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Air Quality Issues of Electricity Production:
Mercury and Other Toxic Air Emissions



What are air toxics?

Toxic air pollutants -- also referred to as "air toxics" or "hazardous air pollutants" -- are substances released into the air that can cause cancer or other serious health effects. They may also damage ecosystems. These pollutants can come from natural sources, as is the case with radon gas. However, they are predominately generated by factory smokestacks, electric power plants and motor vehicles. The federal Clean Air Act lists nearly 200 hazardous air pollutants as targets for clean-up that include heavy metals like mercury and chromium, organic chemicals like benzene, and dioxins.

Mercury has been the focus of regulatory activity because of its documented carcinogenic effect, as well as its persistent prevalence in the environment. Since mercury is volatile and readily mobilized, and often travels great distances before being deposited, regulatory concern about the environmental impacts of mercury appear to be quite justified.


What are the consequences of air toxics?

Although much remains to be learned about the human health effects of mercury and other air toxics, scientists have linked these pollutants to neurological, cardiovascular, and respiratory disease. Effects on the liver, kidney and immune system have also been documented. Fetal and child development may too be harmed by mercury and air toxics. Some health effects are immediate. Such was the case in Bhopal, India in 1984 when more than 2,000 people were killed by the accidental release of methyl isocyanate. Other health impacts associated with air toxics may not manifest themselves for several months or years after exposure, as is the case with leukemia, a form of cancer typically caused by chronic exposure to benzene in the workplace.

Some air toxics pose a special health risk to sensitive human populations -- such as young children or senior citizens. The EPA reports that roughly a third of the 200 air toxics can harm the development of a fetus, causing birth defects or miscarriages, and can prevent young children from growing into healthy adults.

Mercury poisoning is illustrative of the exposure pathways and health risks of all air toxics. Atmospheric concentrations of mercury at toxic levels are rare. Nonetheless, mercury washes out in rainfall and bioaccumulates in the tissue of animal and fish in an even more toxic form. Bioaccumulation means that concentrations of mercury in predators at the top of the food chain can be thousands -- and even millions -- of times greater than the concentrations found in the water they drink.

Human exposure to mercury typically occurs when contaminated fish are eaten as food. Over 40 states have issued health advisory warning against the consumption of certain species of fish because of this fear. In the words of the U.S. Environmental Protection Agency, "Neurotoxocity is the health effect of greatest concern with mercury exposure....Children born of women exposed to relatively high levels of methylmercury during pregnancy have exhibited a variety of developmental neurological abnormalities, including delayed onset of walking and talking, cerebral palsy, and reduced neurological test scores." (U.S. EPA, Mercury White Paper)

Reproductive effects in wildlife are also of major concern. At concentrations well below those considered to be lethal, mercury has been found to impair the reproductive function of predatory birds and mammals that subsist on fish, resulting in lower egg hatching rates, lower birth weights and delayed motor development. Beavers, bears, eagles, gulls and loons have all exhibited these disturbing symptoms.


How does electricity production contribute to increased levels of mercury and other air toxics?

The smokestacks of power plants spew a broad range of toxic substances into the air. Included among these chemical vapors are known carcinogens such as mercury, heavy metals (arsenic, beryllium, cadmium, nickel), dioxin, furans and PCBs. Based on a recent national inventory of hazardous air pollutants released into the air by electric power plants, EPA found that coal and oil fired generating units represent a major source of several major hazardous air pollutants. Other generating technologies - especially waste-to-energy facilities (municipal solid waste, tire burning and wood waste) also contribute to the nation's inventory of listed hazardous air pollutants. By contrast, natural gas plants and facilities relying on renewable energy sources have negligible or no toxic emissions, respectively.

Coal fueled electric power plants are the single largest source of mercury emissions. An inventory of mercury emissions conducted by EPA found that one-third of all mercury air emissions come from coal burning electric power plants. Mercury is present in the coal used as feedstock in the utility boiler. As the coal is combusted in the utility boiler, mercury is vaporized and released as a gas. Pollution controls employed by utilities to curb other pollutants are not effective in removing mercury. At present, there are no commercially viable control technologies for mercury. As a consequence, this highly toxic form of air pollution continues to go largely unabated.


How can consumer electricity choice address mercury and other air toxics?

Consumers can choose to buy their electricity from products certified as being comprised of renewable energy sources. Among the renewable resources, solar, wind and hydropower technologies emit zero air emissions. Biomass and geothermal fuels, as well as state-of-the-art natural gas facilities, may emit tiny amounts of air toxics. In contrast, coal, oil, and waste-to-energy facilities emit significant amounts of toxic air pollutants. While pollution control technologies for these sources could become commercially available, the high costs likely preclude widespread use in a competitive power market. By choosing a power product that does not emit mercury or other air toxics, consumers can send a signal to electricity suppliers to not deploy existing power plants, or build new facilities, that generate these deadly emissions.


References:

EPA, Mercury Study Report to Congress, Vol.2: An Inventory of Anthropogenic Mercury Emissions in the United States (1997).

Center for Clean Air Policy, Mercury and Utilities: Science and Technology Roundtable Proceedings (1997).

The Energy Project, Land and Water Fund of the Rockies, How the West Can Win: A Blueprint for a Clean and Affordable Energy Future (1996).

ESEERCO, New York State Environmental Externalities Cost Study Vol. 1 (1995).

U.S. Environmental Protection Agency's Mercury White Paper http://www.eoa.gov/ttn/oarpg/t3/memoranda/whtpaper.pdf

OAQPS, EPA, Study of Hazardous Air Pollutant Emissions from Electric Utility Steam Generating Units, Final Report to Congress (last modified Feb. 25, 1998) http://www.epa.gov/ttn/oarpg/t3/reports/utilexec.html

OAR, EPA, Air Toxics (last modified Mar. 3, 1999) http://www.epa.gov/oar/airtoxic.html

OAR, EPA, Mercury Study Report to Congress: White Paper (last modified Mar. 3, 1999) http://www.epa.gov/oar/merwhite.html

Pace University Center for Environmental Legal Studies, Environmental Costs of Electricity (1990).


Additional Information:
Minnesotans for an Energy Efficient Economy (ME3) / Mercury http://www.me3.org/projects/mercury/

Center for Clean Air Policy / Air Quality Program: Mercury http://www.ccap.org/

Environmental Defense "Scorecard Web Site" profile of mercury pollution http://www.scorecard.org/chemical-profiles/summary.tcl?edf_substance_id=7439%2d97%2d6

Text of this page revised April 16, 2002


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