IN 2005, the Environmental Protection Agency took its first important step toward reducing mercury pollution from coal-fired power plants. Its Clear Air Mercury Rule is intended to bring about a 70 percent reduction in mercury emissions over the next 20 years.
But the new rule does not require all plants to reduce emissions by the same amount. Some may be allowed to pollute more than others by buying pollution credits from other plants.
The E.P.A.’s faith in this “cap and trade” approach is based on the assumption that mercury pollution disperses evenly in the environment. This strategy has worked well in reducing emissions of sulfur dioxide, a component of acid rain. But mercury does not behave in the same way as acid rain. In fact, much of the mercury emitted by coal-fired power plants remains near those plants.
In a just completed 10-year study of birds, fish and mammals in the northeastern United States and southeastern Canada, we found five places where fish and wildlife have exceptionally high concentrations of mercury in their blood. Under the E.P.A.’s new rule, these biological mercury “hot spots” could persist, with dangerous consequences for the health of people and wildlife.
For more than a century, mercury pollution has blanketed much of the United States. Coal-fired power plants and other sources emit mercury into the atmosphere, where it is carried with the wind and deposited onto the ground. On land, particularly in wetlands, mercury can change to a form known as methyl mercury, which readily accumulates in organisms.
Methyl mercury is taken up by microscopic plants and animals, which are then consumed by fish and other animals. As it moves up the food chain, methyl mercury increases in concentration as much as 10 million times. Animals at the top of the chain that consume lots of tainted fish — common loons, bald eagles, river otters and some humans — are exposed to methyl mercury in amounts high enough to cause neurological damage, behavioral abnormalities and reproductive problems.
Children are particularly at risk for mercury poisoning. Some 200,000 to 400,000 children born in the United States each year have been exposed to mercury levels in their mothers’ wombs high enough to impair neurological development, according to an analysis of data gathered from 1999-2002 by the National Health and Nutrition Examination Survey.
David C. Evers is the executive director of the BioDiversity Research Institute, in Gorham, Me., and Charles T. Driscoll Jr. is a professor of environmental systems engineering at Syracuse University.