Chemical dispersants an unknown quantity in addressing oil spill
Thursday, May 6, 2010; 5:18 PM
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 should federal officials conduct extensive new research before making the leap, since the scientific literature on this question is so sparse?
"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 already 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.
Cal Dooley, president of the American Chemistry Council, said Wednesday that chemical companies "have taken extraordinary steps to increase our dispersant production and institute new coordination measures to meet the need. Other chemistry products with potential applications include detergents and absorbents. We applaud these companies' prompt action and strong commitment in addressing this challenge."
But these compounds have never been used at depth: Federal officials have conducted two rounds of tests to determine what effect they would have hundreds of feet underwater, and are consulting with state and federal agencies as well as local community leaders before making the decision to proceed with that line of attack.
On a basic level these dispersants work the same way dishwashing liquid works on grease: They break up the oil into tiny droplets by attaching to the oil so it's diluted in the water column. And scientists and policymakers agree that the oil from the spill poses a greater threat to wildlife and vegetation than the chemicals contained 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, "In many instances where a dispersed plume may come into contact with sensitive water-column or benthic organisms and populations, the current understanding of key processes and mechanisms is inadequate to confidently support a decision to apply dispersants."
The NAS panel urged addition 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.
"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. "There really is very little information and research about what are going to be the environmental consequences. But the trade-off is protect the shoreline at all costs."
David Horsup, Nalco's division vice president for energy services research, said independent laboratories have tested the ecological effects of applying its product on the sea surface, and that its current incarnation "has more favorable environmental properties than what we used 15, 20 years ago." But he added, "Do any of these test conditions simulate subsea conditions? I don't know."
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.
By applying them at depth, Mitchelmore explained, responders will have a better chance of keeping the oil from reaching the marshes on which so many species depend, but they will be exposing organisms "that wouldn't be normally exposed" to both the oil and the chemicals in the dispersants.
That could kill off fish larvae -- such as those from the imperiled Atlantic bluefin tuna that use the Gulf of Mexico for spawning grounds -- and threaten filter-feeders like 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 of dispersants has been conducted in laboratories rather than in the field, which may mean scientists have underestimated the toxic threat a mixture of oil and chemicals could pose. New research suggests 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 if chemically treated oil will degrade as quickly as oil that's dispersed through wind and wave, and if it's more toxic. That could mean the oil will stay in the marine ecosystem longer and exact a higher cost over time. "There's sort of no way to win here," she said.
Horsup, however, said dispersed oil at the surface did degrade more quickly, and "the initial results" of applying it at depth "are very encouraging."
"You always have to compare it against the case of doing nothing," he said. 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."