WASHINGTON - Many scientists say they're skeptical of a widely publicized government report Wednesday that concludes much of the oil that gushed from BP's leaking well is gone and poses little threat to the Gulf of Mexico.
According to the National Oceanic and Atmospheric Administration, the "vast majority" of the 4.9 million barrels released into the Gulf has either evaporated "or been burned, skimmed, and recovered from the wellhead, or dispersed."
"I'm suspect if that's accurate or not," said Ronald Kendall, the director of the Institute of Environmental and Human Health at Texas Tech University and one of the scientists who testified Wednesday at a congressional hearing about the need for more research into the composition and use of chemical dispersants to break up the oil in the Gulf.
"It's an estimate and I'd like to say that even if it's true, there are still 50 to 60 million gallons that are still out there," he said. "It's too early to draw the conclusion that the coast is clear, but there are species there that will tell us.''
The White House used the report to boost public confidence that the accident at BP's drilling site, which killed 11 workers, fouled the Gulf, killed wildlife and disrupted the regional economies from Texas to Florida, is now behind the nation.
Many scientists, however, questioned both the rosy White House assessment and the administration's motives, timing and record of estimating how much oil was flowing from the well.
The report says that less than half of the oil remains in the environment. About 26 percent of it remains as surface sheen or tarballs, or other forms of oil. About 16 percent was dispersed naturally, and another 8 percent was dispersed by the chemicals BP pumped onto the surface of the Gulf and deep underwater at the source of the leak.
Jane Lubchenco, NOAA administrator, said at a White House press conference that "Much of the dispersed oil is in the process of relatively rapid degradation."
Obama Press Secretary Robert Gibbs, the president's energy and climate change adviser, Carol Browner; and Thad Allen, who as the national incident commander directed the BP cleanup, joined Lubchenco at the White House briefing.
President Barack Obama, addressing the AFL-CIO on jobs, expressed optimism that "the long battle to stop the leak and contain the oil is finally close to coming to an end." Early Wednesday, BP reported that it had stopped the leak by pumping heavy drilling mud into the well shaft.
The scientists and other experts who challenged the government's conclusions warned that painting too rosy a picture could hamper the environmental monitoring and cleanup work that remains to be done in the Gulf.
Marine conservationist Rick Steiner, a retired University of Alaska scientist, said: "Let's look at this another way: that there's some 50 percent of the oil left. It's still there in the environment."
The government report also fails to account for the effect of vast, underwater plumes of microscopic droplets of oil that remain unmeasured, scientists said, and it downplays the potential long-term effects of the release of as much as 4.1 million barrels of oil in the Gulf of Mexico. Some 800,000 barrels were captured at the wellhead.
The remaining 50 percent in the water is the equivalent of almost eight Exxon Valdez oil spills, until now the country's benchmark environmental disaster.
"Now what we're hearing is they don't think the damage will be as bad as they initially thought," Steiner said. "We have to remember that the same thing was said after the Exxon Valdez. But much of the damage didn't become apparent until the second or third year."
Scientists also questioned the report's methodology.
"There is a lot of uncertainty in these figures," said James H. Cowan, Jr., a professor in the Department of Oceanography and Coastal Sciences at Louisiana State University,
For example, the report doesn't explain how its authors decided what was naturally dispersed oil and what was chemically dispersed oil. They gave no details of how they estimated the evaporation rate of oil - something that's difficult to do over large areas of seawater because of the effects of weather and other factors, Cowan said.
In the face of the criticism, administration officials bristled at questions about their findings.
Lubchenco said the data was "the best direct measurements or estimates that we have at the moment" and that if new information surfaces, the government would adjust its findings "as is always the case in science." Browner said, "There could be some change" but said the likelihood of any large-scale revision was "very, very small."
Gibbs rejected the notion that the timing and framing of the report were meant to gloss over questions or to reassure Americans. "This isn't a reassurance document," he protested. "It's a compendium of where the oil is." Alluding to President George Bush's premature declaration of victory in Iraq, Gibbs said "there's no 'Mission Accomplished' banner" and that "we're not leaving the area, and more importantly we're not leaving behind any commitment to clean up the Gulf Coast."
Nonetheless, Lubchenco made clear she and other scientists have lingering concerns about safety and environmental implications.
"I think the common view of most of the scientists inside and outside government is that the effects of the spill will likely linger for decades," she said.
The oil already has killed creatures in the water, possibly including the eggs and young of Atlantic blue fin tuna, a giant fish that has been heavily overfished.
The oil that remains in small droplets also could be toxic to small creatures. The oil beneath the surface is "very dilute" and "disappearing very quickly," Lubchenco said, "but dilute and out of sight doesn't necessarily mean benign."
Both the oil that remains and the chemical dispersants used to break them up can cause ecological damage, said Greg Butcher, a scientist who directs bird conservation at the National Audubon Society.
A key concern is that the oil and dispersants would kill small fish and shrimp and other creatures at the bottom of the food chain. In that case, "big fish and birds are all likely to go hungry," he said.
Rescuers continue to find oiled birds, Butcher said. There haven't been the huge numbers of bird deaths as there were in the Exxon Valdez spill, "but that doesn't mean we're home free," he said.
Birds are beginning to move from breeding grounds to other areas as the breeding season ends and could hit oily water as they move. Shore birds are starting to migrate now, and migratory ducks will start to move through the area in September, he said.
One of the scientists, who also testified before Congress on Wednesday and contributed to the government report, said he wasn't surprised by the findings. Edward Overton, an emeritus professor of environmental sciences at Louisiana State, acknowledged that oil in deep water is unlikely to degrade as quickly because of colder water temperatures and lower oxygen levels.
However, he also said that organisms living in deep water are acclimated to living in some amount of crude oil - an amount of oil equal to two Exxon Valdez oil spills seeps naturally out of the sea bottom every year, he said.
"I think what is left is degrading rapidly,'' Overton said. "I keep asking everyone I see, 'You seen oil?' And the answer is 'nothing.'"
Lesley Clark also contributed.