Deepwater Horizon Disaster Half a Decade Later: Biodegradation of the Oil Spill

Researchers from UC Santa Barbara and a team from 3 other institutions have analyzed data from the Natural Resource Damage Assessment that identifies the specific rates of biodegradation for 125 major petroleum hydrocarbons or compounds from the Deepwater Horizon oil spill that settled on the ocean floor. In their study published in Proceedings of the National Academy of Sciences, the researchers noted the factors that would influence the environmental impact of the Deepwater Horizon oil spill.

"Now, we can finally take all of this environmental data and begin to predict how long 125 major components of the DWH oil on the deep ocean floor will be there," shared David Valentine, a professor in UCSB's Department of Earth Science and one of the authors of the study. "The way in which we've analyzed all of these different compounds helps answer questions everybody asked right after the 2010 blowout. Yes, we know where a lot of this oil went, and yes, we know what's happening to it. It is slowly being biodegraded, but each compound is acting a bit differently."

The lead author of the study, Sarah Bagby, was a postdoctoral scientist in the Valentine Lab at UCSB when she built a chemical fingerprint of Macondo oil based on its biomarker compounds. She then matched the subset of samples to the corresponding fingerprints and formulated a statistical framework that could analyze each of the 125 individual petroleum hydrocarbons.

"You can make some predictions based on the chemistry," Bagby explained. "The smaller, simpler compounds are going to go away faster. The bigger ones are going to take longer if they go away at all. But superimposed on that are a couple of other trends. The clearest one is that the more heavily contaminated a sample is, the less loss of oil there is. The more lightly contaminated it is, the faster the stuff goes away. That means that the physical context, on a scale of microns to millimeters, makes a huge difference in long-term environmental fate. It's very striking to me that such a small difference can have such a substantial environmental impact."

Samples were classified as lightly, moderately or heavily contaminated and it was discovered that for many compounds, oil degradation had slowed since it had been deposited on the seafloor.

"The data indicates big particles of hydrocarbon that came down to the seafloor are not going away as quickly as smaller ones, which has a variety of implications," Valentine said. "This hadn't previously been observed at this spatial scale or in this sort of environment, so this work is important in understanding the fate of oil that reaches the seafloor."