Ethylene oxide was once considered an inconspicuous pollutant. The colorless gas leaked from a relatively small number of industrial facilities and attracted little public attention.
All that changed in 2016, when the Environmental Protection Agency completed a study that found the chemical to be 30 times more carcinogenic than previously thought.
Government agencies then spent years updating regulations that protect the millions of people most exposed to this compound. In 2024, the EPA approved strict rules requiring commercial sterilizers for medical devices and large chemical plants to reduce emissions of ethylene oxide, which can cause lymphoma and breast cancer.
The EPA was doing what it has done many times before: revising its rules based on new scientific knowledge.
Its ability to perform against many air pollutants is currently under threat.
In secretly leaked government records, President Donald Trump’s Environmental Protection Agency said it was reviewing whether the agency had legal authority to update these rules.
Chemical companies and their trade groups argue that once the EPA has revised hazardous air pollution rules, it cannot be reevaluated to take into account newly discovered hazards.
It doesn’t matter how many decades have passed or new information comes out.
If the EPA agrees, environmentalists fear the decision could have far-reaching implications and could significantly limit the agency’s ability to limit nearly 200 pollutants from thousands of factories. The next time new science reveals that a chemical is far more toxic, or that the amount of pollutants emitted by a factory has been underestimated and may pose a legally unacceptable health risk, government agencies will not be able to react.
“This doesn’t reflect well on the current administration’s claims that they actually care about clean air,” said Ana Baptista, a professor of environmental policy and sustainability management at the New School. “By saying you no longer consider science, you are abandoning your mission.”
EPA did not address ProPublica’s questions about the reassessment of ethylene oxide or its broader impact. Instead, the agency pointed to a March press release about how it was reconsidering several air pollution regulations issued by President Joe Biden’s administration, including for chemical plants and commercial sterilization equipment. “EPA is committed to using the gold standard of science in these reviews,” a spokesperson said in an email. “From day one, EPA has made it clear that providing clean air, water, and land for all Americans is our top priority.”
EPA’s review focuses on the Clean Air Act, the nation’s most powerful air quality law, which regulates harmful air pollutants in many types of industrial operations. For example, there are certain rules for oil refineries and other rules for steel mills. Within eight years of each rule’s publication, EPA must conduct an evaluation called a residual risk review to determine whether updates are needed.
These assessments use detailed data on emissions from each facility, the toxicity of each chemical, and other information about how the chemicals are released and spread into the air. The combined data reveals how emissions put local populations at risk of cancer, respiratory disease, reproductive harm and other health problems.
If EPA determines that the overall risk exceeds the level allowed by law, regulations must be tightened.
The Clean Air Act does not specify whether EPA is required to conduct additional residual risk reviews after the initial residual risk review. Nor does it specifically prohibit agents from doing so.
Under President George W. Bush, the EPA had argued as far back as 2006 that the agency had the right to review and amend rules based on risk.
The issue took on new relevance in 2021 when the EPA’s Office of Inspector General cited new conclusions regarding the toxicity of ethylene oxide. The agency estimated that industrial emissions from chemical plants, commercial sterilization equipment, and other facilities that emit ethylene oxide expose nearly half a million Americans to unacceptable cancer risks.
In its report, the Office of Inspector General recommended that the agency “exercise its discretion to conduct new residual risk studies” as appropriate if “new data and information indicate that air pollutants are more toxic than previously determined.” (The inspector general was an appointee of President Trump.)
EPA already conducted its first mandatory risk reviews for large chemical plants and commercial sterilization equipment in the early 2000s. In response to the Inspector General’s report, the agency launched additional investigations using the latest science on ethylene oxide. Ultimately, the EPA determined that the health risks were unacceptable and revised the regulations to reduce the health risks. The agency argued that the Clean Air Act “does not limit our discretion or authority to conduct a risk review if we believe such a review is warranted.”
The EPA estimates that new regulations for chemical plants under the 2024 rule will reduce the number of nearby residents at unacceptable cancer risk from 90,000 to 3,000.
However, the chemical industry opposed the stricter rules. Industry representatives opposed the EPA’s new assessment of ethylene oxide, arguing that it overestimates the risks posed by the chemical and that the agency lacks the authority to conduct a risk assessment. The American Chemistry Council said in a 2023 letter that “the agency erred in conducting the new risk review” because the “plain text” of the Clean Air Act “indicates that EPA actually lacks this authority.”
Similarly, the Louisiana Chemistry Council submitted public comments on the chemical plant regulations, stating that “EPA has no legal authority to conduct a second risk review” and that doing so would be “arbitrary and capricious.”
David Cresson, the association’s president and CEO, told ProPublica that the industry group supports “protecting public health through a legitimate regulatory framework that is based on sound science.”
American Chemistry Council spokesman Brendan Bradley said the organization had no further comment on the matter.
After President Trump took office, one of his appointees to the Environmental Protection Agency informed the industry that the agency was conducting a “review” of two rules focused on ethylene oxide emissions. Last spring, Principal Assistant Secretary Abigail Tardif, a former oil and gas lobbyist, suggested how the EPA might challenge these rules.
In a letter to industry groups representing commercial sterilizers and chemical plants, Tardif said the agency is reviewing multiple issues related to the rule, including “EPA’s authority and decision to conduct a second residual risk review” under the Clean Air Act, “the analysis and decisions made in that review, and the resulting risk standards.”
Mr. Tardif did not respond to requests for comment.
The agency also filed a regulatory notice regarding its plans to amend the 2024 Chemical Plant Regulations. Citing the portion of the Clean Air Act that deals with the latest regulatory evaluations, the notice stated that EPA has “identified items to be reconsidered with respect to CAA section 112(f)(2) residual risk review authority.”
While the stricter rules for ethylene oxide are technically still in effect, the Trump administration has exempted dozens of large chemical plants and sterilization facilities from complying with the rules, as the agency moves through a formal process that is widely expected to water down the standards.
Even if the Trump Environmental Protection Agency determines it lacks legal authority to conduct multiple risk studies, the agency may still have the authority to use other parts of the Clean Air Act to enforce harmful air pollution regulations, said Abel Russ, senior attorney at the advocacy group Environmental Integrity Project. This section of the law allows the EPA to update the rule if EPA scientists conclude that better pollution control technology is available at an affordable price. But limiting the agency’s ability to conduct residual risk reviews would be a “knee-jerk” on the agency’s authority over these toxic pollutants, and would be a serious blow to the law, Russ said.
If the EPA concludes that it lacks the legal authority to revise harmful air pollution rules multiple times based on risk, environmental groups will almost certainly sue. Russ called the industry’s comments ridiculous and said they do not account for the reality that our knowledge about industrial pollution is constantly changing.
As ProPublica reported in October, the agency recently obtained clear evidence that many industrial facilities are leaking far more pollutants than the companies that own them had previously reported. In 2023, researchers conducting independent air monitoring in an industrial area of Louisiana known as Cancer Alley found much higher concentrations of ethylene oxide than expected. In more than half of the areas they sampled, the local cancer risk from ethylene oxide would be unacceptable if residents were exposed to these concentrations over their lifetime.
If EPA determines that it does not have the legal authority to conduct multiple risk studies, it will be in a position where it cannot take action even if EPA confirms similar results.
“The whole premise of risk assessment is that it’s based on the best available science,” says Kimberly Terrell, a researcher at the Conservation Project. She added that as our knowledge increases, researchers tend to find that chemicals are associated with additional health effects, so blocking these updates “almost guarantees” that the EPA is underestimating the risks.
