CORVALLIS, Ore. - Although the flow of oil from the Deepwater Horizon spill was halted in mid-July, researchers continue to find elevated concentrations of polycyclic aromatic hydrocarbons, or PAHs, in some areas of the Gulf of Mexico.

Some of these chemicals are known carcinogens that pose a range of risks to human health.

Oregon State University researchers began testing for the contaminant May 9, and preliminary results, which have not yet been fully analyzed, suggest that the level of PAHs in the water off the coast of Louisiana experienced a 40-fold increase from May to June. The July data was lost when the device the OSU team uses for water sampling disappeared.

However, an initial analysis of the August data continues to show abnormally high levels of PAHs, similar to the 40-fold increase discovered earlier in the summer, said Kim Anderson, a professor of environmental and molecular toxicology in OSU's College of Agricultural Sciences.

"We were able to deploy sampling devices prior to the contamination of the areas we are observing," said Anderson, "In doing so we were able to establish a baseline, and to then monitor concentrations of the PAHs from there."

PAHs can be produced in the environment by both human and natural events. Sources of PAHs can include: living organisms like vegetation; geological processes, including seeps, coal outcrops, crude oil spills and the release of fossil fuels; and the high-temperature combustion of organic materials, as in the case of forest fires, car exhaust and the burning of wood stoves.

In some cases, they are a significant toxicological health concern. Of the more than 100 chemicals that make up the class, a fraction of them can result in harmful health effects after exposure.

"There are a range of health effects associated with PAHs," said Anderson. "They are toxic by several different modes of action. We're now using a technique that looks at the fraction of PAHs that are bioavailable - that have the potential to move into the food chain."

Anderson and her team are collecting samples from both the water and air along about 400 miles of the Gulf coastline. They are using passive sampling devices that Anderson originally developed as part of OSU's Superfund Research Program funded by the National Institute of Environmental Health Sciences (NIEHS).

According to NIEHS, these devices will provide important information about how chemical dispersants used to mitigate the oil spill affect the bioavailability and toxicity of PAHs.

The research is being funded with emergency discretionary grant funding from OSU's Environmental Health Sciences Center, which is supported by the NIEHS. Anderson plans to continue sampling for PAHs - and their oxygen-containing derivatives, OPAHs - at least through the end of the year.

OPAHs are of great concern along the Gulf Coast because they are more mobile, persistent in the environment and likely bioavailable. They form when PAHs react to sunlight and degrade in the atmosphere. Recently, OPAHs have been shown to form and accumulate after the biological remediation of PAH contaminated soils, and it is hypothesized that the same will be true in water, said Anderson.

The use of chemical dispersants during the oil spill coupled with the ultraviolet exposure in the Gulf may have increased the formation of OPAHs beyond expected levels.