Edwin L. Aguirre
In a study published this month in the journal Nature
, Obrist’s team found that the absorption of mercury from the atmosphere by the tundra is shown to drive high loads of mercury in Arctic tundra soils. Tundras are vast, treeless regions where the soils are permanently frozen, or “permafrost.” Mercury runoff from tundra soil then supplies 65 to 85 tons of the toxic heavy metal to Arctic lakes, rivers and the Arctic Ocean each year.
“This mercury from the tundra soil explains half to two-thirds of the total mercury input to the Arctic Ocean,” says Obrist.
Obrist recently led an international group — including researchers from UMass Lowell, the Desert Research Institute in Reno, Nev., Paris-Sorbonne University and the University of Toulouse in France, the University of Colorado and the Gas Technology Institute in Des Plaines, Ill. — to conduct a long-term study of the origin of mercury pollution in the Arctic tundra. The investigation was supported by the U.S. National Science Foundation.
“This is the most comprehensive study ever done on mercury deposition,” notes Obrist.
A Highly Neurotoxic Pollutant
Mercury is one of the most harmful pollutants threatening fish, birds and mammals worldwide. Hundreds of tons of it are released into the atmosphere each year by power plants through the burning of coal, as well as through mining activities and other industrial processes, and are distributed throughout the world. Airborne mercury eventually falls back to the ground, accumulating in soils, rivers, lakes and oceans.
A first global treaty, the Minamata Convention
that aims to protect human health and the environment from the adverse effects of mercury, was adopted in 2013. It has been signed by 128 member countries — including the U.S. — and will take effect in August of this year.
“Mercury is a neurotoxic pollutant that has led to high exposure levels in northern wildlife, such as beluga whales, polar bears, seals, fish, eagles and other seabirds,” says Obrist. “It also affects human populations, particularly the Inuit, which rely on traditional hunting and fishing.”
Exposure to high levels of mercury over long periods can lead to neurological and cardiovascular problems. Infants and young children can suffer from developmental disorders, reduced memory performance and increased risk of attention problems.
Mercury exists in several forms, including methylmercury and other organic compounds, elemental (metallic) mercury and inorganic mercury compounds.
“We determined the dominant source of mercury in the Arctic tundra to be the gaseous form of elemental mercury that is being transported in the atmosphere,” says Obrist. “During a span of two years, we developed a complete accounting of all atmospheric mercury inputs and an inventory of soil mercury deposits at our observation site, which is in an inland tundra in northern Alaska north of the Brooks Range. We used a unique combination of different techniques that allowed us to make precise measurements for two full years, including through the Arctic winter.”
The scientists found that 70 percent of atmospheric mercury deposition is driven by the gaseous elemental form, whose deposition is normally not measured and travels the farthest distances in the atmosphere so it easily reaches the Arctic. In contrast, deposition via rain and snow, which generally is the focus in most studies, is very small over the northern Arctic tundra — approximately 2 percent of the total mercury deposition.
How does gaseous elemental mercury end up in the tundra soil?
“It’s a process similar to the uptake of carbon dioxide by plants. In this case, the mercury gas is absorbed by tundra plants and then transferred to the soil when the plants shed leaves or die off,” explains Obrist. As a result, the Arctic tundra becomes a significant deposit for mercury emitted from industrialized, more southern regions of the world.
“We calculate that large amounts of mercury are trapped in tundra soils, possibly up to a third to one-half of the world’s total soil mercury deposits. These deposits may be critically threatened by an unprecedented Arctic climate warming that could destabilize Arctic soils and possibly lead to more mercury being released into streams, rivers, lakes and the Arctic Ocean. This would further harm the welfare of Arctic wildlife and people,” adds Obrist.