Chemical dispersants dropped from a plane following the BP oil spill in 2010 removed oil from the Gulf of Mexico’s surface but did not fully degrade it – and even interfered with oil-munching microbes’ ability to remove the slick.
These were the findings of a new study conducted by marine scientists from the University of Georgia, who lab-simulated the conditions of the Deepwater Horizon oil spill that released over 172 million gallons of oil in the gulf after the 2010 spill. After the incident, about 1.8 million gallons of Corexit 9500 were employed as a “first line of defense” to break down oil on the surface and deep waters.
Examining microbial oil degradation in the Deepwater plume and writing in the Proceedings of the National Academy of Sciences, the team found that chemical dispersants significantly changed the Gulf's deep water microbial composition through supporting the growth of Colwellia or dispersant-degrading microorganisms.
After testing more than 50,000 bacteria, the research also discovered that the dispersants did not assist in the growth of marinobacter – fat little oil-munching bacteria – or increased the speed at which they consumed the oil. Instead the chemicals appeared to inhibit growth, suggesting that the microorganisms could likely have been better off by themselves.
Lead author and marine sciences professor Samantha Joye said that results echoed the effectiveness of marinobacters in degrading oil, but that the process was more efficient without the chemical agents.
According to co-author Sara Kleindienst of Germany’s University of Tübingen, marinobacter were not abundant in samples of deep-water plume during the spill, probably as a result of applying dispersants. She cited two possibilities: the natural hydrocarbon-eating bacteria could be outcompeted by Colwellia or affected directly by dispersant-derived compounds.
The researchers urged a further study of these chemical aides and their effects not only on the discharge cleanup but also the indigenous bacterial environment.
"The fact that dispersants drove distinct microbial community shifts that impacted oil degradation efficiently came as a big surprise," Joye said, adding it is crucial to quantify elements influencing how these chemical products work.
In July this year, BP agreed to pay $18.7 billion over 18 years as a settlement for all government claims arising from the massive oil spill, which killed 11 workers and caused economic and environmental damaged. At its heels after the breach of the Clean Water Act were four states as well as over 400 local governments.
