The extent to which mercury in the environment poses a risk to human health has been debated for years. While the dangerous effects of high levels of methylmercury—the mercury compound of primary public health concern—are well known, questions remain regarding the health effects, if any, of low levels of methylmercury in the diet, particularly among children, infants, and the developing fetus. Recently, the United States Environmental Protection Agency (EPA) proposed regulating mercury emissions from power plants that burn coal to create electricity. While one might assume this would be an effective means of both reducing environmental mercury levels and of improving public health, the scientific evidence is much less certain.
Today, coal-fired electric power plants are the only unregulated commercial sources of mercury emissions in the United States. Opponents of new regulation claim that current environmental levels of methylmercury are not dangerous, that current technologies for limiting emissions are unreliable, and that reducing mercury emissions from US power plants will have little impact on overall environmental methylmercury levels. Proponents, however, claim that current levels of methylmercury in the environment do indeed pose a risk to the developing nervous systems of fetuses, infants, and young children. They further assert that technologies are available to substantially reduce mercury emissions and that such reductions in the US will impact environmental methylmercury levels and thereby reduce exposure and health risks.
Another topic of debate is what specific amount of methylmercury actually poses a health risk. Many experts question both the methods and the accuracy of the data used by the EPA in setting the current guidelines for methylmercury exposure. As a result, some view the EPA limit as too high—that is, underprotective—while others feel it is too low—that is, overprotective. If the EPA guidelines are more stringent than necessary—which often happens, given the safety margins built into such guidelines—then risk at current levels is highly unlikely. In that case, further regulation may be a misuse of the limited resources available for improving public health.
This booklet, based on a more technical report, examines the scientific evidence underlying claims of those for and against the regulation of mercury emissions, with the aim of determining the impact, if any, such regulation will have on public health. Specifically, it focuses on the health effects associated with methylmercury and examines the question of whether limiting mercury emissions from coal-burning plants in the US would reduce environmental methylmercury levels, and therefore, human exposure.
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