Fall 2007


Mercury threatens wildlife like loons as well as people who eat certain types of fish. A new study published in the Proceedings of the National Academy of Sciences offers good news for reducing levels of mercury in aquatic environments.
Photo: Michelle P. Woodford
UW Water Resources Research

Mercury Accrues, Declines in Fish Quickly

By Kathleen Schmitt Kline

A landmark study recently published by an international team of scientists has found that cracking down on air pollution will provide healthier fish for the dinner table.

“This is the first time that we have been able to use techniques that could show that addition of new mercury to a lake directly increased the mercury level in its fish” said James Hurley, assistant director for research and outreach at the UW Aquatic Sciences Center and one of the study’s 24 authors.

Mercury is a powerful neurotoxin that can cause serious health problems, especially in developing fetuses and young children. When airborne mercury lands in lakes and other bodies of water, bacteria transform it to methylmercury, an organic form that accumulates in fish.

This ongoing study uses a remote lake in Canada to track how mercury moves through an ecosystem. The key to the project was adding minute amounts of stable mercury isotopes — which differ only in atomic configuration — directly to the lake and sprayed over the surrounding watershed. These isotopes allowed researchers to track both the source and the timing of methylmercury formation and accumulation in fish.

The potency of mercury has led to countless fish advisories around the nation, and, in response, a growing demand for action. Much of this attention has been focused on coal-burning power plants — the main source of mercury pollution today in the United States.

But there is “old” mercury in the environment as well. It’s been emitted into the air since the industrial revolution and used in everything from dental fillings to kids’ sneakers.

With so much of this “old” mercury already in the environment, policymakers have debated whether spending billions of dollars to reduce air emissions will actually make fish healthier and people safer.

The results of the study finally provide an answer.

Researchers found that methylmercury levels in fish increased during the first three years of the study and that essentially all of the increase came from mercury deposited directly to the lake surface. That, they said, means methylmercury in fish should decrease quickly if mercury deposition is reduced.

“We can say conclusively that if you reduce mercury emissions it will result in less mercury in fish,” said study co-author Vincent St. Louis of the University of Alberta.

Wisconsin’s portion of the study was funded by the National Institute for Water Resources, Electric Power Research Institute, Wisconsin Department of Natural Resources, and Wisconsin Focus on Energy.









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