Chemical dispersants added to spilled oil from the 2010 Deepwater Horizon disaster in the Gulf of Mexico (pictured) may have made little difference to the rates at which microbes broke down the oil.

Credit: Daniel Beltrá/Greenpeace

The dispersants broke up the oil into smaller droplets to help sea-dwelling microbes to degrade it further. To study the chemicals' effect on the microbes, Samantha Joye at the University of Georgia in Athens and her colleagues created bottled mixtures of sea water, oil and dispersants that simulated environmental conditions during the spill.

Mixtures of oil and sea water were dominated by Marinobacter species, which can degrade a wide range of hydrocarbons. But these populations dropped when dispersant was added, whereas Colwellia, which degrades dispersants, increased in abundance. Adding dispersants did not seem to change the rate at which hydrocarbons were broken down in the bottled samples.

Proc. Natl Acad. Sci. USA http://doi.org/89f (2015)