From Stockholm to Minamata and beyond: Governing mercury pollution for a more sustainable future

Abstract

The 50th anniversary of the 1972 United Nations Conference on the Human Environment provides an opportunity to reflect on mercury pollution as a sustainability issue past, present, and future. Scientists and policy-makers recognize that mercury is connected to multiple sustainability challenges, but a more comprehensive understanding of global mercury governance in the context of sustainability is needed. Here, in this Review, we synthesize the existing literature and evaluate the global governance of mercury pollution in relation to sustainability. We find that global 50-year trends in mercury production, consumption, and discharges are mixed, but mercury governance has expanded; mercury discharges from coal-fired power plants and artisanal and small-scale gold mining, two leading sectors of mercury pollution, are increasingly connected to sustainability challenges; a global-scale indicator of mercury discharges can provide policy-relevant information, but cannot capture local variations; and long-term interventions addressing mercury use and pollution are part of broader sustainability transitions. The 50th anniversary of the 1972 United Nations Conference on the Human Environment provides an opportunity to reflect on mercury pollution as a sustainability issue past, present, and future. Scientists and policy-makers recognize that mercury is connected to multiple sustainability challenges, but a more comprehensive understanding of global mercury governance in the context of sustainability is needed. Here, in this Review, we synthesize the existing literature and evaluate the global governance of mercury pollution in relation to sustainability. We find that global 50-year trends in mercury production, consumption, and discharges are mixed, but mercury governance has expanded; mercury discharges from coal-fired power plants and artisanal and small-scale gold mining, two leading sectors of mercury pollution, are increasingly connected to sustainability challenges; a global-scale indicator of mercury discharges can provide policy-relevant information, but cannot capture local variations; and long-term interventions addressing mercury use and pollution are part of broader sustainability transitions. IntroductionThe global sustainable development agenda is large, multifaceted, and critical to ensuring human well-being for both current and future generations. A key sustainability challenge involves how to further advance the assessment and governance of hazardous substances that cause environmental and human health problems.1Wang Z. Altenburger R. Backhaus T. Covaci A. Diamond M.L. Grimalt J.O. Lohmann R. Schäffer A. Scheringer M. Selin H. et al.We need a global science-policy body on chemicals and waste.Science. 2021; 371: 774-776https://doi.org/10.1126/science.abe9090Crossref PubMed Scopus (32) Google Scholar Hazardous substances, as part of a focus on novel entities, have also been identified as a major global issue for which some scientists have attempted to classify a planetary-level boundary to inform policy making and management.2Persson L. Carney Almroth B.M. Collins C.D. Cornell S. de Wit C.A. Diamond M.L. Fantke P. Hassellöv M. MacLeod M. Ryberg M.W. et al.Outside the safe operating space of the planetary boundary for novel entities.Environ. Sci. 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Rep. 2018; 8: 6705https://doi.org/10.1038/s41598-018-24938-3Crossref PubMed Scopus (58) Google ScholarGlobal assessment reports over the past two decades have synthesized scientific knowledge of the environmental behavior of mercury and its impact on human health, also informing international cooperation. The first global mercury assessment, completed in 2002, identified mercury as a global pollutant due to long-range atmospheric transport that warranted international action.3United Nations Environment ProgrammeGlobal Mercury Assessment. United Nations, 2002https://wedocs.unep.org/20.500.11822/12297Google Scholar Voluntary partnerships aiming to reduce mercury use and pollution under the United Nations Environment Programme (UNEP) started in the mid-2000s, and UNEP’s Governing Council decided in 2009 to launch negotiations on a global mercury treaty.7Selin H. 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In addition to the global assessments, the Arctic Monitoring and Assessment Programme produced a series of Arctic-focused reports beginning in the 1990s identifying mercury as an environmental pollutant and human health problem.11Arctic Monitoring and Assessment ProgrammeAMAP Assessment 2002: Heavy Metals in the Arctic. Arctic Monitoring and Assessment Programme (AMAP), 2005Google Scholar,12AMAPAMAP Assessment 2015: Human Health in the Arctic. Arctic Monitoring and Assessment Programme (AMAP), 2015Google Scholar,13AMAP Assessment 2021: Mercury in the Arctic. AMAP.https://www.amap.no/documents/doc/amap-assessment-2021-mercury-in-the-arctic/3581Google Scholar,14AMAP Assessment 2021: Human Health in the Arctic. AMAP.https://www.amap.no/documents/doc/amap-assessment-2021-human-health-in-the-arctic/3593Google Scholar,15AMAP Assessment 2011: Mercury in the Arctic. 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Palgrave Macmillan, 2017: 101-120Crossref Scopus (3) Google Scholar However, there is a need for additional scientific information to inform policy making aimed at further protecting people from adverse effects of mercury exposure. Despite an increasing scientific and societal realization that mercury pollution is linked to a broad range of sustainability issues,30Sharma B.M. Bharat G.K. Šebková K. Scheringer M. Implementation of the Minamata Convention to manage mercury pollution in India: challenges and opportunities.Environ. Sci. Eur. 2019; 31: 96https://doi.org/10.1186/s12302-019-0280-3Crossref Scopus (7) Google Scholar,33Selin H. Selin N. The human-technical-environmental systems framework for sustainability analysis.Sustain Sci. 2022; https://doi.org/10.1007/s11625-022-01177-0Crossref Scopus (1) Google Scholar,34Selin H. Selin N.E. Mercury Stories: Understanding Sustainability through a Volatile Element. MIT Press, 2020Crossref Google Scholar a more comprehensive understanding of mercury pollution as a sustainability governance challenge is needed.In this review—50 years after the United Nations Conference on the Human Environment in Stockholm and 5 years after the entry into force of the Minamata Convention—we examine connections between major aspects of the mercury issue and the global sustainable development agenda, over a centruy-long time frame (1972–2072). The analysis focuses on mercury discharges from the two largest sources globally: coal-fired power plants and the ASGM sector. We draw from a literature review of international reports, synthesis articles, and a large number of natural and social sciences articles focusing on mercury and coal burning and ASGM, respectively. We highlight four points related to mercury science and governance in the context of sustainability. First, 50-year trends in mercury production, use, emissions, and releases are uncertain and mixed, but national and international efforts addressing mercury-related environmental and human health problems have increased in scope and stringency. Second, over the past 50 years, coal burning and ASGM have become increasingly linked to sustainability challenges due to complex production and consumption patterns and an expansion of international policy. Third, a global indicator of total cumulative anthropogenic discharges can provide useful information on the status of the mercury problem for global policy making, but such an indicator cannot provide sufficient insight on mercury’s localized impacts on human well-being. Fourth, looking forward, many necessary long-term interventions to address mercury pollution are connected with broader policy debates and actions on sustainability transitions.Global mercury trends since 1972The human fingerprint on mercury’s global biogeochemical cycle has been summarized in prior literature and assessments, which largely focus on human-induced mercury emissions to the atmosphere, atmospheric transport, and deposition to ecosystems where methylmercury is formed in aquatic environments. To review the mercury pollution problem and how it has changed since 1972, we take a broader approach by synthesizing existing data on global trends in mercury production, consumption, and anthropogenic emissions and releases in the context of sustainable development. Consistent with Minamata Convention language, we use the term emissions to mean mercury emissions to the air, releases refer to mercury releases to land and water, and discharges include both emissions and releases of mercury. Related to our first point, while total primary mercury mining has declined and mercury uses in products and industrial manufacturing processes have been reduced over the past five decades, estimates of global emissions trends provide conflicting data, and the one estimate of global releases indicates no change. Taken together, these estimates provide a mixed overall picture of how global mercury pollution has changed since the Stockholm Conference. At the same time, policy interventions to address mercury pollution have expanded dramatically, including under the Minamata Convention.Mercury is emitted and released to the environment both by natural processes (such as volcanic eruptions and weathering of rocks) and by anthropogenic activities. The human contribution is far larger than emissions and releases from natural processes.20Obrist D. Kirk J.L. Zhang L. Sunderland E.M. Jiskra M. Selin N.E. A review of global environmental mercury processes in response to human and natural perturbations: changes of emissions, climate, and land use.Ambio. 2018; 47: 116-140https://doi.org/10.1007/s13280-017-1004-9Crossref PubMed Scopus (336) Google Scholar Human activities mobilize mercury through mining of mercury, other mining processes, and the burning of fossil fuels (largely coal) where mercury is a contaminant. Figure 1 shows a summary of available data on global trends over the past 50 years in mercury production (primary mining) and consumption, anthropogenic emissions, anthropogenic releases, and key milestones on global mercury policy and sustainability. Figure 1 also shows available emissions projections over the next 50 years. Both production and consumption of mercury were much higher at the time of the Stockholm Conference than they are today. Over the past five decades, there has been a steep decline in primary mercury mining, which is reflected in Figure 1 in trends in production. Related changes in commercial mercury consumption, including information on fluctuations in mercury prices, are summarized in Box 1. The production, consumption, emissions, and releases of mercury are closely linked to one another through the biogeochemical cycle. Both new mercury discharges and historically emitted legacy mercury are involved in global atmospheric transport and environmental cycling.Box 1Mercury, mining, and uses over the past 50 yearsMercury is a naturally occurring chemical element in the Earth’s crust. It is the only metal in the periodic table that is liquid at room temperature, and different organic and inorganic mercury compounds are found in solid and gaseous forms. Some mercury compounds have been synthesized in laboratories and these can also end up being discharged into the environment.34Selin H. Selin N.E. Mercury Stories: Understanding Sustainability through a Volatile Element. MIT Press, 2020Crossref Google Scholar World mercury production from mining in 1972 was roughly 9,500 Mg, or 279,508 flasks, a unit of measure specifically used for mercury and equivalent to 34 kg.41Cammarota V.A. Mercury.in: Minerals Yearbook: Metals, Minerals, and Fuels. Bureau of Mines, 1972: 771-781Google Scholar This represented about a 10% decrease from the all-time global peak at 298,552 flasks in 1971. Several historically dominant mercury mines have been shut down since the Stockholm Conference, including the ones in Huancavelica, Peru (1974), Idrija, Slovenia (1995), and Almadén, Spain (2002), but mining continued in a few other places, including China (however, mercury mining in Wanshan, going back thousands of years, ended in 2003).42Du B. Li P. Feng X. Qiu G. Zhou J. Maurice L. Mercury exposure in children of the wanshan mercury mining area, guizhou, China.Int. J. Environ. Res. Publ. Health. 2016; 13: E1107Crossref PubMed Scopus (25) Google Scholar Much commercial mercury has been recycled and used in multiple manufacturing processes and products over time as well as traded internationally.43United Nations Environment ProgrammeGlobal Mercury Supply, Trade and Demand.2017Google ScholarThe international price of mercury has fluctuated substantially over the past 50 years. In 1972, the average price of mercury was $41,175 per Mg (in year 2021 US dollars), down from a peak price of over $141,000 (year 2021 US dollars) in 1965.44U.S. Geological SurveyMercury Statistics. U.S. Geological Survey, 2014Google Scholar The mercury price declined until the early 2000s, then increased again to a peak value of about $115,000 per Mg (in year 2021 US dollars) in 2013.44U.S. Geological SurveyMercury Statistics. U.S. Geological Survey, 2014Google Scholar This more recent price increase was largely due to a growing demand for mercury for use in the expanding ASGM sector even as some countries restrict mercury import and use in ASGM.43United Nations Environment ProgrammeGlobal Mercury Supply, Trade and Demand.2017Google Scholar The mercury price declined again after 2013, but illegal extraction in previously closed mercury mines in Mexico and Indonesia together with undocumented exports provided increased supply internationally.43United Nations Environment ProgrammeGlobal Mercury Supply, Trade and Demand.2017Google Scholar Because the United States and the European Union adopted mercury export bans starting in the 2000s, and a growing number of other countries also introduced export and import restrictions, there is no longer a global commercial commodity price for mercury, but prices vary across regional and domestic markets based on demands and controls.34Selin H. Selin N.E. Mercury Stories: Understanding Sustainability through a Volatile Element. MIT Press, 2020Crossref Google Scholar Some places, including Hong Kong and the United Arab Emirates, continue to be important nodes in the international mercury trade.43United Nations Environment ProgrammeGlobal Mercury Supply, Trade and Demand.2017Google ScholarGlobal mercury use peaked around 1970, about the same time as primary mercury mining hit an all-time high, at near 10,000 Mg per year.36Horowitz H.M. Jacob D.J. Amos H.M. Streets D.G. Sunderland E.M. Historical mercury releases from commercial products: global environmental implications.Environ. Sci. Technol. 2014; 48: 10242-10250https://doi.org/10.1021/es501337jCrossref PubMed Scopus (185) Google Scholar Many industrial uses of mercury expanded during much of the twentieth century, but global demand began to decline around the time of the Stockholm Conference. Mercury in 1972 was used in a variety of consumer products (including electronic goods, thermometers and other measuring and control devices, batteries, and paints) as well as multiple chemical manufacturing processes, including chlorine and caustic soda production.41Cammarota V.A. Mercury.in: Minerals Yearbook: Metals, Minerals, and Fuels. Bureau of Mines, 1972: 771-781Google Scholar Mercury was also frequently used in dental amalgam. Roughly two-thirds of global mercury consumption in the early 1970s was in industrialized countries.36Horowitz H.M. Jacob D.J. Amos H.M. Streets D.G. Sunderland E.M. Historical mercury releases from commercial products: global environmental implications.Environ. Sci. 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