People who live in close proximity to natural gas drilling sites are significantly more likely to report skin and respiratory problems than those who live further away, according to the largest survey to-date of the reported health effects of people exposed to fracking.

The study, "Proximity to Natural Gas Wells and Reported Health Status,"(pdf) published Wednesday in the journal Environmental Health Perspectives surveyed households with ground-fed water wells located in the Marcellus shale region in southwestern Pennsylvania.

Researchers found that 39 percent of households located less than one kilometer from an active natural gas well reported upper respiratory problems, compared with 18 percent located more than 2 kilometers away. Further, 13 percent of respondents who live within a kilometer of a well said they had rashes and other skin irritations, compared with just 3 percent who live more than 2 kilometers away.

Of the 624 active natural gas wells located in Pennsylvania's Washington County, 95 percent were fracked — or injected with millions of gallons of water, sand, and a largely-unknown toxic mix of chemicals in order to extract gas from the shale deposits.

Despite assurances by the drilling industry and numerous government officials that fracking chemicals do not pose a risk to nearby populations, scientists and environmentalists have repeatedly voiced concern over the high volume of chemicals used in the process and the potential for both groundwater and airborne contamination. Further, the drilling industry has long-fought efforts to reveal the particular chemicals used in fracking, claiming that the combination of toxins fall under "proprietary information."

The Yale-based research team notes that they did not collect data on whether individuals were receiving financial compensation for gas well drilling on their property, which they acknowledge "could have affected their willingness to report symptoms."

Based on the findings of the survey, the researchers conclude that "airborne irritant exposures" related to natural gas extraction activities, including the flaring of gas wells and exhaust from diesel equipment, "could be playing a role" in the increased reporting of respiratory symptoms among people living in close proximity to the wells.

Possible explanations for the increase in reported skin irritations also include exposure to air pollutants, as well as possible well water contamination due to "breaks in the gas well casing or other underground communication between ground water supplies and fracking activities."

Because of the relative newness of the wells (5-6 years), the researchers were unable to test for a correlation between drilling activities and more long-term health impacts, such as cancer. However, the team says that their findings underscores the need for further research on the possible health impacts of fracking activities, including longitudinal studies on chronically exposed populations.