Researchers at China’s Nanjing University analyzed the global flows of mercury and found that almost half of the exposure to the toxic metal comes from mercury embedded in global trade.
In a paper published in the journal PNAS Nexus, Zhencheng Xing and co-authors explain that the world emits about 1,800 megagrams of mercury annually. Most of these global emissions are linked to the smelting and pressing of non-ferrous metals, particularly during artisanal and small-scale gold mining.
Mercury used in these processes can wash downstream and become airborne, polluting soil, rivers and parts of the ocean. People are then exposed through eating seafood, freshwater fish, or rice—sometimes many thousands of miles away from the mercury’s source.
“Forty-seven-per-cent of global Hg emissions are related to commodities consumed outside of the countries where the emissions are produced, which has largely influenced the environmental Hg levels and human exposure thereto across the world,” the paper reads.
Many developed countries, including the United States and Japan, can be classified as outsourcers of mercury because they are the ultimate consumers of gold, electric equipment, machinery, and other products whose manufacturing generates mercury pollution, but such countries are spared from exposure.
According to the authors, strategies to tackle mercury exposure should include both production-side controls and demand-side measures, including consumption taxes to influence consumer behaviour.
“Through investigation of a longer chain of the global biogeochemical Hg cycle from economic production to human health, international cooperation on Hg control strategies in the Minamata Convention can be facilitated,” the authors point out.
To reach these conclusions, Zhencheng’s team traced the element through international trade routes from sites of pollution to exposure in the environment and accounted for the resulting human health impacts. The scientists then linked a mercury emission inventory, a global multi-regional input-output model, a coupled atmosphere-land-ocean-ecosystem model, and an exposure-risk-valuation model to investigate the global biogeochemical mercury cycle.