Pelicans covered in oil from the Deepwater Horizon spill arguably one of the greatest environmental disasters in history "Gulf-Oiled-Pelicans-June-3-2010" by International Bird Rescue Research Center - originally posted to Flickr as Gulf-Oiled-Pelicans-June-3-2010. Licensed under Creative Commons Attribution 2.0 via Wikimedia Commons

Pelicans covered in oil from the Deepwater Horizon spill, arguably one of the greatest environmental disasters in history.

Researcher: Bacteria Ate Some Gulf Spill Toxins, but Worst Remain

Half the sediment samples taken near the site of the Deepwater Horizon wellhead in the Gulf of Mexico contain levels of polycyclic aromatic hydrocarbons that exceed EPA’s water-quality benchmarks for aquatic life.

A Florida State University researcher found that bacteria in the Gulf of Mexico consumed many of the toxic components of the oil released during the Deepwater Horizon spill in the months after the spill, but not the most toxic contaminants.

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. However, her research also shows 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  ocean floor.

The most toxic contaminants, polycyclic aromatic hydrocarbons or 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 not been accounted for, and 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 EPA’s water-quality benchmarks for aquatic life.

Mason’s first paper, which specifically examined how the bacteria ate – or didn’t eat – toxins in the sediments, appeared in the International Society for Microbial Ecology Journal. The second, which focused on how and why the bacteria Colwellia flourished in the water column in the deep-sea plume, was published in Frontiers in Microbiology.

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