EPA May Limit Use of New Science in Air Pollution Rules

The Environmental Protection Agency (EPA) is currently questioning its legal authority to revise hazardous air pollution rules more than once, even when new scientific data reveals unacceptable health risks. This reconsideration, found in government records, centers on the interpretation of the Clean Air Act. The specific focus involves regulations for ethylene oxide, a gas used in sterilizing medical equipment that was found to be 30 times more carcinogenic than previously thought in a 2016 study.

In 2024, the EPA approved stricter rules to limit emissions of this chemical, which causes lymphoma and breast cancer. However, chemical companies and their trade organizations argue that the agency does not have the authority to reevaluate these rules if they have already been revised once. If the EPA agrees with this interpretation, it could significantly curb the agency's ability to update regulations for nearly 200 pollutants. This would prevent the agency from reacting to future discoveries about chemical toxicity or underestimated pollution levels from industrial facilities.

For years, ethylene oxide was considered an unremarkable pollutant, seeping from relatively few industrial facilities. This perception changed drastically in 2016 when the EPA completed a study revealing the chemical is 30 times more carcinogenic than previously believed. Following this discovery, the agency spent years updating regulations to protect the millions of people most exposed to the compound. In 2024, the EPA finalized these stricter rules, requiring commercial sterilizers for medical equipment and large chemical plants to slash emissions of the gas.

This process followed a standard agency practice: revising rules based on new scientific knowledge. However, this ability is now under threat. The EPA's current reconsideration focuses on whether the agency had the legal authority to update those rules in the first place. The agency's Office of Inspector General had previously cited the new toxicity conclusions regarding ethylene oxide, estimating that nearly half a million Americans were exposed to unacceptable cancer risks from industrial emissions. The office advised the agency to conduct new residual risk reviews when new data indicates a pollutant is more toxic than previously determined.

The debate over the EPA's authority has drawn sharp lines between industry representatives and environmental advocates. Chemical companies and their trade organizations, such as the American Chemistry Council, contend that the EPA overestimated the risks posed by ethylene oxide. They argue that the agency did not have the authority to conduct new risk reviews after the initial mandatory reviews were completed in the early 2000s. In a 2023 letter, the American Chemistry Council stated, "The agency has erred in conducting a new risk review."

Conversely, environmentalists fear that if the EPA agrees with the chemical industry, the decision could have wide implications. It would significantly curb the agency's ability to limit nearly 200 pollutants from thousands of industrial plants. According to EPA estimates, the 2024 revised rule for chemical plants was projected to cut the number of nearby residents exposed to unacceptable cancer risks from 90,000 to 3,000. Ana Baptista, a professor of environmental policy and sustainability management at The New School, criticized the potential shift in policy.

Baptista stated, "It’s a poor reflection on this administration’s claim that they are actually interested in clean air." She added, "By saying we’re no longer going to consider science, it’s abdicating your mission."

The core of the issue lies within the Clean Air Act, the nation's primary law regulating hazardous air pollutants from industrial operations. The law requires the EPA to conduct a residual risk review within eight years of publishing a rule. These assessments use detailed data on emission quantities, chemical toxicity, and dispersion patterns to determine if the emissions pose unacceptable risks of cancer, respiratory diseases, or reproductive harm. If risks exceed legal limits, the agency must tighten the rules.

However, the Clean Air Act does not explicitly state whether the EPA is required to conduct additional residual risk reviews after the first one, nor does it specifically prohibit them. As far back as 2006, the EPA under President George W. Bush asserted that the agency had the right to revisit and revise rules based on risk. In response to the 2021 Inspector General report, the EPA asserted that the Clean Air Act "does not limit our discretion or authority to conduct another risk review should we consider that such review is warranted."

Despite this history, the Trump administration's EPA is now reconsidering this authority. The agency has declined to address specific questions regarding the ethylene oxide reevaluation. Instead, it pointed to a March 2025 press release stating it was reconsidering multiple air pollution rules issued by the previous administration. A spokesperson noted, "EPA is committed to using the gold standard of science during these reviews," and emphasized that providing clean air is a top priority.