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Standard Oil-Spill Tests Might Miss Important Class Of Chemicals

Detection: Methods don’t catch about half of total oil compounds in some water and sand samples

by Mark Schrope
January 31, 2013 | A version of this story appeared in Volume 91, Issue 5

Credit: Coast Guard
Crews clean up oil from the Deepwater Horizon spill on a Louisiana beach in 2010.
This is a photo of crews cleaning a Louisiana beach in 2010 after the Deepwater Horizon oil spill.
Credit: Coast Guard
Crews clean up oil from the Deepwater Horizon spill on a Louisiana beach in 2010.

For decades, scientists studying oil spills have relied on the same methods to detect oil compounds. Unfortunately, these techniques miss an entire class of chemicals that have yet to be identified and that could account for about half of the total oil in some samples, according to research presented in January at the Gulf of Mexico Oil Spill & Ecosystem Science Conference, in New Orleans.

Studying these overlooked chemicals may improve scientists’ understanding of oil toxicity and could explain the fate of some of the oil released in the 2010 Deepwater Horizon spill, the researchers say.

Since the 1980s, researchers have relied mostly on gas chromatography to hunt for about 150 different oil chemicals, mainly alkanes and aromatics. Christopher M. Reddy of Woods Hole Oceanographic Institution and colleagues ran an experiment to determine whether the method was missing anything.

First, the scientists measured the amount of all oil-related chemicals in sand samples collected during the Deepwater Horizon spill. Then they ran the samples through a gas chromatograph to measure the amount of the chemicals a spill scientist normally looks for.

Reddy’s team found that the chemicals identified in the standard tests make up only about 50% of the total oil in the samples. Through elemental analysis, the researchers determined that the other substances are oxidized oil compounds. Reddy says that the standard tests don’t catch these molecules because gas chromatography doesn’t readily detect highly oxidized chemicals.

These oxidized compounds could account for some of the “missing” oil from the Deepwater Horizon spill, Reddy says. Other possible explanations include oil buried in ocean bottom sediments or broken down by microbes. Government and academic scientists could explain the fate of only about 75% of the oil released into the Gulf of Mexico.

Reddy’s team published some of their results in 2012 (Environ. Sci. Technol., DOI: 10.1021/es3015138).

Edward B. Overton of Louisiana State University thinks more research is needed before deeming the oxidized compounds significant in terms of environmental impact.



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