Foodweb transfer and associated human exposure to methylmercury in Flathead Lake, Montana, USA
Reintroducing traditional foods into Indigenous contemporary diets can improve human health outcomes but may increase exposure to toxins, such as methylmercury (MeHg) in fish. This study examined the Confederated Salish and Kootenai Tribes (CSKT) Lake Trout ( Salvelinus namaycush [Walbaum, 1792]) suppression program in Flathead Lake, Montana, USA, a management strategy to restore the native fishery that may affect the food web and MeHg biomagnification rates. CSKT sells harvested Lake Trout ≤610 mm in length in local markets, donating a portion to local food pantries. We asked 1) To what extent do length and trophic level control MeHg concentrations in Lake Trout, Lake Whitefish ( Coregonus clupeaformis [Mitchill, 1818]), and Bull Trout (Salvelinus confluentus [Suckley, 1859]) in Flathead Lake? and 2) What are the health outcomes for Tribal women of childbearing age consuming fish fillets donated to local food pantries by CSKT? We calculated the MeHg biomagnification slope; modeled relationships between fish length, trophic position, and MeHg concentration; used probabilistic modeling to assess safe fish-consumption levels; evaluated fish-consumption habits of Tribal women; and estimated a benefit–risk quotient (BRQ) for Lake Trout. The MeHg biomagnification slope was 0.18 (CI: 0.17, 0.19), similar to oligotrophic, temperate lakes where Lake Trout are the top predator. Fish length and C and N isotope ratios explained 88% of the variation in log e (MeHg) concentration in Lake Trout. Fish-consumption rates among Tribal women were below federal MeHg exposure limits. Our models suggested 1 serving of Lake Trout per week poses minimal risk of exceeding MeHg intake guidelines. However, to meet essential fatty acids (EFA) intake recommendations, our BRQ analysis suggests Lake Trout should be consumed alongside fish with higher EFA and lower MeHg. Our interdisciplinary analysis suggests CSKT’s natural resource management strategy is likely a key factor in influencing MeHg accumulation in the Flathead Lake food web and subsequent transfer to people.