After the 2010Deepwater Horizon spill released millions of barrels of oil into the Gulf of Mexico, disaster response officials resorted to a desperate measure. They sent aircraft to spray chemical dispersants onto the spreading oil. The idea was to break up the spill into smaller droplets, which could be more easily consumed by oil-eating microbes in the Gulf water.
At the time, dispersants seemed like an ingenious strategy for utilizing what Scientific American called "the last (and only) defense" against the Gulf's environmental disaster. But in retrospect, it may not have been such a smart move.
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A newly published study led by University of Georgia scientists, in which they simulated the Gulf's conditions in the laboratory, has found that in some cases the dispersants actually can inhibit the microorganisms that naturally degrade oil spills.
The study found that the dispersants didn't help assist the growth of natural hydrocarbon-degrading Marinobacter, or increase the rate at which the microorganisms consumed the oil, either in deepwater or surface environments. Instead, it actually seemed to inhibit growth. The microorganism fared better in water that didn't contain the chemicals.
The study, published in Proceedings of the National Academy of Sciences, concluded that the chemicals, which were released in deep water as well as on the surface of the Gulf, didn't cause the microbes to biodegrade the oil, as intended. Instead, as the researchers wrote, "Direct measurement of alkane and aromatic hydrocarbon oxidation rates revealed either suppression or no stimulation of oil biodegradation in the presence of dispersants."
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If the laboratory results hold true in the real world, "dispersants can exert a negative effect on microbial hydrocarbon degradation rates," the researchers concluded.
The study is the latest bad news about dispersants. A study published in 2012 in PLOS ONE found that they may have harmed the Gulf's population of zooplankton, depriving fish of a vital food source. Another study that appeared in the same journal in April 2015 concluded that a dispersant used in the Gulf disaster was linked to gill damage in fish and lung damage in humans.
On NOAA's website, Dave Shelton, coordinator of the agency's office of response and restoration incident operations, conceded that the use of dispersants is problematic. "Once oil is spilled there are no good outcomes and every response technology involves trade-offs," Shelton wrote in a recently revised essay.