Emission controls required on out-of-state power plants have yielded big reductions in mercury pollution in Western Maryland's air, a study has found. So far, however, the state's fish remain as contaminated with the toxic chemical as ever, researchers say.
Long-term monitoring at a reservoir in Garrett County saw declines of 43 percent to 75 percent in airborne mercury levels there from 2009 through last year, according to the study. Those declines tracked closely with emission reductions measured at coal-burning power plants not far away in Ohio, Pennsylvania and West Virginia.
The findings, published online recently in the journal Environmental Science & Technology, provide "compelling evidence" that regulating mercury emissions from U.S. power plants can produce significant environmental benefits downwind, conclude the authors, Mark Castro of the University of Maryland Center for Environmental Science and John Sherwell of the state Department of Natural Resources.
"It does matter, particularly regionally and locally," said Castro, a biogeochemist with UM's Appalachian laboratory in Frostburg.
Most of the mercury fouling the state's air and contaminating its fish comes from out of state, he noted.
The study comes amid a prolonged legal struggle between the Environmental Protection Agency and the electric power industry over the EPA's attempts to curb mercury emissions from coal- and oil-burning plants. Mercury is a powerful neurotoxin that can damage children's developing nervous systems, impairing their ability to learn.
The Supreme Court ruled in June that the EPA had not properly considered the costs of requiring mercury controls on power plants and ordered a lower court to take another look at the federal regulation. Late last month, the EPA announced that after further review of the costs, it still believed reductions were warranted.
The EPA's rule would protect Americans from "a host of avoidable illnesses and premature deaths" by curtailing emissions of mercury and other toxic air pollutants, according to spokeswoman Enesta Jones. Every dollar spent on emission controls would be offset by $9 in health benefits, the agency said.
The study took place before the EPA's mercury rule kicked in, so it didn't actually measure any effects from it. The reductions it tallied stemmed from controls put on power plants earlier to reduce other air pollutants, which also captured some of the mercury emissions, and from some coal plants' switching to cleaner-burning natural gas.
Castro said their findings are relevant to the dispute over the regulation because some computer models have concluded that so much of the mercury in the atmosphere is produced in other countries that emission controls on U.S. plants would yield no measurable benefits in this nation.
George S. "Tad" Aburn, chief air regulator for the Maryland Department of the Environment, said out-of-state power plants are a significant source of the mercury contaminating the state's waters and fish. The state already required a 90 percent reduction in mercury emissions from its own coal-burning power plants under the 2004 Healthy Air Act, noted Jay Apperson, an MDE spokesman.
Jeff Holmstead, a former EPA regulator who now represents industry, said the study would have no effect on the EPA's court case, as the deadline has passed for filing any new documents in it. He said it also remains an open question whether the declines in airborne mercury detected by the Maryland researchers would translate into reductions in contamination in fish. People's exposure to mercury comes primarily through eating fish, he said.
Airborne mercury tends to wind up in the water, where it settles in sediments, on which fish feed. Mercury levels detected in freshwater fish have prompted the state to recommend people limit their consumption of several species from lakes, reservoirs, rivers and streams.
Sherwell, the study's co-author, who is an atmospheric scientist in the state's power plant review section, said fish tissue from those sites is sampled annually. "We're not seeing any trends," he said.
But Castro said the effect may be muted because so much mercury is already in the environment.
"It's built up in the ecosystem. It's going to take a while," he said.