So far, at least 325,000 gallons of dispersants have been added to the gulf waters to help break up the 5,000 barrels of crude oil that have leaked into the gulf each day since the April 20 explosion that sank the Deepwater Horizon oil rig.
But dispersants don't eliminate the pollution problem, says Carys Mitchelmore, an environmental chemist at the University of Maryland Center for Environmental Science in Solomons. While less toxic than earlier generations of dispersants, the chemicals only succeed in changing which marine and other wildlife are affected -- fewer animals on the beaches and more in other parts of the ocean and at the sea floor, Mitchelmore says in the journal Nature.
"It's a trade-off, and no one will tell you using dispersants won't have an effect," said Mitchelmore, co-author of a 2005 U.S. National Academies report on dispersants. "You're trading one species for another."
In a yet-to-be published study, for example, Mitchelmore and her colleagues found soft corals exposed to crude oil and the Corexit 9500 dispersant currently in use experienced significantly lower growth rates.
"The long-term effects are really unknown," Mitchelmore said. "The dispersant has inherent toxicity. And these oil droplets tend to be the same sort of size as food particles for filter-feeding organisms."
While dispersants had been applied primarily at the ocean surface, robots are being employed to inject them as the oil leaks from the ocean floor a mile deep, a method never tried before and one the Environmental Protection Agency says will have a "still widely unknown" impact on the environment, the Nature article reports.