Hydraulic fracturing activities to extract natural gas can release carcinogenic polycyclic aromatic hydrocarbons (PAHs) into the air, a new study shows (Environ. Sci. Technol. 2015, DOI: 10.1021/es506095e). In some cases, the estimated exposure of nearby residents to these compounds exceeded the Environmental Protection Agency’s maximum acceptable risk level for cancer.
Many researchers and community leaders are concerned about the human health impacts of air and water pollution from hydraulic fracturing, often called fracking, and the limited environmental regulation of the industry in the U.S. Fracking can release carcinogens such as benzene into the air along with other volatile organic compounds that are precursors of smog, which can contribute to asthma and other respiratory illnesses (Sci. Total Environ. 2012, DOI: 10.1016/j.scitotenv.2012.02.018).
But few studies have examined the impact of fracking on airborne PAHs, larger molecules that are also linked with cancer and respiratory illness (Atmos. Environ. 2008, DOI: 10.1016/j.atmosenv.2007.12.010). The compounds are present in fossil fuels and are also products of their combustion—for example, they’re found in the exhaust of truck traffic near fracking sites.
Kim A. Anderson, a researcher at Oregon State University, wanted to understand how these compounds might affect workers and residents near fracking operations. So she and her colleagues designed a citizen-science study in Carroll County, Ohio, a community with especially high fracking activity. As of June 2014, the county had 421 natural gas drilling leases, a density of more than one well per square mile. Many community members were concerned about their health impacts, Anderson says.
In February 2014, Anderson and colleagues installed passive air samplers on the properties of 23 volunteers living within 3 miles of active wellheads in the county. The samplers included low-density polyethylene strips to absorb the volatile compounds in air that a person would breathe in. After three weeks, the participants sent the samplers back to the lab in air-tight bags. The team analyzed the collected compounds for 62 PAHs using gas chromatography with tandem mass spectrometry. The researchers then calculated average total concentrations of a set of 14 PAHs for three groups of volunteers on the basis of how far they live from an active well: within 0.1 mile, between 0.1 and 1 mile away, and between 1 and 3 miles away.
For all three groups, the average total PAH concentrations were higher than those measured by a previous study in downtown Chicago and about 10 times greater than those measured in rural areas without fracking activity. The concentrations were 57% higher for the group that lived closest to a well than for the group that lived farthest away.
The researchers also examined the ratios of individual PAHs to determine whether they came from natural gas extraction or car exhaust. At sites closer to the wells, the main source of PAHs was the natural gas itself, whereas sites farther away showed a mixture of exhaust and natural gas signatures.
The researchers then estimated excess lifetime cancer risk for various levels of exposure to all the PAHs they measured using a standard EPA method. For maximum residential exposure of 350 days per year over 26 years, the calculated risk at every distance exceeded EPA’s acceptable range. In all the scenarios they considered, the excess risk for the group closest to wells was about 45% greater than that for the group farthest from them.
David O. Carpenter, an environmental health scientist and physician at the University at Albany, SUNY, says the study provides important new data on PAHs near fracking sites and supports the growing evidence that the process poses added health concerns to people living around the sites. He was surprised by the finding that PAHs are coming mainly from the natural gas itself, because earlier studies of the compounds near fracking sites assumed that vehicle exhaust was the main source. “It opens up a whole new area of research,” he says.
RETRACTION: The paper described in this article has since been retracted (Environ. Sci. Technol. 2016, DOI: 10.1021/acs.est.6b02342).
To read C&EN’s coverage of this retraction, click here.