In the wake of the 2010 BP oil spill, cleanup crews dumped some 1.8 million gallons of chemical dispersants into the Gulf of Mexico.
The substances were supposed to assist natural oil-eating bacteria in cleaning up the largest marine oil spill in history by breaking the oil into droplets the microbes could more easily consume.
But the approach backfired, suggests a study published this month in the Proceedings of the National Academy of Sciences.
“The dispersants did a great job in that they got the oil off the surface,” University of Georgia marine scientist Samantha Joye, a co-author of the study, told the Associated Press. “What you see is the dispersants didn’t ramp up biodegradation.”
What’s bothersome, Joye told The Atlantic, is that 24 to 55 percent of the oil spilled from the Deepwater Horizon rig off the Louisiana coast is unaccounted for. She suspects much of it is on the seafloor.
For the study, Joye and her team simulated the Gulf’s conditions in a laboratory. They found that "dispersants can exert a negative effect on microbial hydrocarbon degradation rates."
Oil with no dispersant actually "degraded a heckuva lot faster than the oil with dispersants," she told the AP.
Dispersants work a lot like dish detergent, breaking up oil slicks into lots of small droplets. Gulf responders turned to these chemicals, namely Corexit -- which studies have since shown can be harmful to various types of marine life -- to address the roughly 200 million gallons of oil that spilled from the Deepwater Horizon rig.
The microbes the dispersants were meant to help were the "last (and only) defense" against the ongoing spill, Scientific American noted about a month after the spill.
The major question moving forward: Should dispersants be used to fight future spills?
Doug Helton, coordinator of the National Oceanic and Atmospheric Administration's Office of Response and Restoration Incident Operations, addressed the BP cleanup process on the agency's website this year.
"Once oil is spilled there are no good outcomes and every response technology involves trade-offs," he wrote. For example, he noted, using dispersants to decrease the amount of floating oil puts some organisms and environments at risk, but reduces risk potential for others.
"Until we stop using, storing and transporting oil, we have the risk of spills," he wrote. "The decision to use dispersants or not use dispersants will never be clear cut. Nor will it be done without a lot of discussion of the trade-offs. The many real and heart-felt concerns about potential consequences aren’t dismissed lightly by the responders who have to make tough choices during a spill."
In 2013, despite scientists' claims that dispersants are toxic to marine life, BP CEO Bob Dudley defended their use in the cleanup efforts the company funded.
"In hindsight no one believes that that was the wrong thing and it would have been much worse without the use of it," he said. "I do not believe anybody -- anybody with almost common sense -- would say waves of black oil washing into the marshes and beaches would have been a better thing, under any circumstances."
Joye, however, said a person could argue that in the case of Deepwater Horizon, it would have been better to have left the organisms alone.
"Nobody wants to see oiled birds, turtles and dolphins, but the bottom line is that if you disperse that oil, it's still in the water," she told The Atlantic. "You feel better, but is it improving the situation? My gut instinct is that I would put my faith in the microbial communities to do their job."
Last week, the Gulf of Mexico Research Initiative announced that it will award nearly $38 million to individuals and teams studying the effects of oil, as well as dispersants, on the Gulf of Mexico ecosystem and public health.
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