A US federal judge ruled Monday that the Environmental Protection Agency (EPA) must update its policy on the use of toxic chemical dispersants to clean up oil spills.

The guidance detailed in the National Contingency Plan (NCP) has not been updated since it was published in 1994, and environmentalists have been petitioning to update the law policy since 2012. Subsection J of the NCP currently permits the use of chemical dispersants in catastrophic offshore oil spills, including the Exxon-Valdez and BP spills along the Gulf of Mexico. These chemicals have shown to be more dangerous to humans when combined with oil than the spilled petroleum alone.

Dr. Riki Ott, a marine toxicologist for one of the lawsuit’s lead plaintiffs, described the impact of dispersants on responders and nearby communities, saying, “In 1989, Exxon Valdez response workers called the ubiquitous cold- and flu-like symptoms among frontline workers the Valdez Crud . . . it turned out that these symptoms were early warnings of chemical illnesses that often led to disabling diseases, cancers and early deaths.”

Tuesday’s ruling on the EPA’s motion for summary judgment concluded that the agency violated its duty under the Clean Water Act to maintain guidelines consistent with current science and technology. US District Court Judge William Orrick also found that the EPA’s delay in publishing updates to this rule was a violation of the Administrative Procedure Act.

The EPA must now adjust the NCP oil spill cleanup guidelines to include scientific data and recommendations on the use of dispersants before May 31, 2023. The agency will also have to file status update reports with the court every six months.