The hotspots are believed to result from complex processes that move atmospherically released mercury through the environment, and from site-specific characteristics such as the high sensitivity of wetlands and forested areas to mercury inputs. Local sources of mercury are also significant. Although mercury is not directly harmful at ambient levels, it is concentrated up to a millionfold and chemically modified in aquatic food chains, resulting in dangerous levels of methylmercury in some wildlife species. Fish consumption advisories responding to mercury contamination exist in all the states and provinces included in the study, and loons are adversely affected by mercury levels they experience.
The hotspots have implications for "cap and trade" approaches being implemented for regulation of emissions from coal-fired electric power stations, which, along with municipal waste incinerators, are major sources of mercury pollution. Cap and trade approaches seek to reduce the total release of mercury but could lead to static or increased emissions in some areas. Greater deposition of mercury near areas that are highly sensitive to the element or that are already affected by it could raise the risk to people and wildlife that consume fish. There is reason to believe, however, that lo wering emissions can reduce risk: an analysis of levels of mercury contamination over time in the Merrimack River watershed suggests that lowered emissions reduced mercury levels in biota within a few years.
The 10-member research team was led by David C. Evers of the BioDiversity Research Institute in Gorham, Maine. The study was based on samples collected over four years by the Northeastern Ecosystem Research Cooperative and made use of 7311 observations for seven species. The study report in BioScience is accompanied by an overview article, written by Charles T. Driscoll of Syracuse University and colleagues, that summarizes current knowledge about mercury contamination in the region; the authors conclude that reductions in mercury emissions beyond those currently under way will be needed to eliminate the element as a health risk to humans or to populations of loons.