Plumes of Oil Below Surface Raise New Concerns

The government and university researchers confirmed Tuesday that plumes of dispersed oil were spreading far below the ocean surface from the leaking well in the Gulf of Mexico, raising fresh concern about the potential impact of the spill on sea life.

The tests, the first detailed chemical analyses of water from the deep sea, show that some of the most toxic components of the oil are not necessarily rising to the surface where they can evaporate, as would be expected in a shallow oil leak. Instead, they are drifting through deep water in plumes or layers that stretch as far as 50 miles from the leaking well.

As a rule, the toxic compounds are present at exceedingly low concentrations, the tests found, as would be expected given that they are being diluted in an immense volume of seawater.

“It’s pretty clear that the oil that has been released is becoming more and more dilute,” Jane Lubchenco, head of the National Oceanic and Atmospheric Administration, said in an interview. “That does not mean it’s unimportant — far from it. The total amount of oil out there is likely very large, and we have yet to understand the full impact of all that hydrocarbon on the gulf ecosystem.”

BP’s chief operating officer, Doug Suttles, continued to insist Wednesday morning on the “Today” show on NBC that no underwater oil plumes in “large concentrations” have been detected from the spill, saying that it “may be down to how you define what a plume is here.”

But scientists outside the government noted that the plumes appeared to be so large that organisms might be bathed in them for extended periods, possibly long enough to kill eggs or embryos. They said this possibility added greater urgency to the effort to figure out exactly how sea life was being affected, work that remains in its infancy six weeks after the Deepwater Horizon oil rig exploded.

“I’m glad to see the levels are low,” said Carys L. Mitchelmore, an aquatic toxicologist at the University of Maryland who was not involved in the research. “But we’re talking about a huge Gulf of Mexico here. I want to see evidence that this is one of the main plumes and there’s not something way more concentrated somewhere else.”

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