Researchers discuss dispersants

By Brian Woodham

Shortly after the Deepwater Horizon rig sank roughly a mile below the water’s surface and BP discovered oil leaking from its wreckage, criticism began swirling about BP’s use of the dispersants Corexit 9500 and 9527, chemical cocktails that break crude oil into globules, dispersing it below the surface and throughout the water column.

Two Auburn U. researchers, Dr. Cliff Lange, associate professor of civil engineering, and Dr. Prabhakar Clement, Arthur H. Feagin Chair of civil engineering, are working on characterizing the nature of the crude oil coming onshore in Alabama. They are conducting tests to determine how much of the dissolved compounds are in the water, how biodegradable they are and how the oil plumes spread with and without dispersants.

According to David Biello’s article in Scientific American, BP ceased using Corexit 9527 after it was deemed to be too toxic. Corexit 9527 contains the organic solvent 2 butoxyethanol, which is a butyl ether of ethylene glycol, or antifreeze.

Lacking this organic solvent, Corexit 9500 is still being used by BP, although in smaller quantities.

BP has reduced its application of dispersants by 68 percent since the EPA issued a directive May 26 calling on BP to cut dispersant use by 75 percent, eliminate surface application and limit subsurface application to less than 15,000 gallons a day.

As of July 1, BP has used more than 1.62 million gallons of dispersant, including more than 590,000 gallons applied subsurface.

“If you look at the way they’re introducing the dispersant,” Clement said, “they’re actually introducing it subsurface, basically, below the water column close to the vent as the oil gushes out, which is actually a good practical strategy if you want to disperse the oil over the water column, which is a questionable strategy, because once the oil comes and goes to the top, it’s viscosity would change, and then it’s really hard to disperse it.”

According to a press release on June30 by EPA Assistant Administrator Paul Anastas, the EPA’s first round of toxicity testing, which tested eight dispersants including Corexit 9500, found that “all of the dispersants are roughly equal in toxicity, and generally less toxic than oil” and that “none of the eight dispersants tested displayed biologically significant endocrine disrupting activity.”

“There are a lot of people in the media discussing the fact that we should use more non-toxic dispersant,” Lange said. “They’re kind of missing the fact that we probably shouldn’t be using dispersant at all. I think a lot of people think ‘out of sight, out of mind.’

“We’re totally neglecting the fact that a majority of the oil could now be underwater where we can’t see. It’s hard to track; it’s interacting with completely different populations; it just changes the whole transport and the fate of the oil.”

Further EPA testing will attempt to determine how toxicity is affected when Louisiana crude and dispersant mix.

“There have been studies that show if you look at the toxicity of the oil itself and toxicity of the Corexit, it’s much less than when you put the two things together,” Lange said, ”so you get this synergistic effect which really amplifies the toxicity.”

Dispersant use is regularly portrayed as an acceptable “tradeoff” between the risks attached to dispersants’ poorly understood toxicity to marine life and the risks of larger impacts from surface oil slicks along the Gulf Coast’s shores, wetlands and marshes. The use of dispersants changes the nature of the oil, making it more available to organisms that are not on the surface, said Lange, who added that tests have shown Corexit bioaccumulates to a small degree up the food chain.

“The other half that a lot of people seem to be missing,” Lange said, “is the fact that you’re changing the nature of the oil and you’re making the oil itself much more available to organisms that aren’t on the surface.”

After conducting chemical analyses of “mousse” samples from Gulf Shores, Lange said he found that all of the light-end hydrocarbons normally found in crude are gone, while the heavy hydrocarbons remain, which are harder to biodegrade.

“They’re the thicker things that stick to everything,” he added. “You’d be surprised that crude itself is very liquidy. It almost looks like water or gasoline: it flows. But what’s coming ashore is almost like chocolate mousse in consistency, very thick.”

Lange explained that without dispersant application, crude typically rises to the surface, where it will mix with water, essentially becoming waterlogged. When the crude gets heavy enough, it sinks.

Lange also explained how non-dispersed and dispersed oil are affected by water currents and wind.

“When it’s on the surface, it’s much more wind-driven, so if the wind blows onshore, you would get more onshore,” Lange said. “When it gets into the water column, it’s driven by major currents, and that’s why we’re worried about it skirting around Florida and coming up the East coast.

“What we’re really doing by adding those things (dispersants),” Lange continued, “is we’re allowing it (the oil) to spread a lot more into places where it normally wouldn’t spread.”

Lange said that some of the dispersed oil will settle to the bottom, where it will slowly biodegrade.

“When it’s on the beach, it degrades differently than when it’s at the bottom of the ocean in these tar balls,” Lange said, adding that those could persist for hundreds of years.

Hurricanes’ ability to push large amounts of water and possibly flood shorelines with oil concerns Lange. The dispersed oil that has settled to the bottom may also be a long-term problem, Lange said.

“We can clean up the beaches,” Lange said, “and then in a couple years, we might get a hurricane come through, mix this stuff up, and it’ll all come in.”

Lange and Clement are also looking at the feasibility of using bioremediation techniques to treat the oil once the leak has been stopped. Bioremediation involves introducing nutrients like nitrates and phosphates to promote bacterial growth along the beaches, which oxidizes and breaks down the hydrocarbons, said Clement.

“The nice thing about using bacteria to bioremediate is that you can spread them out. It’s pretty easy to disperse and treat a large area,” Lange said. “The bad thing is that it doesn’t really work when you get that thick coating of goo.”

A computer code developed by Clement for the Pacific Northwest National Lab in Washington could be adapted to model the oil spill remediation process, Clement said.

RT3D (Reactive Transport in Three Dimensions) is a computer code that allows researchers to design remediation methods and simulate natural degradation processes that help to bioremediate groundwater plumes, he added.

“The chemistry and the physics of this groundwater remediation process is similar to oil spill remediation,” Clement said. “But when you talk about an oil spill, it has unrefined hydrocarbons, so it’s going to be a lot harder problem to deal with.”

Lange explained that the dispersed oil plumes will defeat containment booms and skimmers deployed to protect the Gulf Coast’s shores, marshes and wetlands.

“It’ll go right under (the booms) because (dispersed crude) wants to be in the water, and most booms are allowed to let water go underneath, and just skim the surface,” Lange said. “It will also defeat the surface skimmers.”

“That’s what they should have done in the first place,” Lange said, when asked whether cleanup efforts should focus more on skimming efforts instead of dispersant use, adding “Now that the genie’s out of the bottle, it’s so big that you just can’t physically skim that all off.

“I think right now, we’re in the phase where we’re just doing damage control on this one,” Lange said. “What we really need to be doing is learning from it, so if it does happen again, we understand what to do.”

Read more here:
Copyright 2022 The Auburn Plainsman