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Where Did BP's Oil Go?

So what happened to the millions of barrels of oil that leaked out of BP's Macondo well? Where did it all go? Here's a chart from a new study by the National Oceanic and Atmospheric Administration (click to enlarge):

Rough summary: About one-quarter of the oil is still bobbing on the sea surface or washed ashore. Another quarter has been dispersed into microscopic droplets, either by artificial chemicals or natural processes. And another quarter has been "dissolved." All told, just 25 percent has been physically removed from the Gulf ecosystem. The rest is still lurking... somewhere. But what sorts of harm is that lingering oil doing? As the NOAA notes, answering that question will take time and a lot more research.

Consider the "dissolved" oil. This crude didn't just vanish entirely—it's still mixed in with the water. A number of marine scientists have pointed out that dissolved oil can still poison the small organisms that underpin the Gulf's food chain. As The New York Times reported last week, "The effect on sea life of the large amounts of oil that dissolved below the surface is still a mystery. Two preliminary government reports on that issue have found concentrations of toxic compounds in the deep sea to be low, but the reports left many questions, especially regarding an apparent decline in oxygen levels in the water."

Then there's the dispersed oil. The crude that's been naturally dispersed will biodegrade more rapidly, thanks to bacteria that thrive in the warm Gulf waters. But then there are the chemical dispersants that BP used to break up the oil and send it into deeper waters (rather than have it wash up onshore). These chemicals had never been used on such a broad scale before, and no one is quite sure what effect they'll have on the ocean ecosystem.

On Tuesday, the EPA announced the results of a second round of tests on the chemical dispersants used by BP, and found that a dispersant/oil mixture was no more toxic than oil alone to silverside fish and mysid fish. That still leaves a lot of questions, however. At a Senate hearing on dispersants today, Lousiana State University environmental scientist Edward Overton pointed out that these tests "have no relevance at all to the deep sea." What's more, the effects of dispersants on other organisms may not be visible for years—say, if sea turtles feed on the toxins and then their hatchlings die.

All told, there were good reasons to disperse the oil and prevent it from reaching the salt marshes on the Gulf shore—where the crude was certain to cause serious long-term damage. But as NRDC's Lisa Suatoni notes, it's still too early to conclude that dispersant use was ultimately the safer option. We still don't know where all the dispersed oil went, or what organisms it encountered, or how it's affecting the Gulf's food web. BP may have capped its leaking well, but we're still very far from knowing just how bad the spill really was.

P.S. Kate Sheppard makes a good framing point. It may be the case that only one-quarter of the oil is left in big, thick, visible doses, but that's still more than 50 million gallons of oil—about five times the size of the Exxon Valdez spill.