Indoor radon risk mapping of the Canary Islands using a methodology for volcanic islands combining geological information and terrestrial gamma radiation data.

Within the framework of the recent approval of the National Plan Against Radon by the Council of Ministers of the Spanish Government, one of its five axes focuses on the delimitation of priority action areas. In line with this objective, this paper presents the indoor radon risk maps of the Canary Islands. Due to the volcanic origin of the Canary Islands, there is a great deal of geological heterogeneity in the soils on which buildings settle, making it very difficult to delimit radon-risk areas in the process of creating maps. Following a methodology developed in previous works for a study area formed of a set of representative municipalities, this paper presents radon risk maps of the Canary Islands based on lithostratigraphic information and high-resolution terrestrial gamma radiation maps. The goodness of fit of these maps is verified based on a statistical analysis of indoor radon concentration measurements carried out at representative building enclosures. In order to analyse the level of risk to the population, these maps were combined with built up areas (urban fabric) maps and estimations of the annual effective doses due to radon was obtained by applying a dosimetric model. This methodology improves the capability to delimit indoor radon risk areas, with a greater margin of safety. In this respect, it is estimated that areas classified as low risk have indoor radon concentrations 41 % below the current reference level of 300 Bq/m established by national regulations in compliance with the precepts laid down in the European EURATOM Directive.