Radon is a radioactive gas that emanates from rocks and soils and tends to concentrate in enclosed spaces, such as underground mines or houses. Radon can be found buildings of all kinds. Soil gas infiltration is recognized as the most important source of residential radon. Other sources, including building materials and water extracted from wells, are less important in most circumstances. Radon is a major contributor to the ionizing radiation dose received by the general population.
Studies on indoor radon and lung cancer in Europe and North America provide strong evidence that radon causes a substantial number of lung cancer cases in the general population. The analyses indicate that the lung cancer risks increase proportionally with increased radon exposure. As many people are exposed to low and moderate radon concentrations, most lung cancer related to radon are caused by these exposure levels rather than by higher concentrations. Radon is the second-leading cause of lung cancer after smoking. Most of the radon-induced lung cancer cases occur among smokers due to a strong combined effect of smoking and radon. A national reference level for radon represents the maximum accepted radon concentration in a residential dwelling. The EPA strongly urges remediation or action be taken in homes with a radon level at or above 4pCi/L (picocuries per liter) to reduced exposure. Because there is no known safe level of exposure to radon, the EPA also recommends that Americans consider fixing their home for radon levels above 2 pCi/L. The average indoor radon level in North America in 1.3 pCi/L as compared to the average outdoor of .4pCi/L.
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