The Clinic has worked for a number of years on efforts to reduce exposure to methylmercury, a potent neurotoxicant. In particular, the Clinic has filed amicus briefs and comment letters at every stage of the ongoing battle over the Environmental Protection Agency’s Mercury and Air Toxics Standards (MATS) for power plants, going back to the initial D.C. Circuit litigation in 2013. Most recently, the Clinic submitted comments on behalf of a group of leading scientists on EPA’s proposed Integrated Risk Information System (IRIS) Assessment Plan for methylmercury.

The Dangers of Mercury Emissions

Methylmercury is a highly toxic, bioaccumulative, and persistent pollutant. Over the last century and a half, anthropogenic mercury emissions have dramatically increased mercury levels in the environment. Coal-fired power plants are the largest source of mercury emissions in the United States, accounting for 42% of emissions in 2014.

Source: Harvard Magazine


Once mercury is deposited in the environment, it can be transformed by microbial processes into methylmercury and in this form is taken up by organisms at the base of the food chain. Methylmercury biomagnifies, that is, increases with each level of the food chain, and attains its highest concentrations in predatory species at the top of the food chain. Human exposure to methylmercury occurs primarily through consuming fish in which methylmercury has bioaccumulated.

Methylmercury is a highly toxic substance that targets the nervous system. Infants and fetuses are at the highest risk, both because the developing central nervous system is particularly sensitive to methylmercury and because methylmercury can cross the placental and blood-brain barriers. In addition, methylmercury compromises cardiovascular health; high concentrations of methylmercury in blood and tissue samples have been strongly associated with acute coronary events, coronary heart disease, and cardiovascular disease. It has also been associated with a variety of other adverse health impacts and threatens many species of aquatic and terrestrial birds and mammals.

The MATS Rule and the Clinic’s Involvement

EPA regulates emissions of toxic air pollutants such as mercury under section 112 of the Clean Air Act. When Congress amended the Clean Air Act in 1990, it directed EPA to set emissions standards for all major sources of 189 toxic air pollutants under a strict timeline. The one exception was emissions from coal-fired power plants. Congress in those same 1990 amendments had created the acid rain cap-and-trade program—which applied only to coal-fired power plants—and it was thought that the controls that power plants installed to reduce sulfur dioxide emissions might also reduce emissions of mercury and other air toxics. Therefore, Congress instructed EPA to determine whether it was “appropriate and necessary” to regulate power plant emissions under section 112 after taking into account the effect of the acid rain program.

In the end, power plants largely complied with the acid rain program by switching to low-sulfur coal, and coal-fired power plants remained the leading source of mercury emissions in the United States. EPA therefore determined in 2000 that it was appropriate and necessary to regulate toxic air pollutant emissions from power plants. It confirmed this finding in 2012 and for the first time established mercury emissions limits for coal-fired power plants in the MATS Rule.

Industry groups and a number of states challenged the MATS Rule in the D.C. Circuit. The Clinic submitted an amicus brief in support of the rule on behalf of a group of law professors including Professors Freeman and Lazarus, arguing that EPA’s regulatory approach was justified by the history and text of the Clean Air Act. The D.C. Circuit upheld the rule.

The case was then appealed to the U.S. Supreme Court, where the Clinic again submitted an amicus brief, this time on behalf of the Union of Concerned Scientists. In its brief, the Clinic argued that Congress, in directing EPA to issue regulations if “appropriate and necessary,” intended that the agency make a scientific decision based on the public health impacts of the industry’s emissions.

The Supreme Court ruled that EPA needed to consider costs when making the “appropriate and necessary” finding and remanded the decision to the agency. On remand, EPA undertook an evaluation of costs and reaffirmed its prior finding. The Clinic submitted a comment letter during the remand and an amicus brief in the subsequent D.C. Circuit litigation on behalf a group of leading scientists, including Elsie Sunderland from the Harvard John A. Paulson School of Engineering and Applied Sciences, Philippe Grandjean, from the Harvard T.H. Chan School of Public Health, and Charles T. Driscoll. Jr. from Syracuse University.

The Trump Administration’s Proposed Rollback

The Trump Administration has now proposed to reverse its finding that it is appropriate and necessary to regulate power plant mercury emissions. In the spring of 2019, the Clinic submitted comments opposing that proposal. Our comments explain that:

  • EPA’s proposal is based on an eight-year-old analysis which even at that time was incomplete and which underestimated the benefits of regulating power plant mercury emissions.
  • The scientific literature includes significant new evidence of the benefits of regulating power plant mercury emissions, including estimates of those benefits that are orders of magnitude larger than EPA’s.
  • It is now clear that reductions in mercury emissions from power plants result in localized and regional reductions in atmospheric mercury deposition, which amplifies the benefits of decreasing domestic emissions.
  • The entire industry has by now come into compliance with the mercury and air toxics standards. It is therefore no longer necessary to rely on predictions of the compliance costs. Multiple analyses have estimated that the actual costs of compliance are less than a billion dollars per year compared to the $9.6 billion per year EPA predicted in 2011.
  • Regardless of whether EPA can reverse the appropriate and necessary finding, it does not have the authority to delist power plants or repeal their emissions standards without going through the section 112(c)(9) delisting process.

Examples of the Clinic’s Mercury-Related Work Product: