The United States leads the world in natural gas production and that status is in no small part due to the boom in fracking in places like northeast Pennsylvania, which sits atop the Marcellus shale formation.
As much as boosters of domestic fossil fuel production have pointed to the economic benefits of fracking, critics of the drilling technique have warned of its environmental and public health impacts.
A new study by researchers at the University of Pennsylvania and Columbia University lends credibility to those concerns. They found that hospitalization rates were higher in the region's most heavily fracked areas, with residents more likely to visit the hospital for a range of ailments if they lived in close proximity to natural gas wells.
"This study was somewhat surprising to us because we didn't have any preconceived notion —we were proving or disproving a relation between hospital visits and fracking," Reynold Panettieri Jr., one of the study's authors and a professor of pulmonary medicine at the University of Pennsylvania, told VICE News.
Panettieri and his colleagues analyzed 90,000 hospitalization records for the years 2007-2011in the northeastern Pennsylvania counties of Bradford, Susquehanna, and Wayne. Bradford and Susquehanna had a high number of fracked wells, while Wayne acted as a control group, since there were no active wells in the county.
The researchers found that inpatient cardiology visits were about 27 percent more frequent in zip codes with many fracking wells — defined as more than 79 wells per 100 square kilometers —than in zip codes with no wells. Dermatology visits, meanwhile, were 45 percent more frequent in the fracking zip codes than in areas with no wells.
"Now the drilling continues at a growing rate —it's grown exponentially in the years 2011-2014," Panettieri said. "And until recently the cost to human health was not examined."
Watch the VICE News documentary "Toxic Waste in the US: Coal Ash" here:
The study's findings only prove correlation, not causation, Panettieri noted, but he said other research suggests the spurt of health issues, indeed, arises from fracking. The clearest cause of cardiovascular problems appeared to be fumes from the trucks trafficking materials into and out of the fracking zones, he said.
"Everything that comes into a fracking zone has to be trucked in and trucked out, so these areas, which are relatively rural, are exposed to fumes," Panettieri said.
A March study found that people living close to busy traffic corridors were exposed to greater concentrations of C-reactive protein, a known cause of cardiovascular diseases.
Toxins from drilling released into the air and water in fracking zones could also contribute to the increased hospitalization rates, Panettieri said. Researchpublished in 2011, for instance, found that up to 75 percent of the chemicals used in natural gas operations are harmful to the skin, eyes, and other sensory organs.
"What our study has done is identify specific diseases [that are correlated to fracking]. Now we need to understand the toxins or combination of toxins that contribute to these diseases," Panettieri said, adding that he and his colleagues will further unpack their data and publish additional studies.
Their research, published in the journal PLOS One, adds to a growing body of work implicating fracking operations in increased rates of some human health problems.
University of Pittsburgh researchers found that mothers living close to the drilling activity in Marcellus shale were more likely to give birth to underweight babies. And researchers from the Colorado School of Public Health and Brown University found that babies in highly fracked regions of Colorado more frequently had birth defects.
Jason Hutt, an attorney with Bracewell & Guliani representing the fracking industry in the region, told VICE News the study did not prove fracking caused any health risks.
"The study shows a correlation but that doesn't necessarily mean there's a causation," said Hutt. "Pennsylvania's fracking regulations are some of most progressive regulations in country to ensure well integrity, which would reduce the risk of public health concerns."
He also noted that the US Environmental Protection Agency recently released a study that found fracking did not cause a "widespread risk" to drinking water. And, Hutt said, there are no proven health risks from fumes released during drilling.
"There's nothing that comes out of the well itself that is a hazardous air pollutant," he said.
Panettieri's findings were no surprise to Marcellus shale locals, though, who told VICE News they hoped the research would prompt more stringent fracking regulations in the state.
Rebecca Roter, who co-founded the group Breathe Easy Susquehanna County to fight for better air quality monitoring in fracking zones, complained of truck traffic, poor air and water quality, and even occasional explosions at the compressor stations that pressurize gas in order to be transported through pipelines.
"It's been incredibly frustrating because there has been no independent documentation on fracking's impact on air quality or health," Roter told VICE News. "I was extremely happy to see that [the researchers] came out with this hard, high validity study that speaks to our conditions now before there are worse impacts."
Roter noted that fracking wells are often located near schools, hospitals, and residential areas.
"I am hoping that policy makers look at this finding," she said, "because they have a chance to do the right thing."
A spokesman for Pennsylvania's Governor Tom Wolf maintained that he had taken numerous steps to strengthen oversight of fracking industry since taking office in January.
"Protecting our environment and the health of all Pennsylvanians is Governor Wolf's top priority," press secretary Jeff Sheridan told VICE News.
Sheridan said Governor Wolf proposed $10 million for more Department of Environmental Protection regulators, and proposed to create a health registry for complaints from the public.
The PA legislature is considering Wolf's proposals.
Sheridan said the DEP was currently reviewing the health study, and would take action if it confirmed negative health impacts had occurred due to fracking.
"Pennsylvania is committed to a process of continuous improvement so that shale gas development is following best practices," Sheridan said. "The Wolf administration believes that shale gas drilling can be done in an environmentally sound and safe manner that protects public health. Where we find evidence that development is causing negative impacts, the administration will not hesitate to step in to protect the public."
Follow Meredith Hoffman on Twitter: @merhoffman