WASHINGTON — A study using two sensitive Gulf species shows that the chemical dispersant used by BP in the Gulf, when mixed with oil, was less toxic than the oil itself, the Environmental Protection Agency said Monday.
The test results were released as the Obama administration defended itself against assertions that officials allowed BP to use excessive amounts of dispersants.
The EPA said it tested eight available dispersants — including the one used by BP, known as Corexit 9500.
When mixed with oil, Corexit is also less toxic or no more toxic on the two Gulf species tested — a shrimp and a small fish — than other available chemicals that could be used as an alternative, the EPA stated. Juvenile shrimp and fish were used since they are more sensitive to chemicals than adults.
"Dispersants were less toxic than oil or oil-dispersants mixture," Paul Anastas, EPA's assistant administrator for research and development, told reporters.
Anastas 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."
Anastas added that the EPA, not BP, funded the study.
Last weekend, congressional investigators reported that the Coast Guard routinely approved BP requests to use large amounts of Corexit despite federal directives to use it 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 requests.
EPA Administrator Lisa Jackson said in a statement that officials long have acknowledged use of dispersants presents environmental trade-offs. The agency acted to ensure 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 dropped by 72 percent from peak volumes following a joint EPA-U.S. Coast Guard directive to BP in late May, Jackson said.
While the chemical dispersant was effective at breaking up the oil into small droplets to be consumed more easily 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.
Some experts hired by groups planning to sue BP have said they now have evidence that the dispersants when mixed with oil do have a highly toxic effect.
The congressional inquiry was spearheaded by Democratic Rep. Edward Markey, who 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.
The Associated Press contributed to this report.