The Galician Radon Map: Determining Indoor Radon Exposure Through Census Tracts

Abstract

Indoor radon is a human lung carcinogen. The objective of this research is to describe residential radon distribution in a European region with high geogenic radon potential using cross-sectional data. This study is also aimed at describing the use of census tracts as a geographical unit in radon maps and describing radon distribution according to floor level. To do this, 6080 radon measurements were carried out by the Galician Radon Laboratory (GRL, https://www.radon.gal) with alpha track detectors located at each dwelling for at least 3 months. The dwellings measured were the primary residences of volunteer participants. All participants filled out a questionnaire on the dwelling characteristics, and a follow-up call assured the appropriate return of radon devices to the GRL. A descriptive analysis was performed, including radon concentration distribution per floor level measured and a Galician map of indoor radon using both municipalities and census tracts as geographic units was made. In Galicia, a median radon concentration of 132 Bq/m³ (interquartile range: 66–239 Bq/m³) and a geometric mean (GM) of 126 Bq/m³ were observed. Eighteen percent of dwellings exceeded 300 Bq/m³. Radon levels vary widely across and within municipalities. The latter can be observed with census tract-level maps. A height gradient for radon concentration was observed from a GM of 289 Bq/m³ in cellars to a GM of 89 Bq/m³ on the fifth floor and above. Remarkably, 14% of dwellings on the second floor exceeded 300 Bq/m³, thus challenging the paradigm that indoor radon is only a priority for underground and ground levels in radon priority areas. Galicia is mostly composed of radon priority areas, with high heterogeneity in indoor radon distribution. Census tracts can be used in indoor radon maps as the smallest geographic unit to increase resolution and acknowledge variations within municipalities. In radon priority areas, radon surveillance should include second-floor levels.