A detailed analysis of air quality samples taken in the Gulf of Mexico in the weeks and months following the Deepwater Horizon oil spill last year finds no evidence that off-shore cleanup workers there faced health risks from exposure to certain volatile organic chemicals, including benzene.

The independent study, undertaken by ChemRisk, a leading scientific consulting firm, found that exposure to airborne benzene, toluene, ethylbenzene and xylene (BTEX) fell well below the Permissible Exposure Limits (PELs) established by the U.S. Occupational Safety and Health Administration (OSHA).

The report comes after months of debate and speculation about possible health risks to cleanup workers. The chemical compounds that were the subject of the study occur naturally in crude oil at very low percentages. Chronic exposures to sufficiently elevated levels of benzene may cause bone marrow damage and lead to an increased risk for developing acute myeloid leukemia.

In conducting the study, ChemRisk analyzed the BTEX measurements from the nearly 5,000 personal air samples taken by BP during the six months following the spill, including vast numbers of samples taken both before and after the well was capped on July 15, 2010. The report found that the measurements for each of the four BTEX chemicals were 32-fold, 510-fold, 360-fold and 77-fold lower, respectively, than the PELs established by OSHA. The report also found no significant variations in the levels of these compounds before versus after the well was capped, leading to the conclusion that the predominant source of the measured BETX did not appear to be from the oil, but rather was likely from other sources such as  the engines of watercraft assisting in the cleanup.

In all, ChemRisk's analysis noted that in 98 percent of measurements taken by BP of breathing zone air samples for offshore workers before the well was capped and in 99 percent of the measurements taken after the well was capped, no detectible levels of benzene were found.  In addition to ChemRisk's analysis of BP's measurements, similar studies conducted by OSHA and the U.S. Department of the Interior have also shown similarly high non-detect rates.

"This report, which examines the largest body of statistical evidence available, finds that the levels of benzene and other BTEX chemicals were well below the thresholds the federal government has established for determining potential health hazards," said Dennis Paustenbach, president of ChemRisk and a co-author of the study. "The findings of this report are also consistent with the results of smaller sample-group studies conducted by the federal government, and should lay to rest any suggestion that off-shore cleanup workers faced any increased risk of illness from benzene while working to control the effects of the spill."

The report is being published today in Environmental Science and Technology, a leading peer-reviewed scientific journal. A link to the report can be found here: