The Environmental Protection Agency approved a component of boat fuel made from discarded plastic that the agency’s own risk formula determined was so hazardous, everyone exposed to the substance continually over a lifetime would be expected to develop cancer. Current and former EPA scientists said that threat level is unheard of. It is a million times higher than what the agency usually considers acceptable for new chemicals and six times worse than the risk of lung cancer from a lifetime of smoking.

Federal law requires the EPA to conduct safety reviews before allowing new chemical products onto the market. If the agency finds that a substance causes unreasonable risk to health or the environment, the EPA is not allowed to approve it without first finding ways to reduce that risk.

But the agency did not do that in this case. Instead, the EPA decided its scientists were overstating the risks and gave Chevron the go-ahead to make the new boat fuel ingredient at its refinery in Pascagoula, Mississippi. Though the substance can poison air and contaminate water, EPA officials mandated no remedies other than requiring workers to wear gloves, records show.