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August 15, 2011

Some Gulf Spill Hydrocarbons Remain Underwater

Workplace Safety: Soluble hydrocarbons dissolved in ocean, but questions of worker safety, and the fate of less soluble compounds debated

Elizabeth K. Wilson

Aaron L. Sussell/National Institute for Occupational Safety and Health
WHAT'S IN THE AIR? Studies show several toxic hydrocarbons remain dissolved after the Gulf spill. But cleanup worker safety may still be an issue.
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Several new studies of the air and water near the site of the Deepwater Horizon oil spill suggest that a collection of toxic hydrocarbons from the spill remain dissolved in the Gulf of Mexico.

However, researchers have very different takes on the significances of the data. While some tout the lack of release of these compounds into the atmosphere as good news for cleanup workers' health, others worry more about oil compounds that are less water-soluble volatilizing and creating environmental hazards.

The compounds examined in these studies--benzene, toluene, ethylbenzene, and xylene (BTEX)--are toxic compounds found together in petroleum sources. The chemicals, especially benzene, are known to cause a host of health problems, including nausea and bone marrow damage. Scientists frequently use BTEX levels as a way to estimate the environmental and health risks posed by oil spills.

A team led by marine geochemist Christopher Reddy at the Woods Hole Oceanographic Institute, recently analyzed the chemical makeup of samples from a 20-mile-long plume of oil and gas that was heading southwest from the Deepwater wellhead (Proc. Nat. Acad. Sci., DOI: 10.1073/pnas.1101242108). Reddy tells C&EN that since BTEX are relatively soluble in water, it remained below the surface by dissolving into the water column.

San Francisco-based consulting firm ChemRisk looked at BTEX release from a different angle (Environ. Sci. & Tech., DOI: 10.1021/es200963x). Spurred by concerns of cleanup workers' exposure to airborne pollutants from the spill, they analyzed BTEX in the local atmosphere, and found that BTEX levels were well below safety limits required by the U.S. Occupational Safety and Health Administration. They also concluded that the compounds that were detected likely originated predominantly from ship engine exhaust in the area, rather than the oil spill.

Heather Avens, ChemRisk health scientist and lead author of the study, tells C&EN that her group attributes their results to a very low percentage of BTEX in the Gulf spill crude oil, the likely dissolution of large fractions of BTEX in the water column prior to the oil surfacing, and the quick dispersion of volatilized BTEX into the air.

Thomas Ryerson, atmospheric chemist at the National Oceanographic and Atmospheric Administration's Earth System Research Laboratory in Boulder, Colo., and his colleagues also collected atmospheric samples above the spill and recently reported that BTEX levels were only slightly elevated, supporting the idea that the chemicals dissolved in the ocean (Geophys. Res. Lett., DOI: 10.1029/2011GL046726).

Reddy, however, is concerned that these results may engender a false sense of safety for workers and air quality. David Valentine, microbial geochemistry professor at the University of California, Santa Barbara, agrees and points out that other oil compounds, such as naphthalene, have not been well studied at the spill site. These compounds don't readily dissolve in water, he says, but are volatile and could pose a risk to workers at the surface.

"The usual suspects, BTEX, are incarcerated in the deep ocean," Valentine notes. "And now we need to shift our exposure concerns to other suspects."

Chemical & Engineering News
ISSN 0009-2347
Copyright © 2011 American Chemical Society
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