John Wiley & Sons, Ltd.

Pre‐anthropocene mercury residues in North American freshwater fish

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Courtesy of John Wiley & Sons, Ltd.

Mercury has been entering the environment from both natural and anthropogenic sources for millennia, and humans have been influencing its environmental transport and fate from well before the Industrial Revolution. Exposure to mercury (as neurotoxic monomethylmercury (MeHg)) occurs primarily through consumption of finfish, shellfish, and marine mammals, and regulatory limits for MeHg concentrations in fish tissue have steadily decreased as information on its health impacts has become available. These facts prompted us to consider two questions: (1) What might the MeHg levels in fish tissue have been in the pre‐Anthropocene, before there were significant human impacts on the environment? and (2) How would these pre‐Anthropocene levels have compared to current regulatory criteria for MeHg residues in fish tissue? We addressed the first question by estimating pre‐Anthropocene concentrations of MeHg in the tissues of prey and predatory fish with an integrated mercury speciation, transport and fate, and food web model (SERAFM), using estimated mercury concentrations in soil, sediment, and atmospheric deposition prior to the onset of significant human activity (i.e., ≤ 2000 BCE). Model results show MeHg residues in fish varying depending on the characteristics of the modeled water body, which suggests that mercury in fish tissue is best considered at the scale of individual watersheds or water bodies. We addressed the second question by comparing these model estimates to current regulatory criteria and found that MeHg residues in predatory (but not prey) fish could have approached or exceeded these criteria in some water bodies during the pre‐Anthropocene. This suggests that there may be naturally‐occurring levels of mercury in fish below which it is not possible to descend, regardless of where those levels stand with respect to current regulatory limits. Risk management decisions made under these circumstances have the potential to be ineffectual, frustrating, and costly for decision makers and stakeholders alike, suggesting the need for regulatory flexibility when addressing the issue of mercury in fish. Integr Environ Assess Manag © 2013 SETAC

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