It's now been more than three and a half years since the Deepwater Horizon oil drilling rig leased to BP exploded, causing over 200 million gallons of crude oil to spill into the Gulf of Mexico, the largest offshore oil spill in U.S. history. In terms of the national news cycle, that duration might seem like a lifetime. In terms of an ecosystem as enormous and complex as the Gulf, it's more like a blink of an eye.
"Oil doesn't go away for a very long time," says Dana Wetzel, a biochemist at Mote Marine Laboratory in Florida who's been sampling water, sediments and the tissues of animals living in the Gulf for evidence of persisting oil. "The assumption had been that in a higher temperature environment, bacteria are going to degrade things much more rapidly, and it'll degrade quicker." But in previous research, she's found that even in warm environments, oil residue persists much longer than experts previously thought - in the waters of Tampa Bay, for instance, she found oil a full eight years after a spill.
If you simply dunked a bucket into Gulf waters and tested for petroleum, she notes, you might not find any. But as part of an ongoing project, Mote researchers are employing innovative sampling mechanisms that use pieces of dialysis tubing, which trap oil residue much like a marine organism's tissue does as it filters water. Deployed in metal containers, the pieces tubing gradually filter water over time, collecting any contaminants present.
This oil can persist through a few different mechanisms. After coating sediments, the viscous substance can stick to them for years. There's also evidence that some oil was trapped in the sunken Deepwater Horizon rig itself and continues to slowly bubble upward, accounting for thevisible sheens of oil occasionally seen on the water's surface.