A leading environmental group says fracking causes toxic air pollution. According to a report released Tuesday by the National Resources Defense Council, Americans who live near oil and gas drilling operations are exposed to a variety of hazardous airborne chemicals including benzene and formaldehyde. Researchers say those chemicals can cause breathing problems, birth defects and cancers, among other serious health issues. Previous studies by the EPA have linked fracking to pollution of drinking water. The drilling process uses huge amounts of water mixed with sand and other chemicals to break apart shale deposits to extract gas and oil.