Study regionItaly.Study focusThe oxygen isotope composition from 266 pluviometers was used to study the spatial variability of δ18O and its relationship with Italian orography. The local meteoric water lines (LMWLs) of northern, southern and central Italy and Sicily are reformulated and a new definition of isotopic variations with elevation is provided.New hydrological insights for the regionAltitude and, to a lesser extent, latitude are the main geographical factors affecting the isotopic signature of precipitation in Italy. A high-resolution map of the spatial distribution of 18O content in precipitation was created using the identified relationship between δ18O/Latitude-Altitude and the spatial distribution of the residuals. The general features of the δ18O distribution map may be summarised as follows: δ18O distribution over the Alps clearly depends on latitude and altitude, whereas over the Apennines, which run down the whole peninsula from north-west to south-east, it is more affected by altitude, the contour lines roughly following the axis of the chain. The isotope compositions on the western side of the peninsula are generally higher than those of the east at the same elevation and latitude; they are more or less uniform in the northern plain of Italy

Radon (²²²Rn) is a natural radioactive gas formed in rocks and soil by the decay of its parent nuclide (238-Uranium). The rate at which radon migrates to the surface, be it along faults or directly emanated from shallow soil, represents the Geogenic Radon Potential (GRP) of an area. Considering that the GRP is often linked to indoor radon risk levels, we have conducted multi-disciplinary research to: (i) define local GRPs and investigate their relationship with associated indoor Rn levels; (ii) evaluate inhaled radiation dosages and the associated risk to the inhabitants; and (iii) define radon priority areas (RPAs) as required by the Directive 2013/59/Euratom. In the framework of the EU-funded LIFE-Respire project, a large amount of data (radionuclide content, soil gas samples, terrestrial gamma, indoor radon) was collected from three municipalities located in different volcanic districts of the Lazio region (central Italy) that are characterised by low to high GRP. Results highlight the positive correlation between the radionuclide content of the outcropping rocks, the soil Rn concentrations and the presence of high indoor Rn values in areas with medium to high GRP. Data confirm that the Cimini–Vicani area has inhalation dosages that are higher than the reference value of 10 mSv/y.