Exposure to atmospheric radon

We measured radon (Rn-222) concentrations in Iowa and Minnesota and Found t hat unusually high annual average radon concentrations occur outdoors in po rtions of central North America. In some areas, outdoor concentrations exce ed the national average indoor radon concentration. The. general spatial pa tterns of outdoor radon and indoor radon are similar to the spatial distrib ution of radon progeny in the soil. Outdoor radon exposure in this region c an be a substantial fraction of an individual's total radon exposure and is highly variable across the population. Estimated lifetime effective dose e quivalents for the women participants in a radon-related lung cancer study varied by a factor of two at the median dose, 8 mSv, and ranged up to 60 mS v (6 rem). Failure to include these doses can reduce the statistical power of epidemiologic studies that examine the lung cancer risk associated with residential radon exposure.