| Summary: | Hydroelectric reservoir creation accelerates microbial conversion of inorganic mercury (Hg) to bioaccumulative, neurotoxic methylmercury (MeHg). This thesis forecasts MeHg production in flooded reservoirs based on soil organic carbon content and probabilistically models the exposure impacts on local human populations by considering as a case study the Inuit settled downstream from hydroelectric development on the Churchill River, Labrador, Canada. Expected riverine MeHg levels there are approximately ten times present-day average values. Mean MeHg exposures are forecasted to double following flooding and over half of the women of childbearing age and young children in the most northern community are projected to exceed the U.S. EPA’s reference dose. Equal or greater impacts on aqueous MeHg are expected at 11 sites across Canada, suggesting the need for remediation measures prior to flooding or screening of potential sites for human health impacts. Coupled hydrodynamic and biogeochemical simulation of the downstream estuary suggests that estuarine MeHg concentrations increase by 1.2–2.2 times seasonal baseline average. High trophic-level species that contribute most to MeHg exposures are also the basis of indigenous peoples’ traditional diets, contributing disproportionately to intake of polyunsaturated fatty acids and vitamins B12 and D. This analysis supplements traditional food consumption data for Labrador Inuit with publicly available food subsidy records and nutritional databases. While traditional foods account for < 10% of overall calories consumed, they are the main source of MeHg (70%), PCBs (>90%) and a disproportionate source of omega-3 fatty acids (36%) and vitamin D (39%). This analysis calculates the nutritional impacts of substituting higher-MeHg traditional foods with store-bought foods and forecasts health impacts using dose-response functions. Substitution reduces but does not eliminate neurodevelopmental impacts. The relative risk (RR) of cardiovascular mortality is greater for substitution scenarios (population mean RR up to 1.5) than for a baseline diet with MeHg content up to eight times current levels. Substitution generally increase population-wide cancer risks (mean RR up to 1.02) relative to baseline and are associated with a decline in sufficiency of key nutrients (e.g., iron, phosphorus). Dietary advisories alone therefore cannot be used to mitigate risks associated with increased exposures to MeHg. Environmental Health
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