From collective to individual radon risk exposure: An insight into the current European regulation.

Radon (Rn) is a radioactive gas with well-documented harmful effects; the World Health Organization has confirmed it as a cancerogenic for humans. These detrimental effects have prompted Europe to establish national reference levels to protect the exposed population. This is reflected in European directive 59/2013/EURATOM, which has been transposed into the national regulations of EU Member States. Specifically, the directive requires the identification of Radon Priority Areas to facilitate remediation in regions with high Rn levels. The regulation also includes measures for radiation protection, aiming to safeguard the population collectively and individuals from Rn exposure. These two requirements can be conceptualised and translated into two complementary concepts: collective and individual risk. This work addresses the lack of a standardised methodology at the European level for defining radon (Rn) risk across regions. It provides the first approach to transitioning from collective to individual risk areas (CRAs to IRAs), offering clear insights into the application of European Rn protection regulations. Key challenges have been addressed, including geo-hazard mapping without a response variable, evaluating the performance of Spatial Multi-Criteria Decision Analysis, and assessing the use and representativeness of available indoor Rn data to support individual risk assessment. The study also explores the optimal scale for delineating Radon Priority Areas. The effectiveness of this novel approach, which incorporates both collective and individual risk factors in accordance with European regulations, has been tested in a case study in the Bolzano province (north-eastern Italy).