November 01, 2017

Why EPA’s Mercury and Air Toxics Standards matter—history and health

James L. Simpson

Coal-fired power plants are the largest source of mercury emissions in the United States, and the regulation of their emissions has a long history; but the health impacts of the Mercury and Air Toxics Standards (MATS) rule should be substantial.

Regulatory history

Until 2012 there were no federal standards to control emissions of toxic air pollutants such as mercury and arsenic from power plants, despite the availability of control technology and the U.S. Environmental Protection Agency’s (EPA’s) well-established National Emission Standards for Hazardous Air Pollutants (NESHAP) under the Clean Air Act. The 1990 Clean Air Act Amendments required EPA to issue standards to reduce emissions of hazardous air pollutants (HAPs) from many sources and to study whether to do so from power plants. See 42 U.S.C. § 7412(n)(1)(A). Congress wanted EPA to implement other provisions of the Clean Air Act first and then decide whether it was still necessary to regulate power plants directly.

EPA completed the required study in 1998. In 2000, EPA determined it was “appropriate and necessary” to regulate the emission of nearly 200 air toxics from power plants and added power plants to the Clean Air Act section 112(c) source category list. See 65 Fed. Reg. 79,825, 27 (Dec. 20, 2000). EPA reversed this finding in 2005, but in 2008 the D.C. Circuit vacated EPA’s decision to remove power plants from the CAA section 112(c) source category list. See New Jersey v. EPA, 517 F.3d 574 (D.C. Cir. 2008). Ultimately, pursuant to a consent decree after additional litigation, EPA issued proposed standards for the control of HAPS from power plants on March 15, 2011.

Background of MATS

EPA issued the final MATS rule for coal-and oil-fired power plants on February 16, 2012. See 77 Fed. Reg. 9304 (Feb. 16, 2012). According to EPA, reducing emissions of mercury and other HAPs from the electric power industry will also have significant co-benefits of reductions in SO2 and PM2.5, largely in reduced human mortality. EPA estimated high compliance costs of almost $10 billion, but monetized benefits of between $33 billion and $90 billion. EPA estimated the MATS rule would reduce power plant mercury emissions by 90 percent and, also, dramatically reduce emissions of other toxics like arsenic, nickel, dioxins, and acid gases.

Health impacts of mercury and air toxics

Mercury emissions make their way to waterbodies, where bacteria convert the mercury into the more toxic methylmercury (MeHg) that can bioaccumluate, especially in fish and shellfish. In turn, eating contaminated fish (and animals that eat the fish) is the largest source of human and wildlife exposure to organic mercury. Pregnant women are especially at risk because MeHg can cause neurological disorders in developing fetuses. In its appropriate and necessary finding, EPA found a “plausible link” between power plants’ mercury emissions and MeHg in fish. 65 Fed Reg. 79,825, 27 (Dec. 20, 2000). EPA also found “that about 7 percent of child-bearing age women are exposed to MeHg at levels capable of causing adverse effects to the fetus, and about 1 percent were exposed to 3 to 4 times that level.” 76 Fed. Reg. 24,978. By 2011, all 50 states had issued fish advisories for mercury, totaling 16.4 million lake acres and 1.1 million river miles.

In addition to mercury, coal-fired power plants emit carcinogenic HAPs such as arsenic, nickel, cadmium, and chromium. Other toxic pollutants released include lead and the acid gases hydrogen chloride (HCl), and hydrogen fluoride (HF). According to EPA, these pollutants can cause lung irritations, central nervous system effects, kidney damage, and other acute disorders. See 76 Fed. Reg. 24,978.

What the MATS rule does

Generally, the MATS rule applies to power plants larger than 25 megawatts that burn coal or oil to generate electricity for sale and distribution through the national electric grid. EPA estimates the MATS rule impacts approximately 600 power plants, which include 1,100 existing coal-fired units and 300 oil-fired units. The rule provides numerical emission limits for mercury, particulate matter (PM), and HCl for existing and new coal-fired power plants, and numerical emission limits for PM, HCl, and HF for existing and new oil-fired power plants, using a variety of technologies to achieve these limits. The MATS rule also establishes work practice standards, instead of numerical limits, to limit emissions of organic air toxics from existing and new coal- and oil-fired power plants.

The MATS rulemaking attracted a lot of public attention; EPA received close to 1 million public comments on the proposed rule, substantially more than any prior rulemaking.

Supreme Court decision on costs

In 2015 the Supreme Court held that EPA acted unreasonably when it deemed cost irrelevant in its MATS “appropriate and necessary” finding. See Michigan v. EPA, 135 S. Ct. 2699, 2712 (2015). In response to this ruling, EPA interpreted this decision narrowly and did not alter the MATS rule issued previously, but conducted a supplemental review and found that a consideration of costs does not change EPA’s earlier appropriate and necessary finding. In this supplemental finding, EPA concluded that $9.6 billion annual costs of compliance should save at least $37 billion in co-benefits. See 81 Fed. Reg. 24,247 (Apr. 25, 2016).

What lies ahead?

There is good news to report. According to EPA’s Toxics Release Inventory (TRI), U.S. air releases of toxic chemicals decreased by 56 percent (nearly 400,000 tons) from 2005 to 2015, including significant decreases in emissions of hydrochloric acid, sulfuric acid, toluene, and methanol. EPA attributes the decrease to electric utilities shifting from coal to other fuel sources, the installation of control technologies at coal-fired power plants, and the implementation of environmental regulations like the Acid Rain Program. In particular, mercury from coal- and oil-fired power plants declined 69 percent during this period. However, EPA reported that electric utilities still accounted for 48 percent of the mercury air emissions reported to TRI, demonstrating the continued need for MATS.

Apart from these emissions reductions, opponents of the MATS rule have not stopped litigating. Indeed, the Trump administration’s professed desire to stop the putative “war on coal” raises the question of how hard the current administration will defend the MATS rule. On April 27, 2017, the D.C. Circuit Court of Appeals granted EPA’s motion to delay oral arguments in a case challenging EPA’s supplemental appropriate and necessary finding on costs. EPA stated in its motion that political appointees were reviewing the supplemental finding to determine whether EPA should reconsider the MATS rule.

James L. Simpson

James Simpson is vice chair of Electronic Communications for the SEER Air Quality Committee and a former assistant regional counsel at U.S. EPA, Region 2.