While the methane levels from the 2010 Deepwater Horizon oil spill may have returned to normal, the chemical dispersants used during the disaster in the Gulf of Mexico may be here to stay.

According to a study published in the American Chemical Society journal Environmental Science & Technology, a key component of the dispersants, dioctyl sodium sulfosuccinate, was still present in a plume of oil and gas in the deep ocean months after almost 800,000 gallons of chemical dispersants were injected into the flow from the well.

According to David Valentine, professor of geochemistry and geomicrobiology at UCSB and a co-author of the study, the dispersants were released in order to prevent oil from reaching the surface.

[media-credit name=”PHOTO COURTESY OF David Valentine” align=”alignleft” width=”250″][/media-credit]

Tankers containing chemical dispersants are stored at a port facility in the Gulf of Mexico. Nearly 800,000 gallons of the dispersant were applied about a mile underwater to prevent oil from reaching the surface.

“Dispersants were applied subsurface to reduce the amount of oil that reached the surface,” Valentine said in an e-mail. “I have not seen compelling evidence for either success or failure.”

The study is the first peer-reviewed research on the dispersants used in the Deepwater Horizon oil spill as well as the first study that contains data on deep water application of dispersants in general. The researchers found that the compound — also referred to as DOSS — did not show any sign of rapid biodegradation and was instead present in the plumes in concentrations that suggest only dilution occurred.

“This study provides a first critical look at what happened to all that dispersant injected directly into the gush of oil at the sea floor,” Valentine said in a press release. “Key components of the dispersant were trapped in subsurface plumes of oil and gas, and were not rapidly biodegraded.”

Elizabeth B. Kujawinski, a chemist from the Woods Hole Oceanographic Institution and first author of the study, said the lack of biodegradation of DOSS was not expected.

“This study gives our colleagues the first environmental data on the fate of dispersants in the spill. These data will form the basis of toxicity studies and modeling studies that can assess the efficacy and impact of the dispersants,” Kujawinski said in a press release. “We don’t know if the dispersant broke up the oil. We found that it didn’t go away, and that was somewhat surprising.”

According to Valentine, DOSS was chosen by the scientists because it is an active ingredient of the dispersants used in the Gulf spill.

“There was much concern about DOSS in particular, and being as it is one of the active ingredients, it seemed the best target,” Valentine said in an e-mail.

While the lack of decomposition of the DOSS is strange, it should not necessarily be alarming, as DOSS is not especially toxic to most organisms at low concentrations. However, its effects are unknown in corals or deep-sea organisms, prompting the Environmental Protection Agency to plan and begin research pertaining to the ecological implications of the dispersants.

According to Valentine, the full the environmental ramifications of dispersant use in the deep ocean are yet to be determined.

“The decision to use chemical dispersants at the sea floor was a classic choice between bad and worse,” Valentine said in a press release. “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.”