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Standard Oil Spill Tests Might Miss Important Class Of Chemicals

Oil Spills: Detection methods don’t catch oxidized molecules that could account for about half of total oil in some water and sand samples

by Mark Schrope
January 30, 2013

Washed Up
Credit: Mark Schrope
Oil from the Deepwater Horizon spill floats in shallow water at a beach in Louisiana in 2010.
Photograph of oil from Deepwater Horizon spill in shallow water at a Louisiana beach.
Credit: Mark Schrope
Oil from the Deepwater Horizon spill floats in shallow water at a beach in Louisiana in 2010.

For decades, scientists studying oil spills have relied on the same analytical methods when tracking the movement of oil and assessing a spill’s environmental impact. But these techniques miss an entire class of compounds that could account for about half of the total oil in some samples, according to research presented last week at the Gulf of Mexico Oil Spill & Ecosystem Science Conference, in New Orleans. Detecting these chemicals may improve scientists’ understanding of oil toxicity and could explain the fate of some of the oil released in the 2010 Deepwater Horizon accident and other spills, the researchers say.

Christopher M. Reddy, of the Woods Hole Oceanographic Institution, had long wondered whether the standard suite of oil detection methods caught all the important compounds, even ones produced as the oil degrades. Since the 1980s, researchers have relied mostly on gas chromatography to measure oil levels in samples from spill sites by hunting for about 150 different chemicals, mainly alkanes and aromatics.

To determine if other types of compounds went undetected by these standard methods, Reddy’s team ran two tests on beach sand samples collected during the Deepwater Horizon spill. In the first one, they used an organic solvent to extract all of the oil compounds from the sand. The researchers then weighed the resulting material to determine the amount of total oil-related compounds. In the second experiment, they ran the samples through a gas chromatograph to measure the amount of the chemicals a spill scientist normally looks for.

The Woods Hole team found that the chemicals targeted in the standard tests made up only about 50% of the total oil in the samples. “I just couldn’t believe it,” Reddy says. He asked his colleagues to run the experiments multiple times before accepting the results.

Through elemental analysis, the researchers determined that the previously undetected substances were oxidized oil compounds, possibly produced as the oil degraded in sunlight. Reddy says that the standard tests didn’t catch these molecules, because gas chromatography doesn’t readily detect highly oxidized chemicals. The team published some of their results in 2012 (Environ. Sci. Technol., DOI: 10.1021/es3015138).

Reddy says overlooking these chemicals could hinder spill research in several ways, including thwarting scientists’ attempts to account for what happens to oil after a spill. After the Deepwater Horizon spill, government and academic groups could only explain the fate of about 75% of the oil released into the Gulf of Mexico. The oxidized compounds could be a portion of this “missing” oil, Reddy says.

Also, Reddy points out that other researchers have reported that compounds not normally monitored by the standard tests may harm marine organisms. For example, one study linked unidentified oil chemicals to a spike in fish embryo deaths after a 2007 spill in San Francisco Bay (Proc. Natl. Acad. Sci. U.S.A., DOI: 10.1073/pnas.1108884109).

The team is now working to identify specific chemicals missed by the standard tests, assess the compounds’ toxicity, and determine how they are formed during a spill.

Edward B. Overton, a professor emeritus at Louisiana State University, who analyze. oil samples for the National Oceanic and Atmospheric Administration, is happy the researchers are looking into compounds overlooked by the standard methods. But he thinks more research is needed before deeming the compounds significant. In particular, the team should determine the effects the compounds have on marine organisms, he says.


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