A recent analysis from SkyTruth has found that cancer-causing chemicals were used in about a third of fracking operations reported to FracFocus over a 21-month period in 2011 and 2012. The SkyTruth analysis reviewed more than 27,000 reports. The three most common carcinogens used in fracking were formaldehyde, naphthalene, and benzyl chloride. Check out the SkyTruth post for more details.