Ethylene oxide was once considered an unremarkable pollutant. The colorless gas seeped from relatively few industrial facilities and commanded little public attention.
All that changed in 2016, when the Environmental Protection Agency completed a study that found the chemical is 30 times more carcinogenic than previously thought.
The agency then spent years updating regulations that protect millions of people who are most exposed to the compound. In 2024, the EPA approved stricter rules that require commercial sterilizers for medical equipment and large chemical plants to slash emissions of ethylene oxide, which causes lymphoma and breast cancer.
It was doing what the EPA has done countless times: revising rules based on new scientific knowledge.
Now, its ability to do that for many air pollutants is under threat.
In government records that have flown under the radar, President Donald Trump’s EPA said it is reconsidering whether the agency had the legal authority to update those rules.
Chemical companies and their trade organizations have argued that the EPA cannot reevaluate hazardous air pollution rules to account for newly discovered harms if it has revised them once already.
It doesn’t matter if decades have passed or new information has emerged.
If the EPA agrees, environmentalists fear that the decision could have wide implications, significantly curbing the EPA’s ability to limit nearly 200 pollutants from thousands of industrial plants. The next time new science reveals that a chemical is much more toxic, or that the amount of pollution released from a factory had been underestimated and would cause legally unacceptable health risks, the agency would not be able to react.
“It’s a poor reflection on this administration’s claim that they are actually interested in clean air,” said Ana Baptista, a professor of environmental policy and sustainability management at The New School. “By saying we’re no longer going to consider science, it’s abdicating your mission.”
The EPA didn’t address ProPublica’s questions about the ethylene oxide reevaluation or its broader implications. Instead, the agency pointed to a March press release about how it was reconsidering multiple air pollution rules issued by President Joe Biden’s administration, including the ones for chemical plants and commercial sterilizers. “EPA is committed to using the gold standard of science during these reviews,” a spokesperson said in an email. “Since day one, EPA has been clear that providing clean air, water, and land for all Americans is a top priority.”
The EPA’s reconsideration focuses on the Clean Air Act, the country’s most powerful air quality law, which regulates hazardous air pollutants for different types of industrial operations. There’s a specific rule for oil refineries, for instance, and another for steel mills. Within eight years after each rule is published, the EPA is required to conduct an assessment, called a residual risk review, to decide if an update is necessary.
These assessments use detailed data on the quantity of emissions coming from each facility, the toxicity of each chemical and other information on how the chemicals are released and dispersed in the air. The combined data reveals how the emissions put local residents at risk of cancer, respiratory diseases, reproductive harm and other health problems.
If the EPA determines the overall risks exceed what’s allowed under the law, the agency must tighten the rules.
The Clean Air Act doesn’t say whether the EPA is required to conduct additional residual risk reviews after the first one. Nor does it specifically prohibit the agency from doing so.
As far back as 2006, the EPA under President George W. Bush asserted that the agency had the right to revisit and revise the rules based on risk.
The issue became newly relevant in 2021, when the EPA’s Office of Inspector General cited the new conclusions about the toxicity of ethylene oxide. The office estimated that nearly half a million Americans were exposed to unacceptable cancer risks from industrial emissions by chemical plants, commercial sterilizers and other facilities pumping out ethylene oxide.
In its report, the inspector general’s office advised the agency to “exercise its discretionary authority to conduct new residual risk reviews” as needed when “new data or information indicates an air pollutant is more toxic than previously determined.” (The inspector general was a Trump appointee.)
The EPA had already conducted the first, mandatory risk reviews for large chemical plants and commercial sterilizers in the early 2000s. In response to the inspector general report, the agency launched additional reviews using the updated science on ethylene oxide. Ultimately, the EPA determined the health risks were unacceptable and revised the rules to lower them. The agency 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.”
According to the EPA’s estimates, the new regulations for chemical plants under the 2024 revised rule would cut the number of nearby residents who are exposed to unacceptable cancer risks from 90,000 to 3,000.
But the chemical industry opposed the stricter rules. Industry representatives disagreed with the EPA’s new assessment of ethylene oxide, contending that it overestimated the risk the chemical posed, and argued the agency didn’t have the authority to conduct those risk reviews. In a 2023 letter, the American Chemistry Council said “the Agency has erred in conducting a new risk review,” as “the plain text” of the Clean Air Act “indicates that EPA actually lacks this authority.”
Similarly, the Louisiana Chemical Association submitted public comments on the chemical plant rule stating the “EPA has no statutory authority to conduct a second risk review” and that doing so was “arbitrary and capricious.”
David Cresson, president and CEO of the association, told ProPublica that the trade group supports “protecting the public’s health through regulatory frameworks that are lawful, while remaining based in sound science.”
Brendan Bradley, a spokesperson for the American Chemistry Council, said the organization had no further comment on the issue.
After Trump was inaugurated, one of his appointees to the EPA let the industry know the agency was conducting a “reconsideration” of the two rules focused on ethylene oxide emissions. Last spring, Principal Deputy Assistant Administrator Abigale Tardif, a former oil and gas lobbyist, hinted at how the EPA might challenge those rules.
In letters addressed to trade groups representing commercial sterilizers and chemical plants, Tardif said the agency was reconsidering multiple issues related to the rules, including the “EPA’s authority and decision to undertake a second residual risk review” under the Clean Air Act, as well as “the analysis and determinations made in that review, and the resulting risk standards.”
Tardif didn’t respond to requests for comment.
The agency also filed a regulatory notice about its plans to revise the 2024 chemical plant rule. Citing the part of the Clean Air Act that deals with the updated rule assessments, the notice said the EPA had “identified items for reconsideration around its CAA section 112(f)(2) residual risk review authority.”
While the stricter ethylene oxide rules are technically still in effect, the Trump administration has exempted dozens of large chemical plants and sterilizer facilities from following them as the agency works through a formal process that is widely expected to result in watered-down standards.
If the Trump EPA does decide it lacks the legal authority to conduct multiple risk reviews, the agency might still have the authority to strengthen hazardous air pollution rules by using a separate part of the Clean Air Act, said Abel Russ, a senior attorney at the Environmental Integrity Project, an advocacy group. That section of the act allows the EPA to update a rule if agency scientists conclude that better pollution-control technology is affordable and available. But limiting the agency’s ability to conduct residual risk reviews would be a serious blow to the act, Russ said, “kneecapping” the agency’s authority over these toxic pollutants.
Environmental groups will almost certainly sue if the EPA concludes it does not have the legal authority to revise hazardous air pollution rules more than once based on risk. Russ called industry’s comments absurd and said they don’t account for the reality that our knowledge of industrial pollution is changing all the time.
As ProPublica reported in October, the agency recently received clear evidence that many industrial facilities are leaking far more pollution than the companies that own them previously reported. In 2023, researchers who conducted their own air monitoring in the industrial corridor of Louisiana known as Cancer Alley found much higher concentrations of ethylene oxide than expected. For more than half the areas they sampled, the local cancer risk from ethylene oxide would be unacceptable if residents were exposed to these concentrations over a lifetime.
If the EPA decides it lacks the legal authority to conduct multiple risk reviews, it would find itself in the position of not being able to take action even if the agency confirmed similar results.
“The whole premise of risk assessment is that it’s based on the best available science,” said Kimberly Terrell, a research scientist at the Environmental Integrity Project. As our knowledge grows, researchers tend to find that chemicals are linked to additional health effects, she added, so blocking these updates “pretty much ensures” the EPA is underestimating the risks.
