Mercury, a poison that resists disappearing from the planet

BarcelonaIn the fifties, Japan was the scene of an industrial pollution catastrophe. A factory belonging to the company Chisso [now JNC] dumped wastewater containing methylmercury into the sea, a highly toxic compound that accumulated in the fish and seafood that the population then consumed. In 1956, Minamata disease was identified, which caused irreversible neurological damage. In some cases, those affected were babies, because their mothers had been exposed during pregnancy. Among them was Tomoko Uemura, who died at 21 and became the symbol of this tragedy. Seven decades later, and in different parts of the world, this poison for living beings continues to exist and now a study published in Science warns that it hides risks for ecosystems and human health: the climate crisis could favor the mobilization of mercury accumulated over centuries.

Thousands of years ago, unintentional releases of mercury began during the refining of ancient metals and, from the mid-18th century onwards, emissions increased on an industrial scale due to metal exploitation and combustion. Although emissions have since been significantly reduced in much of the world, this toxin does not disappear. Vegetation, for example, captures mercury from the air and transfers it to the soil, which can store it for centuries. This means that today there is a large amount in the soil, waters, and oceans, from where it can return to circulate around the planet. Furthermore, mercury salts have historically been used as industrial catalysts in chemical plants, which also generated methylmercury as a byproduct.

The authors of the article, researchers from the Spanish National Research Council (CSIC) Aryeh Feinberg and Alfonso Saiz-Lopez, estimate that approximately 30% of current mercury emissions come directly from human activities, while about 60% corresponds to ancient mercury that re-volatilizes from terrestrial and oceanic surfaces. The remaining 10% has a geological origin. The scientists underline that global warming, fires, and melting ice can not only alter its cycle, but also favor its transformation into more toxic forms. “Ancient mercury continues to circulate through the ocean-land-atmosphere system, creating a complex recycling loop that can trap the toxic element in the biosphere for centuries,” the experts warn.

Industrial changes and vulnerable communities

But the concern is not only environmental: experts warn that, under certain conditions, microorganisms in aquatic ecosystems can transform it into methylmercury and advance through the food chain. For this reason, large aquatic predators and people can be exposed to significant amounts of the contaminant, as happened in Japan in the fifties. In 2013, half a century after the Japanese catastrophe, the United Nations signed the Minamata Convention to set measures to protect human health and the environment, among which were limits on mercury emissions from power plants and industrial facilities and the elimination of primary mercury mining activities and the uses of mercury in chemical processes and consumer products.

These measures have contributed to reducing atmospheric mercury concentrations in Europe and North America since the nineties, and in East Asia since the 2010s. But the consequences of the existence of this toxic substance can be especially relevant in the Arctic and the tropics, regions where the mercury cycle is sensitive to environmental changes and where indigenous communities depend on locally caught marine products as a main source of protein.

Researchers admit that it is not yet known with enough precision to what extent climate change will end up increasing or reducing mercury pollution. "Future studies should focus on determining this," they suggest.