We’re only a couple of months shy of the one-year anniversary of the Gulf oil spill, but there’s still a great deal of uncertainty over just what happened—and what might be left over. As I’ve written before, recent studies seem to jibe with the government’s earlier reports suggesting that much of the oil in the Gulf has either evaporated or been broken down by bacteria. (Other scientists, however, still have their doubts.) But hydrocarbons weren’t the only thing that spilled into the Gulf when BP’s Deepwater Horizon rig exploded on April 20 last year. The joint industry/government response team also injected roughly 800,000 gallons of dispersant in the deep water at the site of the leak—something that had never been done in an oil spill response before. There was no shortage of environmental worries about the chemical dispersants when they were used, although the Environmental Protection Agency—after the fact—ruled the chemicals safe. Even at best, regulators and scientists viewed dispersant use as a tradeoff—their usefulness as cleaning agents would balance out any potentially harmful side effects. But we couldn’t make that judgement until researchers could be sure how much damage, if any, the dispersants might have caused.
It turns out the case still isn’t closed. According to a forthcoming study in the journal Environmental Science & Technology, the dispersants used to help clean up the oil spill did not break down as quickly as scientists had expected—meaning that the chemicals are likely still floating in the deep Gulf, at detectable levels. A team led by Woods Hole Oceanographic Institution chemist Elizabeth B. Kujawinski found that one of the key ingredients in dispersants—the chemical dioctyl sodium sulfosuccinate (DOSS) was present in May and June in parts per million concentrations in the plumes of oil and natural gas that spread from the leak. Later on DOSS was detected at much lower concentrations of parts-per-billion in September. Moreover, using chromatographic techniques, the team found no evidence that any biodegradation of the dispersant occurred—the reduction in the concentration was due to simple dilution. As David Valentine, a co-author at the University of California-Santa Barbara, said in a statement:
The results indicate that an important component of the chemical dispersant injected into the oil in the deep ocean remained there, and resisted rapid biodegradation. This knowledge will ultimately help us to understand the efficacy of the dispersant application, as well as the biological effects.’
But the study doesn’t answer the big question: is this level of dispersant actually toxic to sea life? It’s hard to know, though Kujawinski has noted that dispersants are considered toxic until they’ve reached levels of concentration 1,000 times greater than what was observed in the study. But this is all new territory, and as the EPA’s scramble to actually tests the chemical dispersants for toxicity even as they were being deployed shows, we don’t really know that much about what they might do in the ocean—especially in the unprecedented amounts that were deployed in the spill response. Nor, for that matter, do we even know how effective all those chemicals really were. That will take more study—and since it’s almost certain this won’t be the last time we spill oil into the Gulf, or another body of water, it would be nice to get ahead of the curve.