Radon-222 has been classified by International Agency for Research on Cancer as being carcinogenic to humans, and as a gas that can be inhaled; lung cancer is a particular concern for people exposed to high levels of radon for sustained periods of time. During the 1940s and 50s, when safety standards requiring expensive ventilation in mines were not widely implemented, radon exposure was linked to lung cancer among non-smoking miners of uranium and other hard rock materials in what is now the Czech Republic, and later among miners from the Southwestern United States.

Since that time, ventilation and other measures have been used to reduce radon levels in most affected mines that continue to operate. In recent years, the average annual exposure of uranium miners has fallen to levels similar to the concentrations inhaled in some homes. This has reduced the risk of occupationally-induced cancer from radon, although health issues may persist for those who are currently employed in affected mines and for those who have been employed in them in the past. Of course, as the relative risk for miners has decreased, so has the ability to detect excess risks among that population.

Radon exposure (actually radon progeny) has been directly linked to lung cancer from numerous case-control studies performed in the United States, Europe and China. 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. North American and European Pooled analyses further support these findings. Further studies may be needed to assess the relationship between radon and leukemia.

The effects of radon if ingested are similarly unknown, although studies have found that its biological half-life ranges from 30–70 minutes, with 90 percent removal at 100 minutes.

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