From 2001 to 2005, BioDiversity Research Institute (BRI) and Environment Canada led a comprehensive effort to compile mercury data from across the northeastern U.S. and eastern Canada. This groundbreaking project produced a database of over 30,000 measurements, mostly from freshwater environments (Figure 1). The results highlight the broad extent and serious effects of mercury across the landscape, the need to expand the view of the problem to include forest ecosystems, the occurrence of biological hotspots in sensitive environments, and the demand for enhanced mercury monitoring.

The BRI effort produced a series of 21 scholarly papers published in a special issue of the journal Ecotoxicology (see page 22). These papers present the most comprehensive understanding of mercury pollution in freshwater ecosystems of northeastern North America. Here the results are condensed into a report that highlights and translates the key findings of these papers for policy makers, the public and others interested in mercury in the environment. This report is organized into five sections: mercury overview; mercury in air, sediments, water and fish; mercury in other wildlife; mercury hotspots; and environmental monitoring. The facts and figures presented in these sections are also summarized in the “Fact Finder” on pages 12 and 13.

Four key messages emerge from this report:

1. A comprehensive analysis of air, water and fish data shows that mercury levels are high and pervasive in northeastern North America. A new map showing model estimates of total mercury deposited on the landscape predicts higher mercury loading to some areas of the Northeast than previously projected (see Figure 4 on page 7). While the map is limited by the lack of mercury monitors in urban areas and near large emissions sources, it shows elevated mercury across the region and particularly high levels in montane forests.

Extensive water and fish data further illustrate the widespread nature of the mercury
problem. Water samples from more than 1,000 locations identified particularly high
mercury in the Adirondack Mountains of New York as well as the Canadian provinces of
Nova Scotia and Newfoundland. The waters with high mercury levels were generally distant from direct point sources and urbanized land use, suggesting airborne mercury is a likely source. However, the data also demonstrate that large sources can have a considerable impact in local areas.

An analysis of fish showed that 15 and 42 percent of the water bodies sampled for brook
trout and yellow perch, respectively, had average fish mercury concentrations exceeding
the U.S. Environmental Protection Agency (EPA) criterion of 0.3 ppm. Moreover, most
species sampled had average regionwide mercury concentrations above this criterion.

2. Until now, most research has focused on mercury in fish and fish-eating birds in
aquatic environments. New research shows that many animals, even forest songbirds, have elevated mercury burdens. Based on these findings, it is increasingly clear that mercury can no longer be viewed as strictly an aquatic pollutant. Conventional thinking holds that mercury is limited to aquatic environments since mercury is most readily converted to its toxic form (methylmercury) in water. However, elevated mercury levels in Bicknell’s thrush and other forest songbirds demonstrate that methylmercury can be produced in terrestrial ecosystems as well. This new finding has implications for the way scientists and policy makers view the nature and extent of mercury in northeastern North America.

Fig. 1. Map of study area and data compiled for analysis

3. Mercury is commonly evaluated as an environmental issue at national and global scales. Yet this approach can overlook small locales with regionally significant mercury pollution. Here, biological hotspots that pose an ecological risk are identified and mapped for the first time in northeastern North America (see Figure 13 on page 20). Hotspots can form in watersheds with high mercury deposition or within highly sensitive ecosystems. In northeastern North America, areas of high mercury loading prevail in upper elevation ecosystems that receive more mercury deposition than surrounding lowlands, as well as areas near large mercury sources. Often however, biological hotspots develop in watersheds where conditions are conducive to methylmercury production or the build-up of mercury in the food chain. This finding illustrates that watershed characteristics can be as important as mercury loading in determining mercury sensitivit y. Moreover, the high mercury levels documented in these biological hotspots suggest the need for stronger mercury standards to protect fish and wildlife (see Box 4 on page 18).

4. Last, it is clear from this analysis that environmental monitoring programs must be expanded in order to fully document the extent and impact of mercury pollution in North America. The current federal monitoring program is limited to the Mercury Deposition Network (MDN). While the 70 existing MDN sites are operating well, they are located primarily in rural areas and are sparsely distributed. They are also limited to collecting mercury in rain and snow. Moreover, connecting air deposition with changes in fish and wildlife is a scientific challenge that must be addressed through an expanded monitoring network. Current programs for measuring water chemistry and fish and wildlife effects are inadequate to detect changing mercury levels and determine ecological effects in a standardized way. A comprehensive system designed to meet mercury monitoring needs nationally is described in a recent paper by Robert Mason and his colleagues entitled, “Monitoring the Response to Changing Mercury Deposition” which appeared in the January 2005 issue of the journal Environmental Science and Technology. Given the changing levels of mercury in the environment, the increasing global pool of mercury and the risk posed to human and ecological health, a collection system for basic information on mercury in the environment should be a high national priority.