Newly released documents reveal that the Environmental Protection Agency had concerns that chemicals used in horizontal hydraulic fracturing of oil and gas wells could cause serious health problems for people living near wells, but allowed the chemicals to be used anyway.

The EPA approved more than 40 drilling and fracking chemicals with known health risks between 2003 and 2014, and only requested chemical safety tests for less than 10 percent of them. "What risks? Agency documents list poisoning of the brain, lungs and liver; tumors; poor development in infants and fetuses," Scott Tong reports for Marketplace.

Bryan Latkanich, who lives in rural Pennsylvania, sold Chevron the right to drill on his property seven years ago, but he says he thinks improperly stored fracking chemicals in the water made his young son Ryan ill. When Ryan was 7, he took a bath and immediately became covered in rashes that Latkanich says were "beyond poison ivy or oak." Since that bath, Ryan has been diagnosed with asthma and regularly loses bowel control. "Latkanich himself has been diagnosed with neuropathy, a kind of nerve damage that causes him joint pain," Tong reports. Latkanich's claims may not be without reason: the state of Pennsylvania found that Chevron illegally dumped fracking water on his property.

It's difficult to prove cause and effect for chemical exposure, since health problems may not occur until years later, but several studies show that people who live near fracking wells are more prone to have cancer, asthma, high-risk pregnancies and heart defects.