Deep-sea chemical dispersants weighed for cleanup of Gulf of Mexico oil spill

Oil companies stress one another's failures in a Senate hearing as cleanup and containment efforts continue in the Gulf of Mexico, after the explosion of the Deepwater Horizon oil rig April 20.
By Juliet Eilperin
Monday, May 10, 2010

The decision on whether to use chemical dispersants deep below the sea's surface to break up the Gulf of Mexico oil spill boils down to two central questions: Is it worth taking this unprecedented step to protect the region's sensitive and ecologically valuable wetlands, even at the potential expense of its marine life? And because the scientific literature on this question is so sparse, should federal officials conduct extensive new research before making the leap?

"It's sort of the devil you know versus the devil you don't," said Linda Greer, a senior scientist at the Natural Resources Defense Council. "It's really shocking to me how little research has been done into these basic questions."

Responders to the downed Deepwater Horizon rig have spent days applying more than 253,000 gallons of oil dispersant -- Nalco's Corexit 9500 -- to break up the tens of thousands of gallons of oil that have reached the ocean's surface.

But these compounds have never been used at depth. Federal officials have conducted two rounds of tests to determine dispersants' effects hundreds of feet underwater, and they are consulting with state and federal agencies as well as local community leaders before making a decision to proceed.

On a basic level, dispersants work the same way dishwashing liquid works on grease: They break up the oil into tiny droplets by attaching to the oil, which then becomes diluted in the water. Scientists and policymakers agree that the oil from the spill poses a greater threat to wildlife and vegetation than the chemicals in the dispersants.

"You're putting something into the water, it's less toxic than the oil, so it's a trade-off," said Coast Guard Commandant Thad Allen, national incident commander for the BP spill, in an interview.

But the question of the broader trade-off -- whether these compounds will wreak havoc on the marine system over time -- remains unanswered. Five years ago, the National Academy of Sciences issued a nearly 400-page study on oil dispersants, which cautioned that "the current understanding of key processes and mechanisms is inadequate to confidently support a decision to apply dispersants."

The NAS panel urged additional scientific inquiry into the matter, but little of that research has taken place. And now, the federal government will have to make a significant decision without it.

The Environmental Protection Agency is analyzing water samples taken from deeper areas in the gulf where responders have applied the dispersants, according to federal officials, and will report back before a broader application takes place.

"It's a hard call," said Carys L. Mitchelmore, one of the authors of the 2005 NAS report and an associate professor at the University of Maryland Center for Environmental Science's Chesapeake Biological Laboratory.

Applying dispersants at depth could kill fish larvae -- such as those from the imperiled Atlantic bluefin tuna that use the Gulf of Mexico for spawning grounds -- and threaten filter-feeders, such as whale sharks, that pass through those waters. It could also harm commercially valuable oysters and mussels, as well as organisms low on the food chain that sustain larger marine creatures. "You would be killing off their food," Mitchelmore said.

There are other unknowns: Almost no research has been done on whether the dispersants will undermine the water repellency of birds, which is essential for regulating their body temperature. And most of the testing has been conducted in laboratories rather than in the field, which might mean that scientists have underestimated the toxic threat a mixture of oil and chemicals could pose. New research suggests that natural light enhances oil's toxicity, Mitchelmore said, which would threaten translucent organisms such as fish larvae.

In addition, Greer said, scientists do not know whether chemically treated oil degrades as quickly as oil that's dispersed through wind and wave, and if it's more toxic.

David Horsup, Nalco's division vice president for energy services research, said that dispersed oil at the surface did degrade more quickly and that the initial results of applying it at depth were "very encouraging."

When it comes to treating an oil spill, he added, "it's not a panacea by any means. It's a very good method, not the only one, and it has to be used in conjunction with other tactics."

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