42 - Increased Light May Halve Surface Seawater Methylmercury in 2100

Human exposure to methylmercury (CH3Hg), a potent neurotoxin, is principally through the consumption of seafood. The formation of seawater CH3Hg and its bioaccumulation in marine food webs experience ongoing impacts of global climate warming and ocean biogeochemistry alterations. However, the net effects largely remain unknown due to multiple acting synergistic and antagonistic factors. Here we employ a global ocean model driven by projected future climate to show a 54% decrease in the surface ocean seawater CH3Hg concentrations and a 43% decrease in the bioconcentration of CH3Hg in phytoplankton by the end of the 21st century. This mainly results from the advantageous light condition for photodemethylation associated with increased incident short-wave radiation and less attenuation by decreased sea ice and chlorophyll. Our results offer an optimistic premise that alongside global efforts to reduce anthropogenic Hg emissions, we can effectively reduce human CH3Hg exposure and the related human health risk in this century.