Grappling with Mercury

On the last day of June, the Environmental Protection Agency formally wrapped up a lengthy public comment period on a proposed rule to limit mercury emissions from coal-fired power plants, the nation's largest mercury emitter.

EPA's proposed regulation has been fraught with controversy. It has generated more than a half million comments from utilities, citizens, public health professionals, scientists, environmental groups, state regulators, members of Congress, and others. The regulation has been stalled for a decade, and EPA is under court order to issue a final rule next year.

Mercury is a big concern. It is a pervasive global pollutant. Mercury vapor may circulate in Earth's atmosphere before being deposited to land and sea. Or, new research shows it can also be found near the very source where it was first emitted to air.

Mercury is neurologically toxic, particularly for children. EPA estimates that some 630,000 U.S. children are born each year with learning deficits caused by mercury exposure.

Human exposure is mostly through fish consumption, and the primary health concern is that pregnant women will expose their developing babies to mercury by eating contaminated fish. Mercury, particularly methylmercury, bioaccumulates and concentrates in fish. More than 40 states have warnings against eating lake fish because they are contaminated with mercury, and mercury is becoming a worldwide problem with tuna, swordfish, and other large species of sea-going fish showing high levels.

Most global mercury emissions come from burning coal. Even though EPA's proposals pertain only to the U.S., the actions that the federal government and U.S. coal-burning utilities take to address mercury emissions are likely to set a technological path for poorer nations.

Coal is a cheap and abundant source of energy not just in the U.S., but also in China and India, where people lack--but certainly want--electricity on a scale like that of the U.S.

U.S. Energy Information Administration officials estimate that some 5.3 billion metric tons of coal is burned annually worldwide, and that number is expected to grow by more than 2 billion metric tons by 2025, mostly because of increased electricity generation in China.

In the U.S., coal-burning electric power plants are the largest source of mercury air emissions (48 metric tons per year). They produce about one-third of all U.S. anthropogenic mercury air emissions.

Many of these plants are 40 or more years old and have little air pollution abatement equipment for mercury or other pollutants. They generate 53% of U.S. electrical energy, however, and can take credit and blame for providing the nation's cheapest electricity and its dirtiest air emissions.

In late December 2003, EPA offered alternative proposals to regulate mercury emissions from coal-fired electric utilities (C&EN, Dec. 22, 2003, page 12).

One proposal would require utilities to install "maximum achievable control technologies" by 2007 that would cut mercury emissions by 29%: from 48 to 34 metric tons annually. To make this reduction, utilities would install technologies required under regulations for other pollutants--nitrogen oxides and sulfur dioxide--and capture mercury as a cobenefit.

Another approach, favored by EPA and utilities, would create a "cap and trade" program in which utilities would be able to buy and sell credits for mercury removal, similar to the system used for sulfur dioxide under the Clean Air Act's acid rain program. The mercury trading program would be phased in by 2018 or later and, once fully implemented, would cut mercury emissions by 69% to 15 metric tons annually.

Under federal environmental laws, however, mercury is considered a toxic pollutant, and, as such, EPA must change the Clean Air Act, which forbids trading toxic pollutants. That change is also part of the current proposal.

The issue of mercury trading concerns environmental groups, public health officials, some state regulators, and members of Congress.

These critics argue that the cap can be met too easily. Economists with the think-tank Resources for the Future warn that the Bush Administration's mercury cap will produce little trading and no technological innovations and, in the end, will discredit the idea of emissions trading.

Critics also worry that the proposals do not address mercury "hot spots," where high mercury concentrations near emissions sources have been found. Hot spot fears were elevated by a Florida Department of Environmental Protection study last year that found that installation of mercury emissions controls at a Florida waste incinerator led to a 60 to 70% reduction in mercury concentrations in wildlife near the incinerator.

TRADING WOULD ALLOW utilities to choose where they make reductions, making no reductions for some plants and instead buying credits. Therefore, people living or fishing near a mercury hot spot source could remain subject to mercury contamination, despite the regulation.

Opponents instead want EPA to propose a different plan, one that was reached in October 2002 after long negotiations between industry, state regulators, environmental activists, and citizens. The Administration discarded this plan last year and substituted its proposal.

State environmental officials were involved in those negotiations, says the Environmental Council of the States (ECOS), an organization of state regulators. ECOS chides EPA for ignoring stakeholders' views in its proposed rule and notes that the agreement would have reduced mercury air emissions by 40 to 96% by 2007 using available technology.

The potential of current technologies to capture mercury and whether EPA will require them are questions with a significant impact, not just in the U.S. but in developing nations that have large coal reserves and growing electricity demands.

Total annual mercury air emissions in the world are in the 6,000- to 6,600-metric-ton range, with roughly one-third coming from natural sources and two-thirds from direct and recirculating anthropogenic sources, says Alexis Cain, an EPA environmental scientist. He warns, however, that these numbers are highly uncertain.

About half the anthropogenic sources are in Asia; China is at the top, followed by India. Europe and the U.S. combined have significant emissions, but they are declining, Cain says.

The largest global emissions source is coal combustion, followed by low-technology gold and silver mining, smelting, and waste combustion.

U.S. anthropogenic emissions (160 metric tons per year) are relatively small--about 3% of the global total of all emissions. About 85% is from combustion sources, and the largest of those are coal-fired electric utilities.

EPA estimates that the U.S. power sector accounts for only about 1% of total global mercury emissions.

The small contribution is stressed by the Electric Power Research Institute (EPRI), an electric-utility-funded R&D facility in California. In comments on the EPA proposal, EPRI downplays the importance of utility emissions, saying that 70% of U.S. utility mercury emissions are deposited outside U.S. borders and that 75% of mercury deposited in the U.S. comes from sources outside the U.S.

The institute says utility-created mercury hot spots are nearly nonexistent, making up only 0.4% of U.S. land.

EPRI has also questioned the efficacy of pollution-control technologies to capture mercury. George R. Offen, EPRI senior technical leader, told Congress last November that about 40% of mercury could be captured using current technologies for NO_x and SO₂ emissions controls. He also acknowledged that with some eastern U.S. bituminous coal, washing to remove mercury could cut another 25 to 35% before coal gets to the power plant.

But he warned that mercury removal rates can vary widely--from 10 to 90%--depending on the type of coal burned and the pollution-control technology used.

MERCURY IN FLUE GAS is a mix of elemental, water-insoluble mercury and oxidized, water-soluble mercury, Offen says, and the ratio depends mostly on the coal type. The success of control technologies varies with the coal species, he argues.

However, environmental groups; regulators; and the Institute of Clean Air Companies (ICAC), consisting of some 80 makers of pollution-control equipment, disagree.

ICAC points to studies showing that fabric filters and other technologies that capture SO₂ and NO_x emissions will also capture 72 to 83% of mercury in either bituminous or subbituminous coals, the most common coals for electricity generation. They note that the addition of activated carbon to flue gases to help collect mercury can result in 90% reduction.

ICAC's opinion is that EPA's proposals will actually stall pollution-control technology development and innovation. The proposals will also block installment of controls to cut the more conventional pollutants: NO_x, SO₂, and particulates.

EPA intends to sort through these views and issue a final regulation by March 15, 2005. However, in the end, the final rule may depend more on the November elections.

Congress is split on how to address mercury. Last month, 180 House members urged EPA to reconsider the proposal, and in April, nearly half the Senate urged the same. A change of president and head of EPA would certainly halt consideration of the current regulation. The Natural Resources Defense Council, which sued to get EPA to act in the first place, has signaled that it will accept a delay if the regulation is reproposed along lines it finds acceptable.

Utilities and EPA have made clear their intention to drive ahead.