First radon dataset from the seismic area of north-eastern Sicily, Italy

North-eastern Sicily can be considered a radon-prone area due to the presence of a Variscan crystalline basement, that includes high-radionuclides content rocks such as low to high-grade metamorphites and felsic plutonic rocks. The area is also characterized by intense seismic activity: the Mw 7.1 seismic event that struck this area on 28^th December 1908 is still the deadliest earthquake recorded in Europe, having caused more than 120,000 casualties. Despite the proven link between high radon concentrations and some geogenic and tectonic settings (e.g. seismogenic areas and volcanic and crystalline rock environments), no radiological data had been collected for north-eastern Sicily. In order to fill this gap, a series of radiological surveys were performed in a sector of this vulnerable area with the aim of determining the radon concentration in soil gases and groundwaters.

Radon dissolved in groundwater was derived in the range of 1.6–57.5 Bq L^-1, well below the limit of 100 Bq L^-1 set by the Italian Legislation (D. Lgs. 28/2016). Concerning soil gases, radon and thoron levels range from <1 to 81 kBq m^-3 and from 3 to 123 kBq m^-3, respectively. All those values are quite similar to those recorded in the adjacent Region of Calabria by previous studies.

Although the health risk due to ingestion and inhalation of groundwater can be neglected, the presence of several soil radon anomalies testifies a potentially harmful effect on the population. Radon index maps, built based on the measured radon concentration and the permeability of the soil, highlight that parts of the investigated area are characterized by an enhanced hazard. Those maps might have a useful role in preliminary screening activities related to the identification of the so-called Radon Priority Areas (EURATOM 59/2013 and Italian legislative decree 101/2020).

Soil-radon anomalous values seem to have a tectonic origin and are presumably associated with the presence of fault segments probably representing the on-land continuation of a transtensional fault zone located in the southern Tyrrhenian Sea between the Aeolian Island and the northern margin of Sicily. In this context, the seismic and radiological hazards are strictly connected, further complicating the mitigation strategies against those geological processes. Since this study illustrates the first radiological data collected in this sector of the southern Apennines of Italy, a lot of work has to be done in the near future. The main goals are to extend radon investigation in other sectors of north-eastern Sicily as well as to perform a series of indoor radon measurements to determine if a clear correlation exists between high soil radon areas and high indoor radon levels.