Editor's note: Lisa Myers' report on oil dispersants will air Friday on NBC Nightly News.
Amid growing concern about the use of dispersants in the Gulf of Mexico, a group of scientists working for law firms suing BP says their testing indicates that the dispersants being used to break up the oil are making this spill even more toxic to marine life.
Dr. William Sawyer, a toxicologist, is part of a team of scientists hired by law firms — led by Smith Stag of New Orleans — that are representing Louisiana fishermen and environmentalists.
The scientists collected and analyzed globs of oil, sand, and water from more than a dozen sites in four states along the Gulf.
Sawyer told NBC News that the findings are troubling. "We now have compelling evidence that the dispersant has enhanced and increased the toxicity from the spill," he said.
Last week, a group of independent scientists called for an "immediate halt" to the use of dispersants. In what was called a "consensus statement," they warned that dispersants pose "grave risks to marine life and human health."
Spreading the damage?
So far, the federal government has approved use of more than 1.8 million gallons of dispersant in the Gulf. Most of it is Corexit 9500.
One reason relatively little oil is now on the surface of the Gulf's waters is the use of such a vast quantity of dispersants. The dispersant spreads the oil over a much larger area, which some scientists worry makes it hard for marine life to avoid it.
Studies also have shown that when the dispersant breaks up the oil, it can free the most toxic components — certain hydrocarbons — and spread them throughout the water, exposing marine animals to more toxic components than if the oil hadn't been dispersed.
Sawyer said their tests show that is now happening in parts of the Gulf. "What we found is a pattern of highly toxic hydrocarbon components that are not normally soluble in seawater, and at levels that are toxic to the marine environment," he said.
Sawyer said these toxic hydrocarbons can be especially harmful to early stages of marine life.
NBC News shared Sawyer's findings with Dr. Moby Solangi, a biologist at the Institute for Marine Mammal Studies, who has studied how oil spills impact marine life.
Solangi called the findings "very concerning." "The way he [Sawyer] has theorized that the toxicity of the combination of both [oil and dispersant] is of some concern — that needs to be looked at very carefully," Solangi said.
Other scientists told NBC that Sawyer's theory appears valid, but can't be proven conclusively without testing the mixture of oil and dispersant on marine life.
A toxic brew
Most recent scientific research has found that combining dispersants with oil makes the oil even more toxic. A review of more than 400 studies since 1997 showed that 75 percent of them found that the combination of oil and dispersant actually increased the toxic effects of the oil.
"I think we all agree that the dispersed oil is more likely to be toxic than the crude oil by itself," says Dr. Joe Griffitt, a toxicologist at the University of Southern Mississippi.
However, so far, the scientific community has not reached any conclusion on whether oil mixed with dispersant is increasing the danger to marine creatures in the case of this particular spill. Part of the problem is that so little is known about use of dispersants in such great amounts or at this depth — 5,000 feet.
BP points out that the federal government has approved its use of dispersants, and that they've been "very effective in keeping oil from reaching shore." BP says it's working closely with the government to monitor the environmental impact, and has committed to spend $500 million over 10 years to study the impact on the Gulf environment.
Nalco, which makes Corexit, says the EPA has concluded that use of Nalco's dispersants "has not significantly affected the marine environment" and that federal officials have said they resulted in "no harm to aquatic life."
The EPA says "no federal agency has said these products cause no harm to aquatic life"," but that its testing so far shows no "significant impact."
Because of potential litigation, the EPA hasn't seen all of Sawyer's data. But the agency says it's now conducting its own tests to determine just how toxic dispersants mixed with oil are to life in the Gulf.
To read statements to NBC News about the use of dispersants from BP, EPA and Nalco, as well as link to a statement from independent scientists opposed to the use of dispersants, click here.