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Oil-eating microbes in the Gulf of Mexico left behind the most toxic remnants of the Deepwater Horizon spill

Impacts likely to persist for decades

/klj

Oil: Can’t live with it, can’t live without it.

Staff Report

FRISCO — Oil-eating microbes in the Gulf of Mexico may have helped break down some of the pollution from the 2010 Deepwater Horizon disaster, but some of the most toxic constituents of BP’s oil probably remain, most likely at the bottom of the sea.

Two new Florida State University studies in a deep sea oil plume found found that 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 not the polycyclic aromatic hydrocarbons (PAHs), which 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,” said FSU assistant professor Olivia Mason. “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.

Mason’s study isn’t the first to trace the toxic fallout from the Deepwater Horizon disaster. Two years after the spill, University of South Florida researcher James “Rip” Kirby documented PAH remnants in the splash zone of Gulf Coast beaches, showing how easily beach visitors can be exposed to the invisible and poisonous chemicals.

In fact, the weathered tar product from crude oil dispersed with Corexit were found to have PAH concentrations consistently in excess of limits set to identify danger to life and health — IDHL limits, as defined by NOAA’s Office of Response and Restoration.

Other research has shown how exposure to PAHs has played out in commercially and recreationally important fish species in the Gulf, by disrupting the  basic cellular function of heart muscles. Other studies have traced dead corals on the seafloor and sick dolphins in Barataria Bay to the Deepwater Horizon oil.

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