Radon monitoring in underground workplaces. The case of Sardinia region (Italy)

Among the main geological factors affecting human health there is the geogenic release of radon from soil and rocks that poses a serious risk of ionizing radiation exposure to the population. This natural radioactive gas can quickly diffuse underground and dissipate into the atmosphere or enter through cracks or open spots inside buildings, where it can be accumulated. In Italy, the indoor concentration of radon is regulated by Law 101/2020, which establishes a reference level of 300 Bq/m3 (200 Bq/m3 for dwellings constructed after 2024), expressed as the annual average value of radon activity concentration in the air. This regulation applies to indoor workplaces, specifically to all underground spaces. Measurements on the ground floor and in the basement are carried out only in the areas defined as at risk (the reference level is exceeded in 15% of buildings) by the Italian national and regional radon action plans. Currently, three Italian regions have an action plan in place to reduce the population's radon exposure. Since 2019, Sardinia has identified the radon priority areas with Dgr n. 7/49 including municipalities where the probability of exceeding the 300 Bq/m3 level exceeds 30% of the buildings, recently updated with the requirements of the national reference level (Dgr n. 20/71 of 2022). Considering that the distribution of financial services over a region depends on population density and economic activities, in this study data from radon concentration measurements in some underground workplaces of different bank companies in Sardinia were analysed as a possible criteria for radon risk assessment. Radon activity measurements from 36 bank buildings located in 17 municipalities spread throughout the island were collected. The CR-39 detectors were exposed in a total of 262 indoor spaces, used by employees and/or accessible to the public. The duration of the monitoring was two or more consecutive periods (e.g., two semesters) to cover an entire solar year of exposure, otherwise, the dosimeter was directly exposed for an entire year. In some cases, multiple data were recorded for a single room, depending on its volume, and a weighted average of the different measurements was determined. The annual concentrations recorded in the last 10 years range from 8 to 1,630 Bq/m3. The analyses show that only approximately 6% of the monitored rooms exceed the limit set by Italian regulations. Among those underground workspaces that exceed the reference level, not all are located into Sardinian priority areas. Furthermore, data exploration shows that in some buildings there is high variability between rooms belonging to the same floor. These results hint at the difficulty of accurately predicting indoor radon concentrations and highlight the importance of performing radon monitoring to protect workers’ and public’s health.