Radon exhalation across the Periadriatic Lineament in the Pustertal/Pusteria Valley (Bolzano, North-Eastern Italy).

In the early 90's, the Environmental Protection Agency of the Bolzano Province (NE Italy) performed a study on Indoor Radon in all the municipalities of the district (Minach et al., 1999). The aim of these measurements was to identify the areas characterized by high Indoor Radon (IR) values to realize an Indoor Radon map. Most of the municipalities that resulted to have average IR values above 400 Bq/m3, thus classified at high risk according to 90/143/EURATOM, are aligned along the Pustertal/Pusteria Valley. In this work, the relation between Radon activity, and the concentrations of other gases in the soil, and geological factors (e.g. lithology, tectonic structures) is investigated along two profiles across the Periadriatic Lineament in the Pustertal/Pusteria Valley. Samples of the petro-volumetrically relevant lithologies of the studied area have been collected, their chemical composition (XRF) and their radionuclides content (high resolution gamma-rays spectrometry) determined. The lithologies include granitoid rocks, orthogneisses, micaschists and phyllites, some of which are characterized by a high activity concentration of natural terrestrial radionuclides. As a consequence, their presence in the study area may potentially increase Radon emission (EC-JRC, 2019). Radon, CO2, CH4, O2, H2and H 2S have been measured in soil gas along the two profiles to investigate the effect of the Periadriatic Lineament (PL) on Radon exhalation. The profiles are located near Mühlen/Molini (P1) and Pfalzen/Falzen (P2), respectively. Preliminary results show two evident Radon peaks of 112 kBq/m3and118 kBq/m 3along P1, and of 148 kBq/m 3 and 157 kBq/m3along P2. The background values are below 50 kBq/m 3. These peaks correspond to two main cataclastic zones of the Periadriatic Fault system mostly buried under quaternary loosen sediments. Thus, cataclastic zones represent preferential paths for Radon mobility and exhalation. The comparison of the IRdistribution map, the geochemical composition of the main lithologies and the results from the in-situmeasures, clearly indicate that, although outcropping lithologies represent an important factor contributing to the IRvalues, they cannot justify such high IRvalues measured in the buildings alone. Instead, the structural features of the Periadriatic Fault system play a key role in enhancing radon exhalation, exposing to potential radon risk specific areas within the territories of the municipalities located in the Pustertal/Pusteria Valley.