Fishing boat in Ilulissat, Greenland, 2 July 2008. Greenlanders are highly exposed to mercury because their diet is almost completely reliant on contaminated marine life. Photo: Kristine Riskær / flickr

By Brian Bienkowski, Environmental Health News
18 January 2013

(Scientific American) – As United Nations delegates end their mercury treaty talks today, scientists warn that ongoing emissions are more of a threat to food webs than the mercury already in the environment.

At the same time, climate change is likely to alter food webs and patterns of mercury transport in places such as the Arctic, which will further complicate efforts to keep the contaminant out of people and their food.

University of Wisconsin researchers recently found that mercury added to a lake reached top predators faster than the mercury that already existed in their environment.

“It was amazing how fast the mercury got into the fish,” said James Hurley, project researcher and director of the university’s Water Resources Institute in Madison.

And this was no lab experiment – researchers put mercury into Lake 658, part of the Experimental Lakes area in Ontario, Canada. Over a year, they put about three times the amount normally received through rainfall and nearby wetlands.

For mercury to show up in top lake predators, it has to be converted to methylmercury – mercury’s toxic form -- by organisms. Then it has to move up through the food web. 

At Lake 658, this happened within months.

“We started seeing the isotope we added in June accumulate in yellow perch by early fall,” Hurley said. “By the start of the second year, we were clearly seeing it even in predatory fish.”

Before this study, researchers didn’t have any idea about how long it took for mercury to move through the environment, said David Krabbenhoft, a research hydrologist with the U.S. Geological Survey’s Wisconsin Water Science Center.

Once researchers stopped adding mercury, the concentrations in fish dropped quickly.

The discovery that new mercury seems to be more of a threat than old mercury could add impetus for reducing global emissions. Critics of mercury rules often say that because mercury is an element that recirculates, new emissions have minimal impact compared with historic and natural ones.

The United Nations today adjourns a meeting in Geneva where governments of about 130 nations have been debating a mercury reduction treaty.

Asia is by far the largest source of new mercury emissions, and coal-burning power plants are the top contributor. Small-scale gold production and residential heating from other fossil fuels are other major sources.

Exposure to high levels of mercury, often from consumption of fish and other seafood, can damage developing brains, reducing children’s IQs. It also has been linked to cardiovascular effects in some adults and children.

The UN released a report leading up to the conference that showed the amount of mercury in the world’s oceans has doubled in the past century. [more]

Mercury Emissions Threaten Aquatic Environments

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