Chemical dispersants that BP injected directly into its damaged wellhead in the Gulf of Mexico last year, had still not degraded three months after they were applied, according to the first peer-reviewed research on the fate of the chemicals, published Thursday.

Oil streaks on the Gulf of Mexico near the Deepwater Horizon blowout off the coast of Louisiana. [Environment News Services]

In the effort to manage the massive Deepwater Horizon oil spill, BP injected some 771,000 gallons of the chemical dispersant Corexit 9500 a mile beneath the surface of the Gulf of Mexico. Dispersants function like detergents to break up oil into small droplets that mix easily with water.

Woods Hole Oceanographic Institution chemist Elizabeth Kujawinski and her colleagues reported that a major component of the dispersant was contained within an oil and gas-laden plume in the deep ocean and had still not degraded three months after it was applied.

"This study gives our colleagues the first environmental data on the fate of dispersants in the spill," said Kujawinski, who led a team that included scientists from UC Santa Barbara. "We don't know if the dispersant broke up the oil," she said. "We found that it didn't go away, and that was somewhat surprising."

The study, which appeared online today in the American Chemical Society journal "Environmental Science & Technology," is the first peer-reviewed research to be published on the dispersant applied to the Gulf spill and the first data on deep application of a dispersant, according to ACS and Kujawinski.

Previous studies had indicated that dispersants applied to surface oil spills can help prevent surface slicks from endangering marshes and coastlines.

The study was not aimed at assessing the possible toxicity of the lingering mixture. Kujawinski said she would "be hard pressed to say it was toxic."

Still, she said, the results warrant toxicity studies into the effects of the dispersant on corals and deepwater fish such as tuna. The EPA and others have already begun or are planning such research, she said.

Researcher David Valentine of UC Santa Barbara said, "The decision to use chemical dispersants at the sea floor was a classic choice between bad and worse. And while we have provided needed insight into the fate and transport of the dispersant we still don't know just how serious the threat is. The deep ocean is a sensitive ecosystem unaccustomed to chemical irruptions like this, and there is a lot we don't understand about this cold, dark world."

"The good news is that the dispersant stayed in the deep ocean after it was first applied," Kujawinski said. "The bad news is that it stayed in the deep ocean and did not degrade."

"The results indicate that an important component of the chemical dispersant injected into the oil in the deep ocean remained there, and resisted rapid biodegradation," said Valentine, whose team collected the samples for Kujawinski's laboratory analysis.