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Experts: Most of Gulf of Mexico oil spill won't be cleaned up

Despite BP's efforts, only a small percentage of the oil from the Gulf of Mexico oil spill will be cleaned up, say experts.

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New method: However, Thursday afternoon officials said they might try an experimental oil-dispersal method that would involve releasing chemicals from under the water. "We were notified that this technique might be more effective in spreading the dispersant at the source on the riser than by using aircraft to spread it on the sea," said Doug Suttles, BP's Chief Operating Officer.

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Leftover oil

As for what happens to the "dispersed oil," that doesn't get skimmed off or burned off or otherwise collected, "We're told it disperses naturally. It eventually breaks up and evaporates. There are different ways, but we're told it just kind of goes away," U.S. Coast Guard's Mendenhall said.

Bacteria can also help degrade most components of oil.

But not all oils are created equally. At first, reports suggested the oil leaking into the Gulf was standard Louisiana crude oil, a type of oil that biodegrades pretty well, Overton said. But sample testing revealed that the leaking oil was a different type, one that contains a very high concentration of components that don't degrade easily, called asphaltenes, according to Overton. He estimates that the concentration of these asphaltic components could be as high as 50 percent in this oil spill, while in other types of crude oil it might be as low as 1 or 2 percent.

"That is bad, bad news, because this oil is going to be very slow to degrade," Overton said today.

Some of the oil sinks to the sea bottom, where it can get buried into an anaerobic zone where there's no oxygen. Oil in these zones stays in a chemically reduced form and doesn't degrade as much, Overton said. But, he added, there's not much life down there to be contaminated.

The oil slick could reach the Mississippi Delta coast as early as Friday, so at least some oil will hit shore. A satellite image of the slick taken Thursday showed it was almost touching the delta.

History as a guide

The 1989 Exxon Valdez spill that fouled over 1,200 miles (1,900 kilometers) of shoreline in Alaska in 1989 has shown that once an oil slick makes landfall and soaks into the beach, it can take decades for the pollution to break down and disappear. About 40 percent of the 10.8 million gallons spilled reached shore in Prince William Sound, according to Short.

"There's still a lot of oil that didn't get cleaned up," from the area around Prince William Sound where the spill occurred, said Daniel Esler, a University Research Associate, based at the Centre for Wildlife Ecology at the Simon Fraser University in British Columbia, Canada.