Floating around

US scientists from the University of Georgia said they believe government analysis of the breadth of the Gulf of Mexico oil disaster ignores the fact that much of the spilled oil remains in the sea - in smaller droplets or broken-down forms.

"The idea that 75 percent of the oil is gone and is of no further concern to the environment is just absolutely incorrect," said Charles Hopkinson, one of the five-member team who reexamined the estimates, on a conference call to journalists.

"We just re-analyzed [the government] report and then we went to the next step," Hopkinson said, as quoted by the AFP news agency. "We came up [with the fact that] 70 to 79 percent must still be out there."

Oil deposits in canyon sediment

A separate study conducted by scientists at the University of South Florida showed that oil had turned up in sediments of an underwater canyon in levels that would be toxic to marine organisms.

Oil droplets were found in the sediments of the DeSoto Canyon, which is a spawning ground for fish species on the West Florida Shelf, according to the report.

On August 4, the US government said clean-up efforts and natural degradation had eliminated some 74 percent of the 4.9 million barrels of oil believed to have spilled from BP's ruptured Macondo well into the Gulf's seawater.

"The vast majority of the oil from the BP oil spill has either evaporated or been burned, skimmed, recovered from the wellhead or dispersed," the National Oceanic and Atmospheric Administration wrote.

How fast can oil evaporate?

But Hopkinson said that report was faulty and went on to challenge official estimates of how quickly the oil would dissolve and evaporate.

"One major misconception is that oil that has dissolved into water is gone, and therefore harmless," Hopkinson added. "The oil is still out there, and it will likely take years to completely degrade. We are still far from a complete understanding of what its impacts are."

The government estimated that a significant amount of oil floated to the surface, where it was able to evaporate, but Hopkinson said the gradient of water density at the spill site made it unlikely the oil would have risen far from the well rupture on the seafloor.

In a response to the University of Georgia report, a National Oceanic and Atmospheric Administration (NOAA) spokesman said the government calculation was based "on direct measurements whenever possible and the best available scientific estimates where direct measurements were not possible."

"The government and independent scientists involved in the Oil Budget have been clear that oil and its remnants left in the water represent a potential threat, which is why we continue to rigorously monitor, test and assess short and long-term ramifications," NOAA Communications Director Justin Kenney said in a statement.

Final analysis could take years

The Georgia study did not take into account the 800,000 barrels of oil captured by BP directly at the wellhead, and, unlike the federal analysis, was not subject to peer review.

Ed Overton, a marine scientist at Louisiana University who reviewed the government's estimates and the University of Georgia study were done with different goals in mind.

"The NOAA report was done to help the response and the Georgia report was done to say 'Look there is potential damage and particularly in the offshore area,'" he told AFP.

"The numbers of both reports are not terribly far off," he added. "Both of them are estimates and estimates are a guess. It's a guess by educated folks, but it's still a guess."

Overton said he believed a full assessment of the amount of oil that spewed into the ocean for 87 days and contaminated wetlands, fishing areas and beaches after BP's Deepwater Horizon rig exploded on April 20 could take at least two years.

Author: Sean Sinico (AFP, Reuters)

Editor: Cyrus Farivar