimated corresponded to maternal daily intakes of methylmercury during pregnancy of 0.86–1.47 µg/kg-day. To evaluate the need for a reassessment, we will use systematic review methods (problem formulation, literature search, literature evaluation, and synthesis). This presentation will discuss considerations in evaluation of the new data available for an updated quantitative methylmercury assessment based on the literature search results as well as an initial identification of key scientific issues. A recent literature search found more than 200 epidemiological publications with dose-response information on neurodevelopmental effects in humans of methylmercury exposure pre- and/or postnatally, based on dozens of epidemiological cohorts, including the 3 original ones considered in the 2001 risk assessment. Several scientific issues were identified on initial review of the literature: form of mercury in analytical measurements, biomarkers of exposure, methods used to address confounding in epidemiological studies.