The U.S. Environmental Protection Agency plans to revoke and reconsider Chevron’s approval to produce 18 plastic-based fuels, including some that an internal agency assessment found were highly likely to cause cancer.

In a recently filed lawsuit, the federal agency said it had “significant concerns” that the approval order “may have been issued in error.” The EPA gave a Chevron refinery in Mississippi the green light to produce the chemicals in 2022 as part of a “climate-smart” initiative designed to promote alternatives to petroleum, ProPublica and the Guardian reported last year.

An investigation by ProPublica and the Guardian found that the EPA calculated that one of the chemicals known as jet fuel was likely to cause cancer in one in four people exposed to the substance during their lifetime.

The risk from another plastic-based chemical, an additive to marine fuels, was more than a million times higher than the agency normally considers acceptable – so high that, according to a preserved document, anyone who died in the course of his or her life would be expected to Life exposed to this substance developed cancer through a public records request. The EPA did not point out the marine fuel additive’s enormous cancer risk in the document authorizing production of the chemicals. When ProPublica asked why, the EPA said it “accidentally” left it out.

Although the agency is required by law to address unreasonable health risks when it discovers them, the EPA’s approval document, known as a “consent order,” did not include instructions on how the company would address cancer risks or numerous other health hazards posed by the chemicals other than requiring workers to wear gloves.

After ProPublica and the Guardian reported on Chevron’s plan to make the chemicals from discarded plastic, a community group near the refinery in Pascagoula, Mississippi, sued the EPA in the U.S. Court of Appeals for the District of Columbia Circuit. The group Cherokee Concerned Citizens asked the court to overturn the agency’s approval of the chemicals.

As ProPublica and the Guardian raised questions about the plastic-based chemicals for several months, the EPA defended its decision to allow Chevron to produce the chemicals. However, in the application filed on September 20, the agency said it would reconsider its previous position. In a statement accompanying the application, Shari Barash, director of the EPA’s new chemicals division, said the decision was based on “potential deficiencies in the order.”

Barash also wrote that the agency used conservative methods in evaluating the chemicals, which led to an overestimation of the risk they posed. The EPA’s application said the agency wanted to reconsider its decision and further consider “the limitations” of the risk assessment and the “alleged infirmities” identified by environmental groups.

When asked last week for an accurate estimate of the chemicals’ actual risk, the EPA declined to answer, citing pending litigation. The EPA also did not respond when asked why it did not acknowledge that its approval may have been made in error in the months ProPublica asked about it.

Chevron, which has not yet started producing the chemicals, did not respond to a question about their potential health effects. The company emailed a statement saying, “Chevron understands that the EPA has told the court that the agency overestimated the dangers associated with these permits.”

As ProPublica and the Guardian noted last year, making fuel from plastic is in some ways more damaging to the climate than simply making it directly from coal, oil or gas. That’s because almost all plastic is derived from fossil fuels, and additional fossil fuels are used to generate the heat that converts discarded plastic into fuels.

Katherine O’Brien, a senior attorney at Earthjustice who is representing Cherokee Concerned Citizens in the lawsuit, said she is concerned that after revoking permission to make the chemicals, the EPA could reauthorize them to make them, which her clients are leaving behind could be endangered.

“I would say it’s a victory that requires vigilance,” O’Brien said of the EPA’s plan to withdraw its permit. “We are definitely on the lookout for a new decision that would result in the re-approval of these chemicals.”