Reconnaissance soil gas radon survey in Campania region (Italy): Preliminary results

Radon is a natural radioactive gas and it can be found in soils and rocks in the Earth, continuously produced by the decay chains of uranium, thorium, or actinium series. Thus, the radon potential for a given area is mainly the result of a combination of soils and underlying rocks properties. The presence of radon implies a serious human health risk, primarily related to lung cancer. Campania region territory (Southern Italy) is characterized by the occurrence of uranium (U) soil geochemical anomalies mainly associated to volcanic lithotypes. We have planned a regional project aimed at defining the concentration of 222Rn in soils of Campania region and the associated health hazard. This large-scale survey is based on a grid consisting of 158 cells (10 x 10 km). On the basis of estimated soil radon flux map of Campania region, we preliminary selected a sub-area characterized by an elevated geolithological variability. The soil gas radon survey was carried out in July 2019 in 15 sampling stations. In field measurements of radon concentration in soil-gas were performed using by connecting the radon measurement tools Alpha-GUARD PQ2000 PRO, Alpha-Pump, and soil-gas probe (inserted to a depth of 0.70 meter in the soil). In the circuit, operating in the flow mode, a pre-calibrated balloon of 1 L volume was included to control the quantity of gas and time during the filling process. After filling, the soil gas was isolated inside of the ionization chamber for about further 10-15 minutes such that 220Rn (Thoron), a short-lived isotope of radon with half-life of 55 seconds, could decay and the contribute of 222Rn be obtained. The radon index (RI) classification was obtained combining measured radon data and soil permeability data derived from grain size analysis. Our results showed that the distribution of 222Rn values ranged from 1 KBq/m3 to 95.1 KBq/m3. We found that radon spatial variability followed a NE-SW direction apparently shaping the geolithological features of the investigated area. For instance, measures performed where pyroclastic covers and major uranium contents in soils occur (>3.32 ppm) showed the highest radon levels (>76 KBq/m3). The hazard classification (RI) revealed that the intrinsic permeability of soils affect the amount of radon that potentially may exhales and indirectly can represent a hazard for indoor environments. From an experimental point of view, the adopted methodology proved to be a suitable approach for determining the concentration levels of radon in soil and allowed to discriminate the thoron contribution. Our findings represent a valid preliminary tool for the management of mitigation measures in health protection perspective. However, studies on a wider scale would serve as an important planning instrument at regional level. In our opinion, the proposed method for assessing the risk of radon exhaling from the underlying soil or bedrock have to be considered by all radon specialists since radon determination of building sites has become obligatory in EU countries with European Directive 2013/59/EURATOM.