Oil from BP s blown-out well has stopped flowing into the Gulf of Mexico and so far there is little sign of the 1.8 million gallons of dispersants used to combat the oil slick.

But experts say very little is known about what their long-term effects might be, either on the creatures living in the Gulf of Mexico or the people who eat them.

Test results released by the Environmental Protection Agency on Monday showed that Corexit 9500, the main dispersant used, is less toxic to some sensitive species of sea life than Louisiana sweet crude oil and that oil and dispersant mixture is no more toxic than oil by itself.

And the dispersants themselves have not been found in any near-shore species of fish, and would be unlikely to pose a health risk in seafood, according to the Food and Drug Administration.

"The constituents of dispersants are highly unlikely to get into the flesh of the fish," said the FDA's Don Kraemer.

However, a panel of scientists testifying at a Senate hearing on Wednesday cautioned that the long term effects of dispersants, particularly on deep sea life, are largely unknown.

"A massive ecotoxicological experiment is underway," Ronald Kendall, director of the Environment and Human Health Institute at Texas Tech University, told the Environment and Public Works Subcommittee on Oversight.

The panel largely agreed the EPA tests left large gaps in knowledge about how dispersants might affect animals in the long term. While the chemicals may not accumulate in the flesh of fish, they might interact with chemicals from the oil that can build up in sea life higher on the food chain. For instance, dispersants might prevent bacteria from breaking down cancer-causing compounds called polycyclic aromatic hydrocarbons, or PAHs, said Richard Denison, a senior scientist with the Environmental Defense Fund.

Little is known about how dispersants could affect PAHs, said Kraemer.

"There is some literature out there and frankly it's very sketchy," Kraemer said in a telephone interview.

Current seafood testing will find whatever PAHs do get into seafood, he said. So far the levels of PAHs that have been found are far below levels considered dangerous by the FDA.

The experts recommended more extensive toxicity testing for dispersants before they are approved for use.
"I look at the dispersants and right now there's very limited information to a point where we can't even evaluate the potential environmental toxicology," Kendall said.

Denison said there is nothing new about having experts say they know little about the effects of dispersants on oil spills.

Studies as early as 1989 from the National Academy of Sciences identified a lack of knowledge and need for research.

Denison said there are often calls for better research after a major oil spill.

"Those calls have often resulted in a little spurt of money being put in and drying up once the interest in the spill disappears," he said.

Studies started after the 1979 Ixtoc oil well blew out off the coast of Mexico failed to come to any conclusions, expert say.

Last week Congress said BP used more dispersants to battle the spill than the EPA had directed.