Ecolab Inc.'s Nalco Holding Co. unit, which provided a dispersant used to deal with the 2010 BP Gulf of Mexico oil spill, has been dismissed from lawsuits over the incident.

BP used the Nalco chemical dispersant to break up oil and reduce the harm to the Gulf Coast following the explosion and sinking of the Deepwater Horizon drilling rig in April 2010. Plaintiffs sued Nalco, claiming the dispersant, called Corexit, was defective and more toxic than the oil itself.

Nalco said the claims for exposure-related injuries were preempted by federal law giving the government authority to direct all actions to remove a substantial spill. U.S. District Judge Carl Barbier in New Orleans agreed, finding Wednesday that the claims were preempted by the U.S. Clean Water Act and the National Contingency Plan, which put the government in charge of the response.

"Nalco did not decide whether, when, where, how or in what quantities Corexit was applied in response to the Deepwater Horizon/Macondo Well oil spill," Barbier said in a 36-page opinion. He also said such claims might harm a response to future spills.

"If the court were to permit" the claims against Corexit, even if the product was found to be defective or dangerous, "then during the next substantial spill or spill of national significance,' the threat of liability might cause the manufacturer of dispersant X to refuse to provide its product," Barbier said.

Barbier said he wasn't considering whether Corexit was toxic or defective, just that the claims against Nalco had to be dismissed as a matter of law.

"We're ecstatic," Michael Monahan, a spokesman for St. Paul-based Ecolab, said Wednesday. "It's a vindication of the position we've had all along."