Mercury pollution from the early days of coal burning and gold mining is still poisoning Arctic wildlife more than a century later, according to a new study in Nature Communications.
Despite global efforts to curb emissions, mercury levels in top predators like polar bears and toothed whales remain dangerously high, and researchers say the culprit is legacy pollution making its way to the Arctic via ocean currents.
A team of scientists analysed over 700 samples collected across Greenland over the past 40 years, from animal tissues to peat in the ground. By examining the chemical “fingerprint” of Mercury isotopes, they found that Mercury concentrations have not fallen – and in some cases are still rising – in Arctic ecosystems.
“This helps explain the lack of decline in Arctic mercury levels,” Prof Rune Dietz, one of the study’s co-authors, said in a statement. “Transport of mercury from major sources like China to Greenland via ocean currents can take up to 150 years.”
Mercury released into the air from human activities can circle the globe for about a year before falling to Earth. But once it enters the ocean, it can persist for centuries, slowly travelling north via deep, cold currents.
Central West Greenland, for instance, is influenced by Atlantic inflow via the Irminger Current in the North Atlantic, while other regions receive mercury-laden water from the Arctic Ocean currents.
In polar bears and toothed whales, mercury concentrations are now 20 to 30 times higher than pre-industrial levels.
“We have not seen any proof of actual kills of top predators,” Dietz told BBC Science Focus in an email, “but the loads in toothed whales and polar bears, as well as the Inuit populations in the highest exposed areas, are high enough to show neurological effects.”
Mercury is a potent neurotoxin that can also damage the immune system and reproductive health. So harmful is the naturally occurring element that the World Health Organization lists it as “one of the top ten chemicals of major public health concern”.
The findings carry serious implications for the UN Minamata Convention, a global agreement aimed at reducing mercury pollution. While cutting emissions remains essential, the study suggests it may take generations for the Arctic to recover.
The team plans to continue investigating mercury’s impact on the fragile Arctic ecosystem. Dietz says that modelling how long it takes mercury to travel from major emitters like China to different Arctic regions could be key to understanding – and eventually confronting – the long-term threat.
Read more:
- What are the 10 coldest places on Earth?
- Polar bears aren't actually white. Here's why
- Do all fish and shellfish contain mercury?
About our expert
Rune Dietz is a professor in the Department of Ecoscience at Aarhus University. His research has been published in peer-reviewed journals including Environmental Research, Molecular Ecology, and Ecology and Evolution.