Mixed results shown from dispersants in BP spill

Seth Borenstein, Associated Press Yahoo News 27 Jan 11;

WASHINGTON – Dispersants injected deep in the Gulf of Mexico to counter an oil gusher last spring seemed to keep some oil from fouling the water's surface, but the chemicals lingered underwater, raising concerns about long-term problems, a new study found.

The first extensive research into what happened to 770,000 gallons of dispersants used a mile deep near the busted BP well found a mixed bag of results. The new research appears in the journal Environmental Science & Technology and focused on the fate of the controversial chemicals rather than their toxicity.

Scientists at the Woods Hole Oceanographic Institution in Massachusetts found circumstantial evidence that the chemicals guided some oil into underwater currents, stopping it from bubbling up to the surface, where it would do more damage, said marine chemist Elizabeth Kujawinski.

That would be considered a good thing, keeping marshes and beaches from getting more tarred, Kujawinski said.

But she added, "the dispersant is sticking around," which is worrisome. The chemicals didn't seem to biodegrade the oil and gas as fast as basic chemistry would predict. Her study said the key chemicals in dispersants underwent "negligible or slow rates of biodegradation." Other studies have found that the oil — not the dispersant — broke apart quickly.

How fast chemicals degrade is important because of potential long-term damage from chronic contamination, she said.

And when it comes to the basic question of whether using the dispersants worked, Kujawinski said it is still too early to tell.

Larry McKinney, who directs a Gulf of Mexico research center at Texas A&M University in Corpus Christi, said the government's use of the chemicals was "successful in avoiding the most serious damage to wetlands marshes. That did work. But there's likely a price to be paid for that success."

A federal study last year found that in the short term, dispersant is no more dangerous to aquatic life than oil. However, the long-term effects to aquatic life remain unknown.

The new study illustrates how little scientists know about using dispersants in deep water, said Florida State University marine scientist Ian MacDonald.

Deep-Sea BP Spill Disperants Didn’t Degrade for Months
Janet Raloff Wired Science 27 Jan 11;

Nearly 3 million liters (some 771,000 gallons) of a chemical dispersant ejected into oil and gas from BP’s Deepwater Horizon oil spill last spring and summer lingered until at least September, a new study shows. The chemicals moved in concert with plumes of oil deep beneath the Gulf of Mexico’s surface.

sciencenewsDavid Valentine of the University of California, Santa Barbara and his colleagues periodically sampled plume water that flowed at depths of 1,000 meters or more between May and September 2010. They shipped these samples to chemist Elizabeth Kujawinski at the Woods Hole Oceanographic Institution in Massachusetts and her colleagues for analysis.

With rare exception, they report online January 26 in Environmental Science & Technology, the dispersant did not degrade but instead moved with the plumes until they were lost to dilution in the Gulf’s depths.

“If the dispersant worked, it should have been associated with the liquid oil — that is, moving off laterally into the deepwater plume. Which is where we found it — and the only place,” Kujawinski says. “We did not see it below the plume or even sloughing off the top of it.”

To scout for the dispersant, known as Corexit 9500A, Kujawinski focused on an active ingredient known as DOSS, or dioctyl sodium sulfosuccinate. It accounted for 10 percent by weight of the dispersant mixture, which was released at rates ranging from around 13,000 to 80,000 liters per day.

Prior to capping the well, plume concentrations of DOSS hovered in the low parts per million range, after which it diminished to parts per billion concentrations. DOSS levels in the plume matched what would have been expected if the dispersants remained with the oil. That, Kujawinski says, suggests no biodegradation of DOSS — and shows why remnants of dispersant applications could be detected 300 kilometers from the wellhead and even two months after their last application.

“When you read about Corexit, it’s supposed to biodegrade,” observes Carys Mitchelmore of the University of Maryland’s Center for Environmental Science in Solomons. But specific rates have not generally been reported, she adds. So the dispersant’s apparent persistence in the new paper is somewhat unexpected.

Then again, Mitchelmore notes, “Corexit is made up of multiple chemicals, so each might have different biodegradation rates.” The aquatic toxicologist says she would like to see are data showing whether Corexit enhanced the ultimate breakdown of BP’s oil.

“The jury’s still out on the role of dispersants in oil degradation,” she says. “Some say they enhance it, others say they inhibit it.”

Like Mitchelmore, Beth McGee of the Chesapeake Bay Foundation in Annapolis, Md., served on a 2005 National Academy of Sciences assessment of oil-spill dispersants. Clearly, McGee says, undersea use in the Deepwater Horizon spill constitutes “uncharted territory.”

“Dispersants typically degrade fairly rapidly,” McGee says. “So the new data leave me fairly surprised.” And, she adds, the results suggest that novel uses — such as injecting them a mile below the surface where it’s cold and there’s no light — deserve study, if only to answer questions prompted by the BP spill.