Toward a Global Model of Methylmercury Biomagnification in Marine Food Webs: Trophic Dynamics and Implications for Human Exposure

Marine fish is an excellent source of nutrition but also contributes the most to human exposure to methylmercury (MMHg), a neurotoxicant that poses significant risks to human health on a global scale and is regulated by the Minamata Convention. To better predict human exposure to MMHg, it is important to understand the trophic transfer of MMHg in the global marine food webs, which remains largely unknown, especially in the upper trophic level (TL) biota that is more directly relevant to human exposure. In this study, we couple a fish ecological model and an ocean methylmercury model to explore the influencing factors and mechanisms of MMHg transfer in marine fish food webs. Our results show that available MMHg in the zooplankton strongly determines the MMHg in fish. Medium-sized fish are critical intermediaries that transfer more than 70% of the MMHg circulating in food webs. Grazing is the main factor to control MMHg concentrations in different size categories of fish. Feeding interactions affected by ecosystem structures determine the degree of MMHg biomagnification. We estimate a total of 6.1 metric tons of MMHg potentially digested by the global population per year through marine fish consumption. The model provides a useful tool to quantify human exposure to MMHg through marine fish consumption and thus fills a critical gap in the effectiveness evaluation of the convention.