WASHINGTON – A new federal study of chemical dispersants used to break up oil in the Gulf of Mexico shows that when mixed with oil, the dispersant is no more toxic to aquatic life than oil alone.
The study also show that when mixed with oil, the dispersant used in the Gulf, Corexit 9500A, is no more or less toxic than oil mixtures with other chemical dispersants approved for use in oil spills.
The Environmental Protection Agency released the study results Monday as the Obama administration defended itself against assertions that officials allowed oil giant BP to use excessive amounts of chemical dispersants whose threat to sea life remains unknown.
Congressional investigators charge that the Coast Guard routinely approved BP requests to use thousands of gallons per day of Corexit despite a federal directive to use the chemical sparingly.
The Coast Guard approved 74 waivers over a 48-day period after the Environmental Protection Agency order, according to documents reviewed by the investigators. Only in a small number of cases did the government scale back BP's request.
EPA Administrator Lisa Jackson said in a statement that officials have long acknowledged use of dispersants presents environmental trade-offs. The agency took steps to ensure that other response efforts were used instead of dispersants and dramatically cut dispersant use in late May, she said.
Dispersants were last used July 19, four days after a temporary cap was placed on the leaking Macondo well, and dispersant use dropped 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 and development, said he was surprised to learn that the mixture of dispersant and oil was about the same toxicity as the oil alone.
That result shows that use of the dispersant "seems to be a wise decision, and that the oil itself is the hazard that we're concerned about," Anastas said. He called the oil that spewed into the Gulf for nearly three months "Enemy No. 1."
While the chemical dispersant was effective at breaking up the oil into small droplets so that it could be more easily consumed by bacteria, the long-term effects to aquatic life are unknown. That environmental uncertainty has led to several spats between BP and the government over the use of dispersants on the water's surface and deep underwater when oil was spewing out of the well.
Rep. Edward Markey, D-Mass., said more than 1.8 million gallons of toxic dispersants were used to break up the oil as it came out of the well and after it reached the ocean surface.
(This version CORRECTS that dispersants mixed with oil are not more toxic than oil alone, instead of less toxic.)