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Centuries-old mercury pollution hidden in the ocean threatens Arctic wildlife

Despite global reductions in mercury emissions, mercury concentrations in Arctic wildlife continue to rise. A study in Nature Communications by researchers from Aarhus University and the University of Copenhagen reveals that ocean currents may be transporting legacy mercury pollution to the Arctic—posing a long-term threat to ecosystems and human health.

"We've monitored mercury in Arctic animals for over 40 years. Despite declining global emissions since the 1970s, we see no corresponding decrease in Arctic concentrations—on the contrary," says Professor Rune Dietz from Aarhus University.

Mercury released into the atmosphere from sources like coal combustion and gold mining can remain airborne for about a year. However, once it enters the ocean, it can persist for over 300 years. This means that even with current emission reductions, the Arctic may continue to experience elevated mercury levels for centuries.

Mercury's fingerprint in Arctic wildlife

The researchers analyzed over 700 environmental samples—including tissues from polar bears, seals, fish, and peat—from across Greenland collected over the past 40 years. By examining the composition of six common mercury isotopes, they identified distinct regional differences that align with ocean current patterns.

"These isotope signatures act like fingerprints, revealing the sources and transport pathways of mercury," explains Senior Researcher Jens Søndergaard from Aarhus University.

For example, central West Greenland is influenced by Atlantic inflow via the Irminger Current, while other regions are dominated by Arctic Ocean currents.

Implications for global mercury regulation

Mercury is a potent neurotoxin. In the Arctic, top predators like polar bears and toothed whales, concentrations are now 20–30 times higher than before industrialization. This poses serious health risks not only to wildlife but also to Indigenous communities that rely on marine mammals for food.

"Mercury affects the immune system, reproduction, and possibly sensory functions in animals, which can impact their survival," says Professor Christian Sonne from Aarhus University.

The findings have significant implications for the UN's Minamata Convention on Mercury, which aims to reduce global mercury pollution. The study offers a potential explanation for why mercury levels in Arctic biota remain high despite falling atmospheric emissions.

"Transport of mercury from major sources like China to Greenland via ocean currents can take up to 150 years," says Rune Dietz. "This helps explain the lack of decline in Arctic mercury levels."

The research team is continuing their work on mercury isotopes across the Arctic through the "GreenPath" project. The isotopic analyses also contribute to international projects such as WhaleAdapt and ArcSolutions.