Mercury still subtly hazardous

In the 1950s, the Japanese fishing village of Minamata was hit by an inexplicable outbreak of health problems-from vision loss and paralysis in adults to physical deformities and cerebral palsy in newborn babies.

The cause of the villagers’ mysterious symptoms was eventually traced to mercury poisoning. The villagers had unknowingly received exceptionally high doses of mercury through fish they ate from Minamata Bay, where a chemical plant had been dumping the pollutant for years. The experience revealed for the first time that mercury can move up the food chain to people. 

More than 50 years later, mercury-contaminated fish remain a human health issue. Fish consumption, in fact, is the primary way people are exposed to mercury, although most such exposures are at considerably lower levels than those of Minamata and generally have more subtle effects.

Mobile Mercury

Mercury is naturally present in the Earth’s crust, but gets released into the environment through human and natural activities. About half of the estimated 8.5 million pounds of mercury released into the atmosphere in 2005 came from human activities-primarily coal burning-while the other half came from natural sources like volcanoes, according to the United Nations Environment Programme. In Wisconsin, coal-fired power plants and a chloro-alkali plant are the main sources of mercury emissions, said James Hurley, a mercury expert at the University of Wisconsin Sea Grant Institute.

Mercury in the atmosphere eventually falls back to Earth in dry form or in precipitation-sometimes landing close to its emitting source, sometimes landing thousands of miles away. When mercury is deposited in water bodies, bacteria convert it to more toxic methylmercury, an organic form of mercury that accumulates easily in tissues. Wisconsin’s smaller, inland lakes generally have higher concentrations of methylmercury than Lake Michigan, said Hurley. This form of mercury is taken up by tiny aquatic plants and animals and continues up the food chain, becoming more concentrated at each step. Concentrations in large fish at the top of the food chain can be over a million-fold higher than in the surrounding water.

People who eat contaminated fish frequently or eat heavily contaminated fish may accumulate enough mercury in their own bodies to experience health problems, primarily of the nervous system. The U.S. Environmental Protection Agency (EPA) considers blood mercury levels of 5.8 parts per billion or more potentially unsafe. (Reported levels of Minamata villagers were 10 to 150 times higher.) An estimated 437,000 Wisconsin adults have levels above this threshold, according to EPA.

Developing fetuses are especially sensitive to mercury. At UW-Milwaukee (UWM), researchers have been studying the effects of mercury in zebrafish as a surrogate for humans. They found that zebrafish hatched from eggs exposed to 0.01 parts per billion of mercury in the first 24 hours after fertilization had vision and learning problems as adults. “They never recovered-that’s the scary part of all this,” said Daniel Weber, a scientist at UWM’s Children’s Environmental Health Sciences Core Center. A study of the impact of similar lifelong health effects in people estimated that losses in IQ due to fetal exposure to manmade mercury emissions result in reductions in productivity that cost the United States $8.7 billion annually.

Choosing Fish Wisely

Nearly all fish contain trace amounts of mercury, according to EPA. Yet fish is an excellent source of low-fat protein and, in some cultures, a staple source of nutrients. Certain fish species are also high in beneficial omega-3 fats, considered important to fetal development. Experts recommend people maximize the benefits of fish while minimizing risks from mercury (and other contaminants like PCBs) by following advisories for commercial and locally caught fish (see sidebar).

In general, people should pay attention to the size, species, and source of fish they eat, said UWM health scientist John Dellinger, who collaborated on the zebrafish study. The least contaminated fish are typically smaller, non-fish eating species from cleaner water bodies.

Cutting Emissions

Many experts point out that while fish advisories are useful if followed, the ultimate way to reduce mercury’s impact on human health is to cut emissions. “There are lots of industrial processes that use mercury that need to be more efficient,” said Michael Carvan, a UWM Great Lakes WATER Institute scientist and zebrafish study collaborator. “There are coal-fired power plants that need to stop emitting mercury. That means putting some really effective technologies out there.”

Added Hurley, “If you significantly reduce atmospheric emissions, you’d see a pretty rapid [mercury decrease] in fish.” Measurable decreases can occur within less than a year after emissions are reduced, according to the DNR.

Last year, Wisconsin enacted a rule requiring coal-fired power plants to reduce their mercury emissions by 90 percent by 2015, or by 2021 if they agree to more stringent standards for other pollutants.

We Energies, which operates five coal-fired plants, is pursuing the latter option. The company has had a mercury reduction research program in place since the late 1990s, said We Energies environmental scientist David Michaud, and currently captures from 10 to 80 percent of its mercury, depending on the type of coal and technologies used at a particular plant. A recent $53 million mercury-control demonstration project at We Energies’ Presque Isle plant in Marquette, Mich., which uses a fabric filter and sorbent injection, has so far been achieving about 90 percent capture, he said.

Jennifer Yauck is a science writer at the Great Lakes WATER Institute. GLWI (glwi.uwm.edu) is the largest academic freshwater research facility on the Great Lakes.

Emission Sources

According to the DNR, 4,140 pounds of mercury was released into the air from permitted Wisconsin facilities in 2005. Of that total, 2,586 pounds (62.5%) came from coal-fired power plants and 1,139 pounds from the chloro-alkali facility in Port Edwards, Wis. (which plans to eliminate its mercury cell technology by the end of this year). Source: dnr.wi.gov/news/mediakits/mk_mercury.asp.

For data on Milwaukee-area mercury sources, see epa.gov/glnpo/bnsdocs/milwaukeehg/summary.html.

Fish Advisory Information

• EPA/FDA federal advisory for commercial and locally caught fish - epa.gov/waterscience/fish/advice
• DNR state advisories for locally caught fish - dnr.wi.gov/fish/consumption
• Great Lake Indian Fish and Wildlife Commission tribal advisories for locally caught fish - glifwc.org/biology/inlandfish/mercury/mercury.html