Hydraulic fracturing, commonly known as fracking, may be increasing levels of toxic radon in Pennsylvania homes, according to a new study.

Since the practice began around 2004, the state has seen 42 percent of radon readings surpass what the US government considers safe.

What's more, buildings located in the counties where natural gas wells are most actively being drilled have in the past decade seen significantly higher readings of radon compared with buildings in low-activity areas - a phenomenon that did not exist prior to 2004.

"One plausible explanation for elevated radon levels in people's homes is the development of thousands of unconventional natural gas wells in Pennsylvania over the past 10 years," study lead author Brian S. Schwartz, with the Johns Hopkins Bloomberg School of Public Health, said in a statement. "These findings worry us."

Radon is an odorless radioactive gas that is considered the second-leading cause of lung cancer in the world after smoking.

In order to figure out the potential impact fracking may have on radon exposure in Pennsylvania, the researchers analyzed more than 860,000 indoor radon measurements included in a Pennsylvania Department of Environment Protection database from 1989 to 2013. They then evaluated associations of radon concentrations with geology, water source, season, weather, community type and other factors.

Between 2005 and 2013, nearly 7,500 unconventional natural gas wells were drilled in Pennsylvania via fracking to free natural gas from shale.

Until now, most natural gas was obtained through conventional natural gas wells - this is when wells are created by drilling vertically into porous zones of rock formations like sandstone to release the gas. However, recently there has been a surge in the drilling of unconventional natural gas wells in 18 states throughout the country.

In contrast to the conventional wells, gas is not sitting in shale waiting to be pumped out. Instead, the gas is contained in the shale, which needs to be broken apart to release large volumes of natural gas. This is done by first drilling deeper into the ground vertically and again horizontally. Then, during the fracking process, millions of gallons of water containing various chemicals are pumped in to help extract the gas. Previous research has warned that this fracking flowback may even lead to contaminated groundwater. (Scroll to read on...)

Not only does this disruptive process bring gas back to the surface during well development, but it also brings heavy metals and organic and radioactive materials with it. This includes radium-226, which decays into radon, and has been found in well water, natural gas and ambient air.

During the course of the study, Schwartz and his colleagues realized that houses and other buildings using well water had a 21 percent higher concentration of radon than those using community water. Also, houses and buildings located in rural and suburban townships, where most of the gas wells are, had a 39 percent higher concentration of radon than those in cities.

The findings were reported in the journal Environmental Health Perspectives.

According to the researchers, they are not sure exactly how radon is accumulating in public buildings and people's homes - putting them at an increased risk for lung cancer. It could be that the excess radon is coming from radium getting into well water through the fracking process, or it's being released into the air near the gas wells. Another possibility is that natural gas from shale contains more radon than conventional gas and it enters homes through cooking stoves and furnaces.

Regardless, it seems that fracking may be playing an important part in these increased indoor radon levels.

"By drilling 7,000 holes in the ground, the fracking industry may have changed the geology and created new pathways for radon to rise to the surface," added first author is Joan A. Casey. "Now there are a lot of potential ways that fracking may be distributing and spreading radon."

It should be noted that the state of Pennsylvania recently took a comprehensive set of measurements near 34 gas wells, including air samples for radon near four wells, and they did not show high levels of the radioactive gas. However, the researchers claim their study is a better way to assess the potential cumulative impacts of all the wells, given that they studied radon levels in hundreds of thousands of homes and other buildings.

"I don't think we can ignore these findings," Schwartz concluded. "Our study can be improved by including information that was not available for our analysis, such as whether natural gas is used for heating and cooking, whether there is any radon remediation in the building, and general condition of the building foundation. But these next studies should be done because the number of drilled wells is continuing to increase and the possible problem identified by our study is not going away."

With global warming on the brain, experts are looking towards other renewable means of accessing fuels so as to reduce our carbon footprint. As a result, the fracking boom has soared to new heights. (Scroll to read on...)

According to recent research, shale-gas production is expected to surge in the next three decades. Between 2005 and 2013 alone, some 82,000 fracking wells were drilled into the shale deposits beneath 17 states, according to the environmental advocacy group Environment America.

This could be extremely dangerous, considering that experts have yet to fully understand the environmental impacts this practice could cause.

For instance, only does fracking supposedly contaminate groundwater as well as have an impact on animals, but it also may result in micro-earthquakes normally too insignificant for humans to notice.

However, in March 2014 a rare earthquake was actually felt by residents in Poland Township, Ohio. Fracking activated a previously unknown fault, triggering a series of five recorded earthquakes, ranging from magnitude 2.1 to 3.0. Some believe this evidence supports the idea of including fracking in earthquake hazard assessments.

While fracking has its pros and cons, more and more the practice is coming under scrutiny. The only thing we can be certain of now is that more research is needed to better understand if fracking indeed poses a threat to our future.

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