Don aurand vice president and senior scientist at

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to these symptoms. Don Aurand, vice president and senior scientist at Ecosystem Management & Associates, Inc., an environmental con- sulting firm under contract to BP, says dispersants used today are less toxic than their predecessors. During the world’s first major oil spill, caused when the super- tanker Torrey Canyon leaked 24–35 million gallons of oil after striking a reef off Great Britain in 1967, workers used chemical degreasers, industrial detergents, kerosene, and other products to disperse the slick. 15 Those products—never intended for use in oil spills—turned out to be ecologically devastating, Aurand says. In contrast, he says, newer dispersants designed specifi- cally for oil spill response balance maxi- mal effectiveness at breaking up a slick with minimal toxicity on their own. How they achieve that balance can’t easily be assessed, however, because the formula- tions—being trade secrets—are protected against public disclosure. The EPA’s National Contingency Plan Product Schedule 16 shows the Corexit products to be near the bottom of the list of approved dispersants in terms of effectiveness. But Gina Coelho, president of Ecosystem Management & Associ- ates, claims the agency’s efficacy testing methods were flawed. “Several decades of research by industry, academia, and spill response organizations show the Corexit products are the dispersants of choice; they work better on weathered and fresh oil, and you can use them over a range of temperatures,” she says. As far as toxicity goes, a good deal of concern focuses around the effects not of the dispersants alone but in combi- nation with crude oil. Dana Wetzel, a senior scientist and program manager at Mote Marine Laboratory who studies the effects of dispersants on marine life, says that compared with oil’s water-soluble fractions (i.e., the BTEX components), the Corexit products are three orders of magnitude less harmful to marine test organisms including Mysidopsis bahia , Menidia beryllina , and Sciaenops ocellatus . Wetzel based her findings on a compari- son of acute LC 50 values (which reflect the “lethal concentration” required to kill 50% of test organisms) obtained in her laboratory. 17 However, LC 50 values for dis- persed oil were the same as for oil’s water- soluble fractions, Wetzel says. She adds that neither she nor her colleagues in the field have adequately explored dispersants’ sublethal effects, “so we don’t know how the organisms’ dispersant burdens or body burdens for dispersed oil relate to changes in reproduction or immune function.” Mitchelmore points out that LC 50 val- ues for the same dispersant or dispersed oil mixtures vary widely among different spe- cies, and even among different life stages within species: “In the scientific literature you can see orders-of-magnitude differ- ences in Corexit toxicity depending on species and life stages.” For instance, she says, among the 13 approved dispersants listed on the EPA’s National Contingency Plan Product Schedule, 18 Corexit 9500 mixed with number 2 fuel oil is listed as the most toxic to fish, but it’s the sixth most toxic to shrimp.
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