A new study in Ohio found that indoor radon levels increase the closer a home is to fracking operations. The concentration of radon gas in households is the second leading cause of lung cancer in the U.S.

Researchers from the University of Toledo (UToledo) analyzed data obtained from the Ohio Radon Information System (ORIS), a publicly accessible database that the university has been developing over the past 25 years. The study included 118,421 homes, spanning all counties in Ohio, between 2007 and 2014.

The scientists were able to make the link between the increase in radon levels and proximity to the 1,162 fracking wells in the state by measuring and geocoding the data. In addition, they found that all the homes tested had higher radon levels, an average of 5.76 picocuries per liter (pCi/l), than is deemed safe by the U.S. Environmental Protection Agency (EPA) and the World Health Organization. The EPA threshold is 4.0 pCi/l. The highest level found for this data set, a concentration of 141.85 pCi/l, is in the city of Stryker, located in the northwest corner of Ohio.

"The shorter the distance a home is from a fracking well, the higher the radon concentration. The larger the distance, the lower the radon concentration," said Dr. Ashok Kumar, Distinguished University Professor and chair of the UToledo Department of Civil and Environmental Engineering.

Radon, an invisible and odorless gas, comes from decaying uranium found naturally in soil, water and rocks. Fracking is the process of injecting pressurized liquid into a rock formation for the purpose of extracting natural gas.

Dr. Yanqing Xu, assistant professor in the UToledo Department of Geography and Planning, explained that the motivation behind the study “is to save the lives of Ohioans” by inspiring them to have their homes tested for radon and, if necessary, install mitigation systems.

The results of the study were recently published in the journal Frontiers in Public Health.