Harvard study finds circumpolar rivers most responsible for high levels of mercury in the Arctic

For immediate release: Monday, May 21, 2012

Boston, MA — Environmental scientists at Harvard have discovered that the Arctic accumulation of mercury, a toxic element, is caused by both atmospheric forces and the flow of circumpolar rivers that carry the element north into the Arctic Ocean.

While the atmospheric source was previously recognized, it now appears that twice as much mercury actually comes from the rivers.

The revelation implies that concentrations of the toxin may further increase as climate change continues to modify the region’s hydrological cycle and release mercury from warming Arctic soils.

“The Arctic is a unique environment because it’s so remote from most anthropogenic (human-influenced) sources of mercury, yet we know that the concentrations of mercury in Arctic marine mammals are among the highest in the world,” says lead author Jenny A. Fisher, a postdoctoral fellow in Harvard’s Atmospheric Chemistry Modeling Group and the Department of Earth and Planetary Sciences (EPS). “This is dangerous to both marine life and humans. The question from a scientific standpoint is, where does that mercury come from?”

The results of the study, which was led jointly by Harvard School of Engineering and Applied Sciences (SEAS) and Harvard School of Public Health (HSPH), have been published in the journal Nature Geoscience on May 20.

Mercury is a naturally occurring element that has been enriched in the environment by human activities such as coal combustion and mining. When converted to methylmercury by microbial processes in the ocean, it can accumulate in fish and wildlife at concentrations up to a million times higher than the levels found in the environment.

“In humans, mercury is a potent neurotoxin,” explains co-principal investigator [[Elsie Sunderland]], Mark and Catherine Winkler Assistant Professor of Aquatic Science at HSPH. “It can cause long-term developmental delays in exposed children and impair cardiovascular health in adults.”

Mercury is considered a persistent bioaccumulative toxin because it remains in the environment without breaking down; as it travels up the food chain, from plankton to fish, to marine mammals and humans, it becomes more concentrated and more dangerous.

“Indigenous people in the Arctic are particularly susceptible to the effects of methylmercury exposure because they consume large amounts of fish and marine mammals as part of their traditional diet,” Sunderland says. “Understanding the sources of mercury to the Arctic Ocean and how these levels are expected to change in the future is therefore key to protecting the health of northern populations.”

Sunderland supervised the study with Daniel Jacob, Vasco McCoy Family Professor of Atmospheric Chemistry and Environmental Engineering at SEAS, where Sunderland is also an affiliate.

Mercury enters the Earth’s atmosphere through emissions from coal combustion, waste incineration, and mining. Once airborne, it can drift in the atmosphere for up to a year, until chemical processes make it soluble and it falls back to the ground in rain or snow. This deposition is spread worldwide, and much of the mercury deposited to Arctic snow and ice is re-emitted to the atmosphere, which limits the impact on the Arctic Ocean.

“That’s why these river sources are so important,” says Fisher. “The mercury is going straight into the ocean.”

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