Dispersants fail: Half the spilled BP oil may be on Gulf floor

ATHENS, Ga., Nov. 10 (UPI) --

New research suggests a chemical dispersant used in the wake of the BP oil spill failed to help, and may have actually hindered, the cleanup.

A study led by researchers at the University of Georgia showed a chemical concoction thought to encourage the oil's breakdown, in fact, hampers the ability of microorganisms to naturally degrade the hydrocarbons.

Scientists recreated the conditions of the Gulf of Mexico oil spill in the lab, closely monitoring the effects of a chemical dispersant called Corexit 9500 on oil slicks and the microbes that feed on them.

The dispersant didn't depress the presence of all microbes. Corexit 9500 dramatically boosted the presence of a family of microbes called colwellia. Colwellia's proliferation, however, came at the expense of a group of sausage-shaped bacteria called marinobacters. Marinobacters are better oil-eaters.

The experiments showed that a diverse community of microbes actually break down the oil much faster in the absence of Corexit 9500.

Researchers published their findings in the journal PNAS.

The fact that dispersants drove distinct microbial community shifts that impacted oil degradation efficiently came as a big surprise, lead study author Samantha Joye, a science professor at Georgia, said in a press release. It is critical to quantify the factors that influence the efficiency of oil biodegradation in the environment, and that includes dispersants.

Cleanup officials failed to monitor the biological or chemical effects of the dispersants. But visual observations suggested the oil slicks were removed from the surface. The new research suggests much of that oil may have simply sunk.

Joye says the dispersants worked to remove oil from the surface, but not at encouraging microbial oil digestion. And deep water samples suggest microbial conditions beneath the surface weren't any better.

During the spill, Marinobacter were not abundant in deep-water plume samples, possibly as a consequence of dispersant applications, said study co-author Sara Kleindienst, a researcher at the University of Tubingen in Germany. Whether natural hydrocarbon degraders were outcompeted by dispersant degraders or whether they were directly affected by dispersant-derived compounds needs to be resolved in future studies.

The findings mean much of the oil may have simply sunk to the bottom, never degraded.