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Local Impact
Study of Mercury Hotspots Reveals Effects of In-Region Sources
by Emma Downs
Given all the environmental issues that require attention, it would be helpful if new research on mercury in our region revealed the problem wasn’t as serious as previous studies have indicated. Unfortunately, the opposite is occurring. In early 2007, the release of a study by a group of prominent researchers pointed to the growing need to address the issue now, before it gets worse—and not to overlook the contributions from mercury sources within our region. As the Northeast Regional Mercury TMDL points out, sources outside our region are having a growing influence on the mercury in our waters. But the impact from in-region sources, while shrinking, remains a serious issue.
Nine scientists from the Hubbard Brook Research Foundation (HBRF) made a new assessment of fish, birds, and mammals in the Northeastern United States and Southeastern Canada and found mercury levels in many areas higher than predicted. They identified five confirmed biological mercury hotspots: the west and central Adirondack Mountains; the Upper Connecticut River; the middle and lower portions of the Merrimack River; the upper portions of the Androscoggin and Kennebec Rivers; and in Canada, Kejimkujik National Park and central Nova Scotia. The researchers also identified nine suspected hotspots, seven of which are in NEIWPCC’s member states.
What Makes a Hotspot Hot
The HBRF scientists define a biological mercury hotspot as a location where mercury concentrations in fish, birds, or mammals exceed established thresholds for human or ecological health compared to the surrounding landscape. Mercury is deposited in a watershed by outside sources and processed by specialized bacteria to become methyl mercury, a form that is more easily absorbed by animals. Hotspots occur when this process happens at an accelerated rate.
Several factors cause this acceleration. One is proximity to large emission sources, as we see in the lower Merrimack River. Also, some watersheds are particularly sensitive to mercury pollution due to the nature of their landscape; acid deposition, low nutrient inputs, forest cover, shoreline wetlands, and forest clearcutting can increase mercury accumulation in an area. Reservoirs with frequent fluctuations in water level are also susceptible to mercury buildup because the continual exposure and rewetting of shore land provides prime conditions for bacteria that produce methyl mercury.
There’s another key point: Because mercury is a fundamental element, it doesn’t break down or degrade, so it can travel long distances. Hence, mercury was long considered a “global” pollutant that travels far from its source. Its effects on its immediate environment were thought to be minimal. Emerging science, however, shows that’s not the case. The reach of mercury’s effects depends on the type of mercury that is present.
Elemental mercury (Hg0) is relatively inert and thus can travel great distances, accounting for mercury’s often noted global effect. This species of mercury makes up half the emissions of mercury from pulp and paper plants and utility oil boilers, 80 percent of the emissions from landfills, and 30 percent of the emissions from coal-fired electric utilities. Reactive gaseous mercury (RGM) is more chemically reactive and thus deposits relatively close to its source. It accounts for 68 percent of mercury emissions from coal-fired electric utilities in the Northeast, and over half the emissions from municipal waste incinerators nationwide. Because of its short range and high rate of production in our region, RGM is the most abundant form of mercury pollution in the Northeast. Particulate mercury (PHg) can travel short to moderate distances. The least common form of mercury emitted, PHg makes up 20 percent of the mercury in discharges from utility oil boilers, municipal waste incinerators, and pulp and paper production.
Conclusions and Considerations
The HBRF study proposes that mercury deposition near large emission sources can be greater than levels previously predicted by national or regional models. Using a computer model designed to capture the impact of local emission sources, the HBRF team found that in an area near Concord, N.H.,in the vicinity of the Merrimack Station coal-fired power plant (see page 3), the local deposition was four to five times higher than EPA’s estimate for the region. The scientists also used the model to generate other conclusions that suggest EPA may have underestimated the impact of coal-fired power plants on mercury deposition in areas near large emission sources.
The study did include some encouraging news. An analysis of monitoring data suggests that as mercury emissions and depositions from local sources decline, mercury levels in fish and wildlife decrease rapidly. For example, between 1997 and 2002, mercury emissions upwind of the hotspot in New Hampshire declined 45 percent. In roughly the same period, average blood mercury concentration in loons from ten study lakes in the hotspot decreased 64 percent and yellow perch showed a 32 percent drop. These reductions were much greater than those observed elsewhere in the Northeast. Coincidence? Unlikely. Far more likely is that the data analysis provides one more reason to do all we can to keep mercury out of our waters.
Emma Downs, a student at the University of Massachusetts Amherst, wrote this article during an internship at NEIWPCC’s Lowell headquarters.
Editor’s Note: After the release of the report on the HBRF study, the Electric Power Research Institute, which is funded by a consortium of electric power producers, issued a statement strongly criticizing a number of the team’s conclusions. That statement plus HBRF’s responses and all other materials pertaining to the study are available at www.hubbardbrookfoundation.org.