Gulf oil spill researcher: Bacteria ate some toxins, but worst remain, research finds

In two new studies conducted in a deep sea plume, Assistant Professor Olivia Mason found a species of bacteria called Colwellia likely consumed gaseous hydrocarbons and perhaps benzene, toluene, ethylbenzene and xylene compounds that were released as part of the oil spill.

But, her research also showed that bacteria did not consume the most toxic parts of the oil spill in the water column plume or in the oil that settled on the seafloor.

The most toxic contaminants are called polycyclic aromatic hydrocarbons or PAHs. PAHs are a group of semi-volatile organic compounds that are present in crude oil and can cause long-term health problems such as cancer.

"Those PAHs could persist for a long time, particularly if they are buried in the ocean floor where lack of oxygen would slow PAH degradation by microorganisms," Mason said. "They're going to persist in the environment and have deleterious effects on whatever is living in the sediment."

When the Deepwater Horizon spill occurred, more than 4 million barrels of oil spilled into the Gulf of Mexico. Some of that oil has never been accounted for, and thus has unknown environmental and health consequences for the region.

Mason and colleagues investigated the oil deposits on 64 sediment samples in different areas around the oil wellhead.

To understand the functional capacity of the microorganisms to degrade oil, microbial DNA was sequenced in 14 of those samples. Of those 14, seven of the samples were so contaminated with PAHs that they exceeded the U.S. Environmental Protection Agency's water quality benchmarks for aquatic life.