The decision comes after a ProPublica investigation revealed that the EPA had found that one of the fuels had a cancer risk more than 1 million times higher than the agency usually considers acceptable.

The U.S. Environmental Protection Agency is planning to withdraw and reconsider its approval for Chevron to produce 18 plastic-based fuels, including some that an internal agency assessment found are highly likely to cause cancer.

In a recent court filing, the federal agency said it “has substantial concerns” that the approval order “may have been made in error.” The EPA gave a Chevron refinery in Mississippi the green light to make the chemicals in 2022 under a “climate-friendly” initiative intended to boost alternatives to petroleum, as ProPublica and The Guardian reported last year.

An investigation by ProPublica and The Guardian revealed that the EPA had calculated that one of the chemicals intended to serve as jet fuel was expected to cause cancer in 1 in 4 people exposed over their lifetime.