Mercury and Health

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Science  27 Sep 2013:
Vol. 341, Issue 6153, pp. 1430
DOI: 10.1126/science.1245924

This October, nations will gather in Japan to sign the Minamata convention, a treaty to address the toxic effects of mercury in the environment. The agreement will become binding once ratified by at least 50 nations. The convention is timely and welcome in that it places controls and limitations on products, processes, and industries that increase the level of exposure of people and the environment to mercury, a naturally occurring element. Mercury bioaccumulates in the form of methylmercury, a powerful neurotoxin that can affect wildlife, domestic animals, and humans alike. Symptoms of mercury poisoning can range from numbness in the hands and feet and muscle weakness in mild cases, to insanity and death.

This convention is named after the Japanese city where the release of methlymercury in the wastewater from a chemical factory from 1932 to 1968 polluted the local seafood, which then caused severe mercury poisoning in thousands of local residents dependent on that resource. Minamata was a case where science provided the evidence connecting the cause (effluent discharge) with the effect (neurologically diseased patients). Seafloor sediment samples recovered from the bay offshore of Minamata showed that the concentration of methylmercury contamination was highest near the industrial outflow to the ocean and decreased from there. Samples of local seafood and shellfish were laden with mercury. Hair samples from the afflicted population showed highly toxic amounts of the element. Local cats, consumers of the scrap seafood from their owners' tables, were the first to die. Ultimately, the industrial discharge ceased, and the responsible party was ordered to compensate the victims.


Critics of the Minamata Convention believe that it does not go far enough. For example, in 2010 the top two sources of mercury pollution were artisanal gold mining (727 tons) and coal-fired power plants (475 tons).* As many as 15 million adults and children live in communities at risk from mercury pollution from artisanal gold mining, primarily in Africa and South America. Mercury from coal-fired power plants can be transported through the atmosphere far from the source, deposited in aquatic systems, and then converted to methylmercury. The population at risk may have had no voice in the decision to install the coal-fired facility. The treaty stops short of specifying goals or target dates for action plans for reducing mercury release from mining, nor does it require refitting of existing coal-fired power plants to reduce mercury emissions.

One roadblock standing in the way of stronger controls on mercury in the environment, better national action plans, and perhaps even swifter ratification of the Minamata Convention is that many environmental and health aspects of mercury are poorly known, except in the most acute cases of mercury poisoning. Science can help by linking research on mercury's behavior in the environment (see the Perspective by Krabbenhoft and Sunderland on p. 1457) with studies of its public health impacts. Research teams need to include environmental toxicologists who understand the biochemistry of toxic contaminants, ecologists who trace their bioaccumulation through the food chain, physicians who understand the effects of chronic and acute exposure on long-lived species such as us, and public health specialists who can extract patterns from large populations. What geographic areas are most at risk? Which population demographics are particularly vulnerable? What symptoms should we look for? What other factors might confound their identification? Even at sublethal levels, does exposure to mercury have impacts on the development of young children? Is there a level of mercury consumption that is perfectly safe?

Such investigations cross the boundaries of government agencies and of university schools and departments. Funding the many investigators could be a challenge. But with the number of coal-fired power plants projected to rise globally, tracing the connections between mercury pollution and health must be a priority.

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