Professor Yanxu Zhang reveals the impacts of climate change on methylmercury formation and bioaccumulation


On Feb 5, 2021, One Earth published a paper titled Impacts of climate change on methylmercury formation and bioaccumulation in the 21st century ocean by Professor Yanxu Zhang and his research group. Results project the influence of climate-induced changes on methylmercury (MeHg) formation and bioaccumulation in the global ocean.

Mercury (Hg) is a global toxicant of concern. Its organic form, monomethylmercury (CH3Hg), has been associated with neuro-cognitive deficits in children and impaired cardiovascular health in adults. In most countries, human CH3Hg exposure occurs predominantly through seafood consumption. CH3Hg in the ocean is mainly formed in situ from atmospherically deposited inorganic Hg and transformed by ocean anaerobic bacteria. CH3Hg efficiently bioaccumulates in marine food webs with the largest magnification between seawater and plankton. The first global treaty aimed at reducing anthropogenic Hg releases (the Minamata Convention) entered into force in 2017 ( Evaluating the effectiveness of this treaty requires diagnosing the roles of anthropogenic Hg emissions and climate-driven changes for future CH3Hg exposures.

Figure. Climate-driven changes in MeHg concentrations in the  surface ocean in 2100

Simulated changes in surface ocean (100m) seawater methylmercury concentrations in the year 2100

The authors use a 3D model to examine how MeHg might response to changes in primary production and plankton community driven by ocean acidification and alterations in physical factors (e.g., ocean temperature, circulation). Productivity changes lead to significant increase in seawater MeHg in the polar oceans and a decrease in the North Atlantic Ocean. Phytoplankton MeHg may increase at high latitudes and decrease in lower latitudes due to shifts in community structure. Ocean acidification might enhance phytoplankton MeHg uptake by promoting the growth of a small species that efficiently accumulate MeHg. Non-linearities in the food web structure lead to differing magnitudes of zooplankton MeHg changes relative to those for phytoplankton. Climate-driven shifts in marine biogeochemistry thus need to be considered when evaluating future trajectories in biological MeHg concentrations.

Yanxu Zhang and Elsie M. Sunderland from Harvard University designed the study;  StephanieDutkiewicz from Massachusetts Institute of Technology provided the ocean biogeochemical dataset; and Y.Z. and E.M.S. wrote the paper. The study was supported by the National Science Foundation of China (NNFS) 41875148, start-up funds from the Thousand Youth Talents Plan, Jiangsu Innovation and Entrepreneurial Talents Plan, and the Collaborative Innovation Center of Climate Change, Jiangsu Province, the U.S. National Science Foundation (OCE 120464) and NASA (80NSSC17K0561).

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