By Marian Wang, ProPublica

Chemical compounds from the oil dispersants applied to the Gulf of Mexico didn't break down as expected, according to a study released this week. Scientists found the compounds lingering for months in the deep waters of the Gulf, long after BP's oil had stopped spewing.

"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 scientist David Valentine of U.C. Santa Barbara, one of the investigators in the study.

The findings contrast with what the Environmental Protection Agency has asserted about the dispersants, which the agency allowed BP to use in unprecedented quantities.

"We do have information about the individual components of the dispersant," the EPA says on its website. "The available peer-reviewed literature indicates that the components biodegrade fairly rapidly."

The information about the components in the dispersant, it's worth noting, was provided to the agency by the dispersant manufacturer. As we've pointed out, the EPA also relied on the manufacturer to provide data on the dispersant's toxicity and approved it for use in the Gulf without doing independent testing.

The study's investigators emphasized that the dispersants' effects remain largely unknown.

"We still don't know just how serious the threat is," said Valentine. "The deep ocean is a sensitive ecosystem unaccustomed to chemical irruptions like this."

In the aftermath of the spill, the EPA concluded that the use of dispersants was a "wise decision." Agency scientists had reported that no dispersants were detected in waters near the Gulf shore, according to McClatchy.

The research was funded by the Woods Hole Oceanographic Institution and the National Science Foundation.