Radon revisited.  The early warnings may have been overblown, but research since has shown that lung cancer risk from the gas is real.
D000396:Air Pollutants, Radioactive / Q000633:toxicity*; D006798:Housing; D008175:Lung Neoplasms / Q000209:etiology*; D008906:Mining; D009381:Neoplasms, Radiation-Induced / Q000209:etiology*; D011886:Radon / Q000633:toxicity*
D000396:Air Pollutants, Radioactive; D011886:Radon