Science News - March 4, 2004

Mercury trading scheme raises concerns

In proposing pollutant trading as means to reduce mercury from coal-fired power plants, the U.S. EPA is contemplating an action that its own water agency program expressly discourages—trading in persistent bioaccumulative toxics. But this is only one of the reasons that the agency has been inundated with criticism since January, when the proposal was issued. Scientists are also questioning the agency’s stated aim to cut mercury as quickly as possible with the trading plan, because some analyses show that the trading plan would be less effective than the plan it supplants.

Opponents of the proposal voice concerns about the plan’s long time frames for significant cuts in airborne mercury levels, which in turn could make water quality goals difficult to achieve and leave toxic hotspots. Many experts argue that existing and emerging technologies can bring about steeper mercury reductions more quickly. The speed with which mercury reductions can be achieved takes on added significance in light of the growing body of scientific research indicating that mercury reductions today can translate into observable ecosystem improvements within a decade rather than over generations, as previously thought.

EPA’s own data show that numerous waters nationwide are impaired because of mercury contamination, and 44 states currently issue fish consumption advisories related to mercury. Atmospheric deposition from global and national sources is thought to be behind much of this contamination, with coal-burning power plants contributing the largest portion. In the United States, EPA estimates that these utilities emit 48 tons of mercury annually.

The controversy centers on EPA’s Utility Mercury Reductions Rule, which lays out two approaches. One would require utilities to install currently available pollution controls known as maximum achievable control technologies (MACTs). EPA estimates that this approach, if implemented, would reduce mercury emissions 29% by 2008. The alternative approach, which is EPA’s stated preferred choice, would set a mandatory, declining cap on total mercury emissions and allow utilities to buy emission credits from other utilities in order to comply with clean air rules.

EPA estimates that the market-based trading program would reduce mercury emissions 70% by 2018. But critics say this timeframe is too long and that existing and emerging reduction technologies could achieve a 90% reduction more quickly under a MACT approach.

EPA’s trading scheme, as well as the agency’s 2003 water quality trading policy (Environ. Sci. Technol. 2003, 37, 216A–223A), is based on the acid rain trading program of the 1990 Clean Air Act amendments. The acid rain programs “resulted in more reductions than required, sooner than required with a very high rate of compliance and no litigation to hold up the progress,” according to EPA officials. But the acid rain program targets sulfur dioxide (SO₂) emissions, and the water program is geared to reducing nutrient and sediment loadings to waterways, not hazardous pollutants like mercury.

“If something were to go wrong [with SO₂ or water trading], and you got a temporary overloading of nutrients, it’s something that can be cleaned up and will eventually go away,” says Suzie Greenhalgh, a senior associate at the World Resources Institute. “A bioaccumulative toxin is a whole different story.”

Charles Driscoll, a professor of civil and environmental engineering at Syracuse University, has compiled a decade’s worth of mercury research. He points out that mercury has a shorter residence time in the atmosphere than SO₂, particularly the reactive gaseous and particulate forms, which fall out fairly close to the source. Once in area waterways, this deposited mercury can transform into methylmercury, which bioaccumulates in fish and animal tissues.

A recent study of common loons in southeastern New Hampshire by the Biodiversity Research Institute (BRI) indicates that these mercury deposition patterns can result in biological hotspots. “We found extremely high mercury levels in the biota in that area,” which also happens to be populated by a number of municipal incinerators, says David Evers, BRI’s executive director. At the same time, he attributes the rapid decline in mercury levels observed in loons over the past couple of years to policy and regulatory changes made by the state to curb emissions from municipal incinerators.

Environmental groups, too, worry about hotspots. “Certain areas may not be cleaned up at all, or cleaned up very little, because some utilities would be able to buy emission credits as opposed to making actual cleanups,” says Frank O’Donnell, executive director of the Clean Air Trust.

Representatives of electric power industry groups, for their part, voice cautious support of EPA’s cap-and-trade approach for bringing mercury emissions down. However, many state environmental officials had been banking on a MACT approach. In fact, both of EPA’s proposed approaches fall short of a goal adopted in August 2003 by state air, water, and solid waste management directors that advocated the “greatest reductions possible within the shortest timeframe,” says Marcia Willhite, chief of the Illinois EPA’s Bureau of Water.

Scientific findings also make the case for quick action. Preliminary results from mercury pathway experiments in northeast Ontario in Canada suggest that mercury recently deposited from the atmosphere is more bioavailable than existing mercury. In the study, known as the Mercury Experiment To Assess Atmospheric Loading in Canada and the United States, or METAALICUS, researchers are trying to determine what happens to fish mercury concentrations when changes occur in the amount of atmospheric mercury deposition (Environ. Sci. Technol. 2001, 35, 229A–230A).

By dosing a watershed with stable mercury isotopes, “We’re finding that the mercury we add to the lake surface is much more prone to become methylated in sediments than relic mercury,” says David Krabbenhoft, a research scientist with the U.S. Geological Survey who is involved with the study. “This is important because if the pools of mercury that exist in upland and wetland soils were very active, we could be in for a long delay in terms of how long a recovery might take. If it’s only the mercury that falls directly on the lake, we’d expect the system to respond much more quickly” to any curbs on mercury emissions.

Research in the Florida Everglades also suggests that reducing air emissions could rapidly decrease mercury concentrations in fish and wading birds—much more quickly than researchers thought ecosystems would respond to reduced loading—according to Tom Atkeson, a scientist with the Florida Department of Environmental Protection.

“We started out thinking of this as an aquatic problem, but we learned that it was really driven by atmospheric processes,” he says. Atmospheric deposition of mercury dropped significantly in the late 1980s because of regulations on emissions from municipal solid waste incinerators and voluntary actions to remove mercury from household batteries. Mercury levels in fish and wildlife from the Everglades continued to rise, peaking in the mid 1990s. “Today, mercury concentrations are down by roughly 75% from that peak” as a result of the emission control policies, Atkeson notes.

EPA officials, for their part, recognize that their mercury plan has its critics. “We’re eager to hear them,” says spokesperson John Millett. He admits that water hotspots could form in some areas as a result of a cap-and-trade program, but he maintains that monitoring should keep any problems in check.

“It’s envisioned that we’re going to see some major overall improvements with the trading approach, but we’re not sure where. It may also be that some areas won’t improve, and again, we’re not sure where,” Millett notes. But right now, “We want to cut mercury as much as possible, and then with the monitoring information developed through the cap-and-trade program, we’ll be able to refine the approaches and reduce mercury in any problem areas that arise.”

For more information on EPA’s mercury proposals, go to www.epa.gov/mercury. —KRIS CHRISTEN