Professor Yanxu Zhang reveals the global health effects of future atmospheric mercury emissions


On May 24, 2021, Nature Communications published a paper titled “Global health effects of future atmospheric mercury emissions” by Professor YanxuZhang and his research group. This study projects the future impacts of atmospheric mercury emissions on global human health.

Mercury (Hg) is a global toxicant of concern, with the organic form, methylmercury (MeHg), associated with neuro-cognitive deficits in children and fatal heart attacks in adults. To protect human health and the environment, the Minamata Convention on Mercury, a legally-binding international treaty, took effect in August 2017 to reduce anthropogenic emissions of Hg. However, its implementation effects have not been evaluated.

MeHg exposure to human is influenced by a chain of processes including atmospheric emission, atmospheric transport and deposition, air-sea exchange, air-land exchange, chemical transformation (especially Hg methylation), food web transfers, and human food intake. These processes are modulated by the fluctuation and change in climate, land-use, ocean circulation, and ecosystem functions. This study develops a more comprehensive approach to project the change in human MeHg exposure responding to Hg emission changes. The authors integrate changes in anthropogenic emissions, climate, and biogeochemical cycles into a coupled three-dimensional atmosphere/ocean and two-dimensional land model. The Hg/MeHg levels in the environment are used to scale an intake inventory of MeHg for different countries, which are further used to calculate the health impact based on epidemiology-based dose-response relationships. This study presents a map of MeHg-related health risks for all the countries for the first time, then translates future (until 2050) Hg emission projections into health risks.


Fig. 1 Global health impact of methylmercury (MeHg) food exposure at present-day. (a) Per-fetus intelligence quotient (IQ) decrement; (b) Fatal heart attack deaths; (c) Economic loss from IQ decrease; (d) Value of statistical life (VSL) loss from fatal heart attacks; (e) Total loss from MeHg exposure (the sum of (c) and (d)). Economic losses are in United States (US) dollars (2020 value and adjusted by purchasing power parity). The gray area indicates missing data and the color scale of (c)–(e) is in the logarithmic scale.

Results estimate that the global health impacts associated with MeHg exposure for the general population are $117 billion, contributed by 1.2×107 points of IQ decrements (0.086 point per-fetus) and 29,000 deaths per year at present-day (Fig. 1). The health risk associated with MeHg exposure based on food intake inventory and food MeHg concentrations for individual countries at a global scale. Coastal countries that consume more seafood have the greatest health risks, and countries that consume less fish and rice have the least health risks.

Five policy scenarios are developed for the emissions during 2010-2050 based on present studies (Fig. 2). The most optimistic scenario (maximum feasible reduction, MFR) leads to Hg levels in the freshwater and marine biota half of the present-day levels. Atmospheric Hg deposition and marine planktonic MeHg are highly sensitive to future Hg emissions, while the changes in soil Hg concentrations are much smaller. The model projects that the MFR and NP-Delayed scenarios reduce the atmospheric deposition in 2050 by 48% and 28%, respectively. And the A1B (business as usual) and the A2 (divided world) scenarios project an increase of deposition by 87% and 59%, respectively.


Fig. 2 Projected mercury levels in the environment in 2050. The column (a), (b), and (c) is for atmospheric deposition, soil, and marine plankton, respectively. For each column, the top panel shows the trend of global mean values, while the lower panels are the spatial distribution for the five scenarios (with emission from highest to lowest): A1B (business as usual), A2 (divided world scenario), CP (current policy), NP-Delayed (new policy delayed), and MFR (maximum feasible reduction).

The changes in future primary anthropogenic emissions are substantially dampened for their health effects. The total IQ decrease in 2050 predicted by the MFR and NP-Delayed scenarios are 24% and 15% lower than that of the CP scenario, respectively, even though the anthropogenic emissions have been projected to decrease by 85% and 48%, respectively. The A1B and A2 scenarios predict a 51% and 34% increase in the IQ effect, respectively, whereas the changes in primary emissions are 150% and 99%, respectively (Fig. 3a). The CP scenario projected acumulative death of 1.6 million during 2010-2050. The projected trajectory for the deaths of MFR and NP-Delayed scenarios is quite flat, with acumulative death of 1.4 and 1.5 million, respectively. In contrast, the projected deaths for A1B and A2 scenarios are 120%and 94% higher than the level in 2010, amounting to a cumulative death of 2.0 and 1.9 million, respectively(Fig. 3b).


Fig. 3 Trajectories of global annual health effects associated with different future emission scenarios. (a) Total intelligence quotient (IQ) decrements ofnewborns; (b) Total heart attack deaths; (c) Economic valuation of health effects: total valuation (solid lines) and from IQ decrements (dashed lines). Fivescenarios are included: A1B, A2, CP, NP-Delayed, and MFR.

The cumulative economic loss for the CP scenario is $19 trillion. The projected health benefits of the MFR and NP-Delayed scenarios compared to the CP scenario are $2.4trillion and $1.5 trillion, respectively. On the other hand, the A1B and A2 scenarios will result in an additional loss of $4.9 trillion and $3.3 trillion, respectively (Fig. 3c).

This study highlights the urgent need for Hge mission reduction that can effectively reduce the health risks associated with MeHg exposure. Moreover, this comprehensive modeling approach provides a much-needed tool to help parties to evaluate the effectiveness of Hg emission controls as required by the Minamata Convention and would assist related countries to make their national action plans.

Professor Yanxu Zhang is the first and corresponding author of this paper. Co-authors on the thesis include Dr. Stephanie Dutkiewicz from Massachusetts Institute of Technology, ProfessorShiliang Wu and Dr. Huanxin Zhang from Michigan Technological University, United States, Professor Feiyue Wang from University of Manitoba, Canada, Professor Long Chen from East China Normal University, Professor Shuxiao Wang from Tsinghua University, Researcher Ping Li from Institute of Geochemistry, Chinese Academy of Sciences. The study is financial supported by the National Natural Science Foundation of China (NNSFC) 41875148, the Chinese Academy of Science Interdisciplinary Innovation Team (JCTD-2020-20), Jiangsu Innovative and Entrepreneurial Talents Plan, the Collaborative Innovation Center of Climate Change, Jiangsu Province.

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