Gulf oil spill dispersed, though maybe not for good
The massive use of dispersant chemicals to break up the Deepwater Horizon oil leak may have prevented more serious harm to Louisiana's wildlife and wetlands, but the remedy may actually have caused more subtle long-term harm to less visible but important components of the Gulf of Mexico ecosystem, suggests a University of Maryland researcher.
Carys Mitchelmore, an aquatic toxicologist at UM's Chesapeake Biological Laboratory, told members of the American College of Veterinary Pathologists that corals and anemones on the sea bottom are particularly sensitive to water contaminated with both tiny oil droplets and the dispersant chemicals. The college is meeting in Baltimore through today (Wednesday, Nov. 3).
Roughly 1.8 million gallons of Corexit chemical dispersants were used to break up the oil gushing from the Macondo well drilled by BP off the coast of Louisiana, with nearly 800,000 gallons pumped nearly a mile down to the source of the leak in a novel attempt to disperse sub-surface plumes. Experts evaluating the dispersants during the three-month leak determined they were no more toxic than the oil, and that their uses was warranted to prevent slicks from smearing beaches and wetlands and fatally coating birds and other wildlife.
But tests in Mitchelmore's lab - conducted with the aid of students at St. Mary's College - found water containing chemically dispersed oil affected the growth of one common species of coral, which took up to three weeks to recover from just an eight-hour exposure. Anemones also absorbed more of the toxic polyaromatic hydrocarbon compounds found in oil when it was broken up into tiny droplets, she said.
"Use of dispersants near coral reefs needs close consideration," she said.
In an interview before her presentation, Mitchelmore said dispersing the massive spill may have made it easier for oil-consuming bacteria to get at it, but it also may have exposed zooplankton and phytoplankton to the toxic effects of petroleum.
"A lot of people may think, 'So what?''' she said. "But if you kill those organisms, you're killing the food web." That could have delayed effects on the abundance of marine life, she said, noting that the Gulf is a breeding ground for such valued commercial fish as bluefin tuna.
"We're going to be looking at this for years to come," she said.
Mitchelmore. a co-author of a 2005 report by the National Research Council on oil spill dispersants, has testified repeatedly before Congress this year on the trade-offs and potential risks involved. She noted that despite repeated heavy uses of chemical dispersants to treat large spills - including the largest application in 1979 in another drilling rig blowout in Mexican waters - there are still significant gaps in knowledge about the toxicity of the chemicals used.
(Deepwater Horizon drilling rig fire, April 2010. Coast Guard photo via AP)