 Radon exposure (mostly radon daughters) has been linked to lung cancer in numerous case-control studies performed in the US, Europe and China.There are approximately 21,000 deaths per year in the US due to radon-induced lung cancers.One of the most comprehensive radon studies performed in the United States by Dr. R. William Field and colleagues found a 50% increased lung cancer risk even at the protracted exposures at the EPA's action level of 4 pCi/L.