Researchers have discovered dangerous levels of the neurotoxin mercury (Hg) in the muscle tissue of perch and in the blood and eggs of the common loon in aquatic ecosystems of the northeastern U.S. and southern Canada. The finding led them to identify five "hot spots" of mercury contamination that pose serious health risks to animals as well as humans. In addition, elevated concentrations of the neurotoxin were found in nine other regions labeled as "areas of concern" in the report published in the January issue of Bioscience. High concentrations of mercury, which accumulate in the food chain, can cause brain and nerve damage in developing fetuses and young children.

In some areas the team of U.S. and Canadian researchers, led by David Evers of the BioDiversity Research Institute in Gorham, Maine, found perch containing mercury levels as high as 20 times greater than the Environmental Protection Agency's (EPA) recommended limits. A survey of other ecosystem members discovered that 75 percent of bass and trout sampled contained mercury levels exceeding the federal limits.

The northeastern hot spots--which include the western Adirondacks and the middle and lower Merrimack River--share several characteristics: most can track much of their mercury deposition to local sources such as waste incinerators and coal-fired electricity plants. Each area contains landscape components--like tree canopies that suck up airborne mercury particles or wetlands that facilitate the methylation of mercury to the toxic compound methylmercury--that concentrate the pollutant in aquatic environments, sometimes up to one million times greater than its ambient levels. Water manipulation, such as reservoirs, can also ratchet up methylmercury levels, causing a decrease in the viability of wildlife offspring. In addition, soil contamination from legacy mercury use is another major indicator of a hot spot.

"I would say these four factors are likely responsible for biological Hg hot spots in other parts of the country as well," Evers surmises. "The western U.S. and Rockies appear to have major legacy Hg problems that are causing reproductive impairments to birds such as the clapper rail in San Francisco Bay."

The research team predicts its results will affect cap-and-trade regulations implemented by the EPA in 2005 to nudge coal-fired power plants to take steps to reduce their emissions. The cap-and-trade program was designed to encourage the industry to put in pricey pollution controls by allowing them to sell "credits" they received for doing so to other plants. "Trading has the potential to lead to static or increased emissions in some areas of the United States," the authors write in the report, adding that increased deposition in areas with high mercury content will increase contamination in fish and put people who consume that fish at higher risk of mercury poisoning.

Pointing to historical data from the Merrimack River, the authors note that between 1997 and 2002 mercury emissions in southern New Hampshire declined by 45 percent because of regulations on municipal incinerators. As a result, mercury concentrations in loons decreased 64 percent, with an accompanying decline of accumulations in perch.

"The cap-and-trade could work as long as there was an evaluation of landscape sensitivities within a radius of 50 to 100 kilometers of the point source," Evers says. "I think associating monitoring stations as part of the national Hg monitoring network is best and should at least be placed in areas with the greatest risk."

Responding to the new findings, the EPA issued a statement saying that emission reductions made through its Clean Air Interstate Rule will specifically "occur in areas where mercury deposition is currently the highest." The agency insists that it will keep an eye on the situation. "EPA is," says the statement, "working with monitoring, modeling and mercury experts to establish a coordinated, nationwide network of atmospheric mercury monitoring sites."