(Read Part I: Gulf seafood poses long-term health risks and Part II: Heavy metals go untested in Gulf.)

A major potential long-term health concern left in the wake of BP’s catastrophic oil spill is the nearly two million gallons of dispersant sprayed over and pumped into the Gulf, scientists say. Much of it was injected into the sea beneath its surface, which made both the amount used, and its use, unprecedented.

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In interviews, National Oceanic and Atmospheric Administration (NOAA) and FDA officials repeatedly told Raw Story that dispersant “does not bioaccumulate” in seafood and therefore is not toxic to humans. The two dispersants used during the oil spill, Corexit 9527 and Corexit 9500, contain many ingredients “found in common household products.” And even though there is still no chemical test to detect dispersant in Gulf seafood – though officials said one is coming very soon – sensory tests are effective down to one part per million.

Yet when questioned further by Raw Story, both NOAA and FDA officials admitted that the science behind how dispersants used on this scale will actually impact the Gulf ecosystem and food chain is extremely thin.

After Raw Story suggested that little valuable information exists regarding the effect of so much dispersant on fish and shellfish, NOAA toxicologist John Stein first said, “It’s not quite accurate to say that there’s no science.”

But he conceded, “We don’t have it with regard to aquatic species and fish. We don’t have studies with any of the Gulf species,” adding there could be some potential “low risk.”

“We understand that people are concerned about the dispersant,” FDA spokeswoman Meghan Scott told Raw Story in a separate interview. “It obviously was used extensively to disperse the oil.”

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“But we really do believe that the dispersant is not likely to be present in the fish, particularly where there’s no oil present,” Scott continued.

Scott eventually added, “We would like to have a greater depth of knowledge.”

Edward Trapido, the Wendell Gauthier Chair of Cancer Epidemiology at the Louisiana State University School of Public Health, revealed to Raw Story that 2-butoxyethanol, one of the compounds in Corexit 9527 – the first dispersant used by BP – is not only considered a carcinogen by the state of New Jersey, but the NJ Department of Health says “it should be handled as a carcinogen with extreme caution.”

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“Unfortunately,” Trapido added, “there were two dispersants used – 9500 and 9527. They used 9527 first, until the supplies ran out. Then they switched to 9500. But we don’t know how much of the 9527 was used.”

Trapido raised this concern during his testimony in June at a House Subcommittee on Energy and Environment hearing on the spill. He’s heading a research group at LSU that will examine a range of health effects, including psychiatric and behavioral effects, chronic diseases and cancers.

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As part of the research, Trapido said he’s been searching for this information on BP’s use of Corexit 9527 but has yet to find it.

Miriam Rotkin-Ellman, a staff scientist at the Natural Resources Defense Council, a leading national environmental group, believes it’s “premature” to claim that dispersant will have little harm on marine life and people.

She also told Raw Story that noting some of the dispersant ingredients are in common household products is “a false assurance.”

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Ellman, who contributed to last month’s peer-reviewed Journal of the American Medical Association (JAMA) study on Gulf seafood safety, also revealed another chemical activity of dispersant that neither NOAA nor FDA had mentioned to Raw Story.

It’s widely known that the central reason provided by government officials for using the dispersant is to break down oil into smaller pieces, making it more available to oil-eating microbes and thus speeding up the process by which the oil is removed from the ecosystem.

“Dispersant chemicals are effective at breaking the oil down into smaller parts,” she explained. “[But] by breaking it down into smaller pieces, it can more readily be absorbed by aquatic organisms and incorporated into their bodies.”

In other words, Ellman said, there is some literature that says using a dispersant can increase the amount of contamination you might expect in aquatic life because it’s broken the oil down into smaller pieces, which make it easier for animals to absorb.

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“So I think both things can exist at the same time because it’s looking at different aquatic processes.”

Trapido, who lives two blocks away from the Mississippi River in New Orleans, home to a “huge seafood presence,” looks forward to the new chemical test to detect dispersants.

“I’ll feel better when that’s done,” he said.

Brad Jacobson is a contributing investigative reporter for Raw Story.