A congressional probe has found oil and gas corporations involved in the drilling practice of hydrofracking injected hundreds of millions of gallons of dangerous chemicals into wells in more than a dozen states from 2005 to 2009. The chemicals were used in the fluids used to open up deposits of natural gas deep below ground. The U.S. House Energy and Commerce Committee also found that companies used at least 650 products that are known or possible human carcinogens, or are hazardous air pollutants.