JIM LEHRER: On the spill, there are also questions about some of the substances that are being used to break up the oil in the Gulf.
NewsHour correspondent Spencer Michels reports from near Buras, Louisiana.
SPENCER MICHELS: Churning his 21-foot boat through the waters near the Gulf of Mexico, 60 miles south of New Orleans, Captain Ryan Lambert is angry. His fishing guide service is essentially dead in the water because of the oil spill. And he's even more worried that chemicals sprayed into the Gulf waters to disperse the oil, nearly two million gallons, will haunt this amazingly beautiful and bountiful bayou country for years.
RYAN LAMBERT, Cajun Fishing Adventures: Well, it's doing exactly what they want it to do. It's sinking the oil out of sight, out of mind. You know, that's -- dispersant is to disperse it and to sink it down. But when it goes under, how long are we going to have to clean it up? How many years will it come in because it will be coming from the depths?
SPENCER MICHELS: But not everyone shares Lambert's fears. At the farmers market in New Orleans, you can still find shrimp fresh caught and for sale. The shrimp seller here, whose husband catches the fish she markets, was thankful for anything that helped get rid of the oil that was ruining their business.
WOMAN: I like to see the oil gone, whichever way they want to do it, but I really don't have the information as far as the dispersant on good or bad. As long as it doesn't hurt anything, it's fine with me.
SPENCER MICHELS: But some shoppers say it will hurt marine life.
SARAH RATH, Louisiana: I think it's horrible. I think they should stop it. And I don't see how -- how the president doesn't have the -- the authority to stop BP from using this stuff.
SPENCER MICHELS: Why?
SARAH RATH: It's toxic.
SPENCER MICHELS: But how toxic is unclear. Spraying chemical dispersants has slowed considerably since the well was capped, but the longer-term effects are not known.
A product with the catchy name of Corexit is what's being used, made by a company, some of whose executives have ties to BP. On their Web site, the Illinois firm, Nalco, posted this video to show how Corexit works by breaking down the oil.
NARRATOR: Our advanced technologies efficiently and safely disperse oil in the open sea and in freshwater applications, where it can be consumed by microorganisms.
SPENCER MICHELS: The value and the potential danger of dispersants are widely debated. At a Senate hearing last week, Environmental Protection Agency Chief Lisa Jackson explained the dilemma she faced in deciding to allow their use.
LISA JACKSON, Environmental Protection Agency Administrator: Because there are scientific unknowns, we had to make decisions that are a series of trade-offs. And, basically, in common language, it was either nothing or in moderation. And my best judgment was that it should be in moderation.
SPENCER MICHELS: LuAnn White is a toxicologist at Tulane University in New Orleans, and she's convinced that Corexit, used on the surface, is better than leaving the oil to foul beaches. She says that headlines about its toxicity are overblown.
LUANN WHITE, toxicologist, Tulane University & Louisiana Department of Health: There's a lot of misconceptions about the dispersants, because there's been a lot on television, on radio, in the newspapers calling them being highly toxic.
While I wish we were in a situation where we didn't have to use dispersants, they are not the most toxic compound. They're metabolized. They're broken down very well by various organisms. And what that means is that our bodies can handle them.
DAVID VALENTINE, geochemist, University of California, Santa Barbara: You can see that, when I shake that, it's dispersed, that is, the oil is broken down by the Corexit into small little particles.
SPENCER MICHELS: Some scientists like David Valentine at the University of California at Santa Barbara, agree that the dispersant is doing more good than harm, at least on the water's surface.
DAVID VALENTINE: Petroleum is far more toxic than the Corexit. And it's -- it's far more likely to accumulate in seafood and pose a problem. In my opinion, the -- the decision to use Corexit was probably the correct decision. Ultimately, it's keeping oil from getting on the beaches, and it's -- it's minimizing the impact on the shore environment and the economic impact.
SPENCER MICHELS: But he is not totally endorsing the use of dispersants, since never before has Corexit been applied in such volume and at such depth.
The oil and the dispersants don't make it to shore, but they remain in the deep ocean. And he's uneasy about that. He has spent several weeks aboard a research vessel in the Gulf, right near the site of the spill, gathering data about the chemical's effects in the deep sea.
DAVID VALENTINE: It seems that there's been far too much added, at over 750,000 gallons in the subsurface alone, over a million gallons at the sea surface, that those quantities were never envisioned for this -- for this kind of compound. And so, there, I think we have a far different -- different issue and potential problems that may arise, from the sheer quantity applied.
SPENCER MICHELS: What is not known for sure, and yet what scientists disagree about, is the effect of dispersants way under the surface of the water. The temperature there is lower, the pressure is higher. And no one knows exactly what the effect on marine life could be.
That's what marine biologist and environmentalist David Guggenheim wants to know. As he collected samples of water and oil and animal life in and near the Gulf, a flock of spectacular pink birds passed overhead.
DAVID GUGGENHEIM, 1planet1ocean: Those birds, the roseate spoonbills, are a perfect example of what we're worried about with -- because even -- even if we assume that dispersants are not toxic, all of that oil being dispersed throughout the ecosystem is entering the food chain at many different levels.
And those animals eat small mollusks and crustaceans that are in the mud. It's getting into their system. And it accumulates in the tissue over time and can kill em. And the other part of the ecosystem, the real invisible part of the ecosystem, is the deep ocean and the -- the water column, where all of this oil is being dispersed at depth, a mile deep, and can affect a huge geographic area.
SPENCER MICHELS: Filmmaker and oceanographer Jean-Michel Cousteau is convinced the dispersants pose a real danger. He says his own teams have observed how tiny droplets of oil and dispersants linger underwater. They can be ingested by marine life.
We talked with him near his headquarters in California after he returned from the Gulf.
JEAN-MICHEL COUSTEAU, chairman, Ocean Futures Society: Our team took the risk of getting in the water. And it was burning their skin. And they had headache. And they came out.
But we saw that it was everywhere, which means what? It means that, when you have wind, storms, waves, you can put all the booms you want. It goes underneath, and it reaches the critical environmentally sensitive reproduction grounds, which are the marshlands.
For geochemist David Valentine, there is plenty of work ahead, including studying the impact on the oil-eating bacteria that usually help clean up oil spills.
DAVID VALENTINE: We're trying to pull out what the impact of the Corexit might be on the bacteria and their capacity to degrade the oil.
SPENCER MICHELS: And, he says, there more questions than answers.
DAVID VALENTINE: We went into this knowing far less than we should have. Nobody had their eye on the ball. The oil companies didn't. The federal government didn't. Nobody had prepared in any way for this sort of event to occur. Coming out of this, we're going to be slightly more prepared.
SPENCER MICHELS: It could take months or years before scientists know the effect of dispersants. Even BP executives have acknowledged much is still unknown. And fishermen like Ryan Lambert are convinced they will have to cope for years with the aftermath of what's already been sprayed.