09/27/2017 - Regulatory Rollback

Mercury and Air Toxics Standards

by Caitlin McCoy, Robin Just

The Environmental & Energy Law Program is tracking the environmental regulatory rollbacks of the Trump administration. Click here for the list of rules we are following. If you’re a reporter and would like to speak with an expert on this rule, please email us.

Why it Matters

Mercury and Air Toxics Standards (MATS) limit the amount of mercury and other toxic emissions from power plants. Mercury is a powerful neurotoxin that ends up in the water and soil, and concentrates up the food chain, especially in fish. It is particularly dangerous for pregnant women and young children. If the Environmental Protection Agency (EPA) were to reconsider or rescind the rule, power plants could stop operating with installed pollution controls.

Read legal analysis pieces on potential impacts of changes to the rule written by our Executive Director Joe Goffman:

Dec. 21, 2018 – MATS, Cost-Benefit Analysis, and the Appropriate and Necessary Finding

Dec. 17, 2018 – Preview: Mercury and Air Toxics Standards (MATS) – EPA Review and Legal Analysis of MATS Rule and MATS Review Proposal

March 14, 2019 – Rolling Back the Mercury and Air Toxics Standards: Proposed Withdrawal of “Appropriate and Necessary”

Current Status

Dec. 28, 2018 EPA releases a proposal to revise the 2016 Supplemental Finding and risk and technology review for MATS. The proposal would limit consideration of health benefits in the cost-benefit analysis performed for the regulation. The comment period for the proposed rule was open until April 17 and 495,808 comments were submitted


Dec. 2011 The Mercury and Air Toxics Standards are signed, and coal- and oil-fired power plants are required to make reductions to achieve those standards by Spring 2016. Industry challenges the rule; it is upheld by the D.C. Circuit in 2014 and goes up to the Supreme Court.

Feb. 16, 2012 EPA issues the final Mercury and Air Toxics Standards. Industry groups and several states challenge the rule. Michigan v. EPA, No. 14-46 (lead case) (D.C. Cir.).

June 29, 2015 The Supreme Court remands MATS to the D.C. Circuit to assess how EPA should proceed with additional cost-benefit analyses. The D.C. Circuit sends the MATS back to EPA to determine if the standards are “appropriate and necessary.”

April 25, 2016 EPA publishes its Supplemental Finding on the costs and benefits of MATS and finds them to be justified in light of the enormous anticipated health benefits. Within hours, opponents sue. Murray Energy v. EPA, No. 16-1127 (D.C. Cir.).

Trump Era

Jan. 31, 2017 Petitioners seek a 45-day extension in the briefing schedule.

Feb. 9, 2017 The D.C. Circuit denies the extension.

April 18, 2017 EPA asks the Court to delay oral arguments, scheduled for May 18, 2017.

April 27, 2017 The D.C. Circuit removes the argument from its calendar, suspending the case indefinitely, and directs EPA to file 90-day status reports.

July 10, 2018 The Edison Electric Institute and several other industry trade groups and unions send a letter to EPA air chief Bill Wehrum asking him to leave the MATS in place and finish the residual risk and technology review “as expeditiously as possible.” The letter also emphasizes that “…all covered plants have implemented the regulations and that pollution controls — where needed — are installed and operating.”

Aug. 24, 2018 Senators Tom Carper (D-Del.) and Lamar Alexander (R-Tenn.) send a letter to acting EPA Administrator Andrew Wheeler urging EPA to retain MATS. The senators explain, “Keeping the current rule in place will provide much-needed certainty for the electric power industry and help protect the health of all Americans.”

Oct. 1, 2018 EPA confirms it has sent a draft proposal to the White House Office of Management & Budget for review that would change the agency’s methodology for weighing economic costs and benefits used in the 2012 rule. The new proposal would eliminate consideration of co-benefits of the regulation—the benefits associated with reducing other emissions, besides mercury and other toxic pollutant emissions, that also occur under the rule.

Dec. 28, 2018 EPA releases a proposal to revise the 2016 Supplemental Finding and risk and technology review for MATS. The proposal would limit consideration of health benefits in regulation. For more information about the impacts of the issues in this proposal, read EELP Executive Director Joe Goffman’s discussion of potential changes EPA could make here.

Jan. 22, 2019 Michigan Attorney General files a motion withdrawing from litigation challenging the Obama-era MATS rule.

March 18, 2019 A bipartisan group of six senators send a letter to EPA Administrator Wheeler, urging him to withdraw the proposal to revise the “appropriate and necessary” finding and voicing their opposition to any action that could lead to undoing the Mercury and Air Toxics Standards.

March 21, 2019 Wisconsin withdraws from legal challenge to Obama-era MATS rule. 

March 26, 2019 Several industry trade groups and labor unions send a letter to EPA air chief Bill Wehrum urging EPA to maintain its 2012 regulations and “…take no action that would jeopardize these investments or the underlying rule.” The letter also suggested that “…EPA should consider the impacts such an action would have on these costs already borne by industry and how the recovery of these sunk costs could be put in jeopardy….”

April 17, 2019 The attorneys general of 21 states submit comments to EPA opposing its proposal to withdraw the appropriate and necessary finding.

For More Information

See Save EPA’s Saving the Mercury and Air Toxics Standards.