Washington’s Blog 
Aug 22, 2010
As you might have heard, scientists are finding gigantic under oil plumes from the BP spill, including one that is more than 22 miles long, more than a mile wide and 650 feet deep .
On Thursday, Dr. Ian MacDonald and and Dr. Lisa Suatoni testified to a Congressional subcommittee that the oil will stay toxic, and will not degrade much further, for decades. MacDonald  is an expert in deep-ocean extreme communities including natural hydrocarbon seeps, gas hydrates, and mud volcano systems, a former long-time NOAA scientist, and a professor of Biological Oceanography at Florida State University. Suatoni  has a PhD in Ecology and Evolutionary Biology from Yale, and is Senior Scientist at the Natural Resources Defense Council’s Oceans Program.
Dr. MacDonald told Congress that the oil has already degraded, emulsified and evaporated about as much as its going to, and it is going to very resistant for further biodegradation. The oil will be in the environment for a long-time, he said, and the imprint of the BP discharge will be detectable “for the rest of my life” (he’s 58, and the average lifespan for American men is about 76 ; so that’s some 18 years).
Dr. Suatoni told Congress that oil which goes into low-oxygen zones will remain in a full toxic form for decades.
Why isn’t the oil degrading faster?
As National Georgraphic noted  Thursday:
The oil plume’s stability is “a little unexpected,” study leader Richard Camilli, of WHOI’s Applied Ocean Physics and Engineering Department, said at a Thursday press briefing in Washington, D.C.
“We don’t have any clear indication as to why it set up at that depth.”
It’s unclear why the Gulf’s microbes aren’t eating the oil plume, but the organisms are infamous for being unpredictable, said study co-author Christopher Reddy, a marine chemist at WHOI.
Further studies are needed to figure out why the plume isn’t degrading, Reddy said during the press briefing ….
Indeed, one of the world’s leading experts on oil-eating bacteria told me yesterday  that the main oil-eaters aren’t even present in the underwater plumes he sampled.