Evaluating overestimated radon risk in predictive maps: A case study of cáceres municipality

Radon is recognised as the second most significant contributor to lung cancer incidence after smoking. Radon exposure to the general population usually takes place at home, where people spend a significant part of the day. Public policies have been established to achieve effective radon management based on radon maps, based either on indoor radon measurements or on soil properties. The Spanish predictive radon map is an example of the latter and is used to assess the potential radon risk. However, some areas present complex lithologies, such as Cáceres municipality, and are classified as a high radon risk area, with the 90^th percentile of the distribution (P₉₀) of indoor radon concentration higher than 400 Bq m^-3. In this study, an indoor radon measurement campaign was carried out in all population settlements in Cáceres municipality, obtaining a log-normal indoor radon distribution with a geometric mean of 111 Bq m^-3. The P₉₀ was 318 Bq m^-3, slightly above the reference level of 300 Bq m^-3. Indoor radon concentration depended on the lithology. Buildings located on a zone with limestone and slates from the Lower Carboniferous presented lower radon concentrations, whereas buildings located on weathered granites areas showed higher concentrations. Discrepancies between the P₉₀ value estimated in this study and that considered in the Spanish predictive radon map can be attributed to the fact that the latter considered all the area comprised by the municipality (mainly granitic); while we only considered the populated areas within it (located on various lithology types). Therefore, the Spanish predictive radon map can be considered as conservative and slightly overestimated the actual risk to radon exposure in the case study.