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Why be concerned about mercury pollution? In 1998, the EPA identified coal-fired power plants as the largest remaining source of airborne mercury emissions in the US. Additionally, the EPA identified mercury as the hazardous air pollutant of “greatest potential concern” associated with coal-fired power plants.
Mercury released into the air is carried by rain and snow back to the earth, where it falls onto surface waters, such as lakes. Once in lakes, mercury can be changed by bacteria to methylmercury (a bioaccumulative form). Top predators at the end of a long food chain, such as lake trout, large salmon and fish eating gulls and humans, may accumulate high concentrations of methylmercury even though its concentration may be very low in the open water.
Exposure to methylmercury can result in long-lasting health effects, especially on children and fetal development during pregnancy. Mercury poisoning has been linked to nervous system, kidney and liver damage and impaired childhood development. Long-term eating of mercury-contaminated fish has been associated with deafness, blindness, and death.
The United States has taken some important steps to reduce the environmental load of mercury in the Great Lakes region. For example, the Great Lakes Initiative has set tighter standards for mercury pollution from dischargers in the Great Lakes. These tighter standards are now beginning to be incorporated into the permits for industrial dischargers.
The EPA has proposed new rules to regulate the release of mercury into the air. When adopted, these rules will replace the Clean Air Mercury Rules, issued by EPA in 2005, which required reductions in emissions and created a “cap and trade” program. The 2005 rules were challenged in court and found to conflict with the standards of the Clean Air Act. In May 2011, the Alliance urged EPA to adopt strong new rules to reduce hazardous air pollutants like mercury from power plants. We expect these new rules will be adopted before the end of 2011.
Until the new rules are adopted, the release of mercury by coal fired power plants continues to be governed by the requirement that all coal plants comply with the “Maximum Achievable Control Technology” (MACT). MACT is a case-by-case determination made by reviewing “best controlled similar source” and any evidence showing that an even lower standard is achievable in practice.