What happens to oil after an oil spill?
Previously, scientists have focused on one of three fates: it is degraded by microorganisms, it evaporates or it ends up on the beach. But a new study of the 2010 Deepwater Horizon oil spill in the Gulf of Mexico reveals another option. Almost 10 percent of the oil spewed in the disaster was dissolved into the gulf waters by sunlight.
“The amount of oil that was transformed by sunlight into compounds that dissolved in seawater during the 2010 Deepwater Horizon spill rivals that of commonly accepted oil fates, like biodegradation and stranding on shorelines,” study co-author and Woods Hole Oceanographic Institution (WHOI) Marine Chemistry and Geochemistry Department assistant scientist Collin Ward said in a press release.
The research, led by a team of WHOI scientists, was published in Science Advances Wednesday. It establishes that sunlight plays a bigger role in the fate of oil spills than previously thought, ScienceNews reported.
Scientists have known for fifty years that oil can be dissolved in seawater by sunlight through a process called photo-dissolution, the study authors wrote. However, they have never before been able to factor in this process to what happens to oil after a spill, because they didn’t know enough to model the rate at which it occurs.
To answer this question, Ward and his co-author Danielle Haas Freeman took samples of Deepwater Horizon oil and placed it on glass disks, according to ScienceNews. They then subjected the oil to radiation from LEDs that have the same wavelengths as sunlight. Once this was completed, they assessed how much of the oil was dissolved into organic carbon. Based on their experiments, the scientists estimated that three to 17 percent of the Deepwater Horizon oil was dissolved by sunlight, with a best guess of eight percent, according to the study.
The Deepwater Horizon oil spill was the largest ocean spill in U.S. history, spilling almost 210 million gallons of crude and claiming 11 lives, according to the press release. However, the research has implications for other spills as well.
“One of the most fascinating aspects of this finding is that it might impact our understanding of where else the oil is going, and whether the result is good or bad,” Freeman, a Massachusetts Institute of Technology/WHOI Joint Program student, said in the press release. “If this sizable fraction of oil is being transformed by sunlight and is dissolving into seawater, that might mean that less oil is ending up in other places, like sensitive coastal ecosystems. On the other hand, we have to consider the impacts of the compounds on marine organisms before we can decide if the net result is positive or negative.”
The researchers were able to expand their conclusions by creating a series of possible spill scenarios and assessing how different conditions impacted photo-dissolution, The Hill reported. They found that sunlight wavelength made an important difference, with shorter wavelengths able to dissolve more oil than longer ones. The thickness of the oil slick was also a key factor.
“The importance of this process changes dramatically if you are looking at thin versus thick oil slicks,” Freeman said in the press release. “We also found, contrary to popular belief, that this process is relevant in Arctic waters, a particularly important finding given the expected increase in cargo ship traffic and heightened risk of spills in that region. This kind of modeling is critical when forecasting spills and considering the impacts on marine ecosystems.”
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