Fall 2005

UW Water Resources Research

The Ultimate Test Tube

Landmark Mercury Pollution Study Sited at Pristine Lake

By Kathleen Schmitt

An intense debate has developed over how to regulate combustion sources of mercury to the atmosphere, including emissions from coal-fired power plants. Expensive emission controls have been proposed, yet it is unclear whether these controls would reduce mercury levels in fish and ultimately people. An international group of researchers is trying to answer this question by performing a unique experiment on a remote lake in Ontario.

The study, named METAALICUS (Mercury Experiment to Assess Atmospheric Loading in Canada and the United States), is currently underway in Canada’s Experimental Lakes Area. Set aside by the Canadian government in 1968 for research, the area of 58 lakes and their watersheds offers scientists unparalleled opportunities to conduct experiments on entire freshwater ecosystems.

At one lake, roughly 80 miles from the U.S. border, researchers are trying to determine whether new mercury entering the environment is more likely to build up in fish than the mercury that has already accumulated in lake sediment and surrounding soils.

“That’s the real key to this study,” says James Hurley, assistant director for research and outreach at the UW Aquatic Sciences Center and one of the study’s 16 investigators. “To predict the effects of decreased mercury emissions, you need to be able to separate the ‘new’ mercury from the ‘old’ mercury.”

To do this, the researchers are adding minute amounts of mercury—about one teaspoon in total—to the lake and its watershed. They have divided the study into three parts, each using a different isotope of mercury. These are stable, non-radioactive forms of the element that have slightly different arrangements of atoms, allowing them to be identified and traced as they move through the environment.

One isotope is applied directly to the lake’s surface, another to the adjacent wetland, and the third is sprayed over an upland forest using a crop duster. The applications began in 2001, following a year of baseline monitoring. The researchers hope to continue adding mercury until the ecosystem reaches a steady state. When additions of the isotope end, they’ll watch to see what happens to mercury levels in the lake’s fish.

The researchers are also hoping to learn more about how inorganic mercury, found in the air, converts to methylmercury, the toxic organic form that fish and humans can accumulate in their bodies.

“If you can figure out the rates of conversion to methylmercury and release to water, you can probably figure out how much mercury will bioaccumulate in fish,” says Hurley. “The goal is to then apply our results on bioaccumulation to different types of environments.”

The study’s findings will be crucial in deciding how much and how quickly to regulate emissions from coal-fired power plants and how soon these measures might lead to less contaminated fish on dinner tables.

Wisconsin’s portion of METAALICUS is funded by the National Institute for Water Resources, Electric Power Research Institute, Wisconsin Department of Natural Resources, and Wisconsin Focus on Energy. For more information about the project, visit www.umanitoba.ca/institutes/fisheries/METAALICUS1.html

The Aquatic Sciences Center is the administrative home of the
University of Wisconsin Sea Grant Institute & University of Wisconsin Water Resources Institute.

©2011 University of Wisconsin Board of Regents