The role of Pusteria fault zone (North-Eastern Alps, Italy) on enhancing the Geogenic Radon component

Radon (222Rn) is a radioactive gas widely considered an indoor air pollutant due to its harmful effects on human health (WHO, 2009). The Geogenic Radon Potential (GRP) quantifies what "Earth delivers" in terms of radon and represents the most important contributor to Indoor Radon Concentrations (IRC) indicating the potential risk over an area (Bossew 2015). This is the special case of some municipalities in Pustertal/Pusteria Valley (Bozen/Bolzano, North-Eastern Italy) which display a high IRC, based on Indoor measurements carried out by Minach et al. (1999), exceeding the threshold value recommended by EURATOM 59/2013. These municipalities are located along a wide brittle-fracture zone between the Pusteria Line (PL, the eastern part of Periadriatic Lineament) and the Deffereggen-Anterselva-Valles (DAV) faults. This fractured zone may act as preferential pathway for radon transport and migration by carrier gases (mainly CO2 and CH4), strongly contributing to its geogenic component. A GRP map of the study area has been developed based on field measurements of radon, thoron (220Rn) and other soil gases (CO2, CH4, H2, O2, H2S) according to a sampling grid in an area of 6x10 km, and along three profiles crossing above mentioned fault lines in Terenten/Terento, Mühlen/Molini and Pfalzen/Falzes specific areas. The GRP map was constructed by using soil gas radon data and other proxy variables in a spatial regression model. Soil gas measurements have been supported by high-resolution gamma-ray spectrometry on 16 rock samples belonging to the main outcropping lithologies in the study area i.e. granite, orthogneiss, micaschist-paragneiss, phyllite. The preliminary radon map highlights a wide area of radon anomaly located to the North of the Periadriatic Lineament. The global trend of these radon anomalies follows the structural trend of the brittle fracture zone between PL and DAV faults and tends to close from the eastern part (Pfalzen/Falzes) toward the western part (Terenten/Terento) of the study area. In particular the easternmost sector of the map displays a wide north-south area of radon anomaly related to a wide brittle-fracture zone probably composed by a system of sub-parallel faults. The spatial distribution of radon anomalies confirms the key role played by the Pustertal/Pusteria fault system in the fluid degassing processes enhancing geogenic radon potential of the Pustertal/Pusteria Valley. Keywords: Natural Radioactivity, Geogenic Radon Potential, Indoor Radon, Periadriatic Lineament References: Bossew Peter. Mapping the Geogenic Radon Potential and Estimation of Radon Prone Areas in Germany. Radiation Emergency Medicine 2015 Vol. 4, No.2 13-20. Council Directive 2013/59/EURATOM. Basic safety standards for protection against the dangers arising from exposure to ionising radiation. Minach L., Verdi L., Marchesoni C., Amadori C. Radon in Südtirol. Environmental Protection Agency. 1999. WHO 2009. Zeeb H. and Shannoun F. (eds.) WHO handbook in Indoor Radon - a public health perspective. ISBN 978 92 4 1547672.