Radon, the odorless gas that occurs naturally in soils and often finds its way into homeowners’ basements, is a familiar concern for people across Pennsylvania. According to the U.S. Environmental Protection Agency (EPA), radon is responsible for 21,000 cancer deaths in the U.S. every year, and Pennsylvania homes and buildings have some of the highest radon levels in the country. In fact, a full 40 percent of homes in the state have radon levels above what the EPA considers actionable.

The risks of radon and how it gets into our homes have been understood for decades. Radon starts out as uranium, which occurs naturally in soil and rocks. And as that uranium decays, it eventually becomes radon gas—which can then migrate into people’s basements. But there is some concern that unconventional natural gas development could be pushing Pennsylvanians’ radon exposure even higher.

LISTEN: Is Pennsylvania Natural Gas Increasing Your Radon Risk?

“The Marcellus is considered to be a fairly radioactive rock,” says Elizabeth Casman, a researcher in environmental engineering at Carnegie Mellon University.

The ‘Marcellus’—or Marcellus Shale—is the geological formation feeding the state’s fracking boom, and it has particularly high levels of radon. So when fracking in the region began, Casman wondered whether radon in the Marcellus could be making its way into the natural gas that fuels furnaces, water heaters and stoves in our homes.

“The more I was reading about the formation and the potential for radon in the natural gas, the more nervous I got,” she says.

In fact, Casman herself stopped cooking on her gas stove.

Researcher Elizabeth Casman at her CMU office

When Carnegie Mellon researcher Elizabeth Casman learned how radioactive the Marcellus Shale is, she got a little concerned that the natural gas coming into her home could be creating dangerous levels of radon. In fact, she initially declared a mini moratorium—forgoing cooking on her gas stove—until she studied the risks. Photo: Julie Grant

But sorting out exactly what percentage of home radon levels may be coming from Marcellus natural gas is tricky—in part, because Pennsylvania has such high radon levels to begin with.

“We have some of the most unique geology, soils and rocks—creating some of the highest radon levels naturally probably in the country, maybe the world,” says Dave Allard, who heads up the Bureau of Radiation Protection at the Pennsylvania Department of Environmental Protection (DEP).

He says home radon levels in Pennsylvania are also trending upward. His department has even seen some homes with levels 250 times the amount that’s actionable by EPA.

“Quite honestly, some of our residential levels in Pennsylvania are higher than you would allow in a uranium mine,” he says.

So the DEP started looking into whether natural gas could be responsible for these higher radon levels. Bob Lewis, the state’s chief radon officer, conducted tests at more than 30 wellheads in different parts of the state. The agency did similar sampling at natural gas power plants, compressor stations and storage facilities.

“And our conclusions show that [residents] were receiving small—very small—radiation doses from the radon in natural gas,” Lewis says.

“Quite honestly, some of our residential levels in Pennsylvania are higher than you would allow in a uranium mine.”

Initially, the DEP’s findings seemed to put the issue to bed: Though Pennsylvanians are still advised to test for radon in their homes, it didn’t appear that Marcellus Shale gas was adding to the problem.

But then, the state’s radon experts got blindsided. Researchers at Johns Hopkins University took a second look at DEP’s own data and spotted a potentially troubling trend. In a study published in Environmental Health Perspectives, they documented that the upswing in radon levels coincided with the start of the fracking boom.

“We wanted to see if this new industrial development potentially was contributing to increased levels of radon in homes,” says Joan Casey, lead author on the Hopkins study.

The researchers first broke up the state into different regions: places with no fracking, some fracking and high levels of fracking. They then analyzed more than 800,000 home radon tests, which are filed with the DEP.

“We saw at the same time that fracking was going on, increased levels of indoor radon in the places that had the most fracking,” she says.

They also looked at how a home or building’s proximity to fracking activity correlated with radon levels.

“And we found that buildings that were closer to more drilled wells had significantly higher indoor radon concentrations than buildings located farther away.”

But the DEP’s radon expert Dave Allard says those findings could unnecessarily scare people. For one, Allard points out that radon is trending up in every region of the state—no matter how close or far it is from fracking activity. To him, that indicates that there is likely some other cause. Allard’s thinks the uptick in radon levels is linked to increased soil moisture, which he says is backed up by a 2015 study from Finland.

But Casey says her analysis takes rainfall into account. And she says even the small increase in indoor radon that the DEP found is reason for concern.

“In terms of lung cancer risk, there’s no safe level of radon exposure,” Casey says. “And any increase in radon levels translates into an increased risk of lung cancer. That’s definitely true.”

Casey admits the Hopkins study doesn’t explain why radon levels are increasing. She says radon could be entering homes through well water, ambient air or the use of natural gas for cooking and heating.

As for Elizabeth Casman—the Carnegie Mellon professor who stopped cooking on her gas stove—she, like any good researcher, collected her own data. With an agreement from energy companies, she and her team took samples from some natural gas pipelines. And Casman says she was relieved by the findings.

“We took all the worst cases, and still it came out to a non-scary risk level,” Casman says. “And that’s when I calmed down about cooking.”

marcellus-gas-sites-map

Map showing seven locations where radon samples were collected by researchers at Carnegie Mellon University. Each sampling location is numbered and colored to correspond with measured radon concentration (red is highest). For Pennsylvania, county production only includes unconventional natural gas production. Map courtesy Carnegie Mellon University

Casman says unless someone used an unvented stove to heat their home, and they didn’t leave the house for 70 years, they won’t really have an elevated risk of lung cancer from Marcellus Shale gas.

“The increment from cooking is probably not going to be killing a lot of people,” she says.

Still, Casman and others say the issue deserves further study. But for now, if you’re concerned about radon from your gas stove, she says just open a window.

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This story is part of our series Follow the Pipeline, which explores the health and environmental impacts of the region's expanding natural gas infrastructure.