The U.S. Environmental Protection Agency on Jan. 31 moved to restore the legal underpinning for an Obama-era rule targeting harmful mercury emissions from coal- and oil-fired power plants.

The EPA's proposed rule would rescind a final regulation issued in April 2020 by the Trump administration that was opposed by the nation's largest electric utility trade group as well as environmental groups and public health advocates focused on air pollution.

Finalized in 2011, the Mercury and Air Toxics Standards, or MATS, required coal- and oil-fired electric generators to install pollution controls designed to curb mercury emissions. Coal-fired generators are one of the nation's largest sources of airborne mercury, a powerful neurotoxin that can make its way through the food chain and interfere with the development of children in the womb.

When the rule was issued, the EPA estimated it would produce between $37 billion and $90 billion in annual public health benefits compared to $9.6 billion in yearly compliance costs. However, virtually all of the public health benefits in the agency's regulatory impact analysis flowed from related reductions in fine particulate matter, with just $4 million to $6 million in direct benefits related to reduced mercury exposure.

The Trump EPA seized on that discrepancy despite lower-than-expected compliance costs and evidence from research institutions such as Harvard University that the health benefits of mercury reductions are far greater than originally projected. Harvard researchers specifically found that the annual health benefits of reductions in mercury emissions are actually about $4.8 billion instead of the low millions of dollars originally estimated by the EPA.

Legal challenges to the April 2020 final rule were put on hold as the Biden administration reviewed the regulation.

The EPA's Jan. 31 proposed rule would reaffirm a 2016 finding issued in response to a 5-4 U.S. Supreme Court ruling that faulted the agency for failing to consider compliance costs early enough in its rulemaking process.

The proposal asserted that the Trump administration's approach "discounts the vast array of adverse health and environmental impacts associated with [mercury] emissions from coal- and oil-fired [electric generating units] that have been enumerated by the EPA and discounts the social value of avoiding those impacts through regulation, simply because the agency cannot assign a dollar value to those impacts."

The Edison Electric Institute praised the EPA's proposed reversal, noting that its member companies have already invested more than $18 billion to comply with the MATS rule.

"Restoring the appropriate and necessary finding enables electric companies to remain focused on getting the energy we provide as clean as we can as fast as we can, while maintaining the reliability and affordability that our customers value," EEI President Tom Kuhn said in a statement.

Environmental groups were also quick to praise the EPA's proposal and noted the White House's Office of Management and Budget has long accounted for co-benefits.

"By considering both direct and indirect benefits in this decision, EPA revives analytic best practices cast aside by the Trump administration," Richard Revesz, director of the New York University School of Law's Institute for Policy Integrity, said in a statement. "The newly restored approach is endorsed by the Office of Management and Budget's longstanding guidance and by all respectable economists and, prior to the Trump administration, had been the norm in both Republican and Democratic administrations for decades."

Comments on the EPA's proposal are due 60 days after its publication in the Federal Register.