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Scientists say they still don't know whether dispersants truly enable bacteria to digest spilled oil more quickly or whether dispersed oil is safer for marine life than untreated slicks.
Bacteria do seem to be digesting the oil in the Gulf of Mexico, according to an Aug. 25 report, but data are mixed on whether dispersants help bacteria along. Mervin Fingas, a retired scientist with the Canadian government, said that of roughly 40 biodegradability studies he surveyed between 1997 and 2008, about 60 percent said dispersant retarded growth of oil-eating microbes and 15 percent reported no effect. The remaining 25 percent noted a positive effect.
But positive findings are open to interpretation. At a 1999 oil spill conference, researchers reported that microbial populations dining on oil treated with the dispersant Corexit 9500 (used by BP in the Gulf) grew more than seven times as large as those eating oil dispersed physically, suggesting the bacteria were helping.
Yet a comprehensive 2005 review of dispersants by the National Research Council concluded that the healthy bacterial growth in such studies could easily be due to microbes feeding on dispersant, not oil. "There is no conclusive evidence demonstrating either the enhancement or the inhibition of microbial biodegradation when dispersants are used," the 12 authors wrote.
This jumble of findings has led to disagreement among experts that might be resolved by careful analysis of real-life cleanups, which hardly ever happens, said Larry McKinney, executive director of Texas A&M University's Harte Research Institute for Gulf of Mexico Studies in Corpus Christi, Texas.
Funding for such studies "waxes and wanes with oil spills, but never seems to follow through," McKinney said. Many investigations were launched after the Ixtoc spill to explore the effects of dispersed oil, he added.
But funding, and science, dried up when the well did.