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WASHINGTON-- A new federal study of chemical dispersants used to break up oil in the Gulf of Mexico shows that when mixedwith oil, the dispersant is less toxic to aquatic life than oilalone.

The study also show that when mixed with oil, the dispersantused in the Gulf, Corexit 9500A, is no more or less toxic than oilmixtures with other chemical dispersants approved for use in oilspills.

The Environmental Protection Agency released the study resultsMonday as the Obama administration defended itself againstassertions that officials allowed oil giant BP to use excessiveamounts of chemical dispersants whose threat to sea life remainsunknown.

Congressional investigators charge that the Coast Guardroutinely approved BP requests to use thousands of gallons per dayof Corexit despite a federal directive to use the chemicalsparingly.

The Coast Guard approved 74 waivers over a 48-day period afterthe Environmental Protection Agency order, according to documentsreviewed by the investigators. Only in a small number of cases didthe government scale back BP's request.

EPA Administrator Lisa Jackson said in a statement thatofficials have long acknowledged use of dispersants presentsenvironmental trade-offs. The agency took steps to ensure thatother response efforts were used instead of dispersants anddramatically cut dispersant use in late May, she said.

Dispersants were last used July 19, four days after a temporarycap was placed on the leaking Macondo well, and dispersant usedropped by 72 percent from peak volumes following a joint EPA-U.S.Coast Guard directive to BP in late May, Jackson said.

Paul Anastas, EPA assistant administrator for research anddevelopment, said he was surprised to learn that the mixture ofdispersant and oil was about the same toxicity as the oil alone.That result shows that use of the dispersant 'seems to be awise decision, and that the oil itself is the hazard that we'reconcerned about,' Anastas said. He called the oil that spewed intothe Gulf for nearly three months 'Enemy No. 1.'

While the chemical dispersant was effective at breaking up theoil into small droplets so that it could be more easily consumed bybacteria, the long-term effects to aquatic life are unknown. Thatenvironmental uncertainty has led to several spats between BP andthe government over the use of dispersants on the water's surfaceand deep underwater when oil was spewing out of the well.

Rep. Edward Markey, D-Mass., said more than 1.8 million gallonsof toxic dispersants were used to break up the oil as it came outof the well and after it reached the ocean surface.

(Copyright 2010 by The Associated Press. All Rights Reserved.)

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