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BP Gulf spill: where has all the oil gone?

By Channel 4 News

Updated on 29 July 2010

Virtually all of the oil spilled by the BP oil leak that was floating on the surface of the Gulf of Mexico has vanished, but is that a good thing? Science correspondent Tom Clarke explains the fears that the oil has been dispersed into such small quantities it is now in the food chain.

An oil sheen covers the surface of Bay Jimmy near Port Sulpher, Louisiana from the BP oil spill (Reuters)

Experts in the United States say millions of barrels from the Gulf oil spill remains unaccounted for in official statistics. While much of it may have evaporated and some has been eaten by oil-munching bacteria, a large amount could still lurk in vast plumes beneath the surface, with potentially long-term consequences some scientists warn.

BP capped the well two weeks ago, and almost immediately oil stopped appearing on the surface of the Gulf of Mexico (see animation right).

In a press briefing last night US coastguard boss Admiral Thad Allen said that around 1.2 million barrels of oil were skimmed off and land filled, or burned on the sea surface. But that leaves a very rough estimate of 4 million barrels of oil still missing in the Gulf.

It's thought much of it could have been naturally broken down by a resilient ocean.

"There is evaporation and then there is natural weathering of the oil. And this varies with the type of oil and where you are at in the world. We happen to be in an area where there are high temperatures and optimal conditions environmentally," Allen said.

It is estimated up to 40 per cent of the oil may have evaporated in the heat. Also, the Gulf – an area of naturally occurring oil seeps – is rich in oil-eating microbes that, given sufficient oxygen, can break down oil very quickly into carbon dioxide and water.

But the latest oil measurements only take into account surface oil. BP used 800,000 gallons of dispersant on oil leaving the well a mile beneath the sea.

It is likely millions of gallons of oil still remain dispersed in fine droplets in the water column. Some of these plumes have been detected and low levels of oxygen associated with them suggest bacteria are getting to work on the oil.

But it is not certain how conducive the environment deep in the ocean will be to breaking down the toxic components of crude oil?

"There clearly remain an awful lot of oil products that are unknown at the moment," George Crozier, Director of the Dauphin Island Sea Lab in Alabama, told Channel 4 News.

He worries that the low oxygen levels in the deep waters could mean toxic compounds in the oil will have time to accumulate in the gulf ecosystem – eventually working their way into the food chain.

But Crozier, like many Gulf coast scientists accepts that the Gulf is well suited to dealing with the oil: "This is not the end of the Gulf of Mexico, the Gulf has the capacity to detox this exposure. But the question is, is it going to take days, weeks, months or years," he says.

BP announced today that they want to start pumping mud down into the capped well-head as early as Sunday – a manoeuvre called "static kill." They claim this could plug the well as early as Monday or Tuesday.

However, it's not expected the well to be securely sealed until relief wells are completed in the first week or two of August.

 

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