People living or working near active natural gas wells where fracking takes place may be exposed to unsafe levels of certain air pollutants, a US scientific study has claimed.
Scientists from Oregon State University and the University of Cincinnati found that hydraulic fracturing a technique for releasing natural gas from below-ground rock formations emits PAHs (polycyclic aromatic hydrocarbons), some of which are linked with an increased risk of cancer and respiratory ailments.
Co-author of the study, OSU environmental chemist Kim Anderson, said: Air pollution from fracking operations may pose an under-recognised health hazard to people living near them.
The study, which appears in the online journal Environmental Science & Technology, is part of a larger project co-led by Kim Anderson and several of her colleagues from OSU, as well as the University of Cincinnatis Erin Haynes.
The team collected air samples from sites near active natural gas wells in Carroll County, Ohio, over a three-week period February 2014. The area sits on top of a deep oil-and-gas-rich reef of subterranean shale and is a hotspot of natural gas prospecting, with more than one active well site per square mile.
Researchers placed aluminium T-shaped air samplers on the properties of 23 volunteers living or working at sites ranging from right next to a gas well to a little more than three miles away. The samplers contained specially-treated polyethylene ribbons that absorb contaminants in a similar manner to biological cells.
The samplers picked up high levels of PAHs across the study area. Levels were highest closest to the wells and decreased by about 30% with distance, the results showed.
And, the scientists said: Even the lowest levels detected on sites more than a mile away from a well were higher than previous researchers had found in downtown Chicago and near a Belgian oil refinery. They were about 10 times higher than in a rural Michigan area with no natural gas wells.
The team also accounted for the influences of wood smoke and vehicle exhaust, common sources of airborne pyrogenic PAHs. Wood smoke was consistent across the sampling area, supporting the conclusion that the gas wells were contributing to the higher PAH levels.
The researchers then used a standard calculation to determine the additional cancer risk posed by airborne contaminants over a range of scenarios. For the worst-case scenario (exposure 24 hours a day over 25 years), they found that a person anywhere in the study area would be exposed at a risk level exceeding the threshold of what the US Environmental Protection Agency (EPA) deems acceptable.
However, Kim Anderson cautioned that these numbers are worst-case estimates and cant predict the risk to any particular individual: Actual risk would depend heavily on exposure time, exposure frequency and proximity to a natural gas well.
We made these calculations to put our findings in context with other, similar risk assessments and to compare the levels we found with the EPAs acceptable risk level.