Radon. A naturally radioactive element with atomic symbol Rn, atomic number 86, and atomic weight 222. It is a member of the noble gas family and released during the decay of radium and found in soil. There is a link between exposure to radon and lung cancer.
A gas that occurs naturally as the by product of the decay of naturally occuring uranium. The gas is both odourless and colourless. Although named a s aknown carcinogen by the EPA it is only ever found in small quanitites and no side effects have been noticed even after prolonged exposure.