The influence of geogenic and anthropogenic factors on indoor radon exposure in the Ervedosa ore district (Vinhais - Northeastern Portugal)

The Ervedosa ore district lies in the Galiza and Trás-os-Montes Zone. The schist S1 is dominated by low-grade metamorphism, and schist S2 occurs along or close to the uranium mineralized area with secondary minerals along the schistosity plane. These metamorphic rocks are intruded by a syn-tectonic Variscan granite pluton with an elongated form, constrained by the NW-SE Rebordelo (RE) ductile shear zone. Geochemical and radiological data obtained in the three localities of the Ervedosa village suggest that the radon concentrations in dwellings are mainly related to the uranium content of rocks and their mobilization through weathering processes, but human habits also have a role on it. The Ervedosa Mine (EM) granite, presents the highest average of uranium concentration (14 ppm). The results of the gamma dose rate are related to the uranium contents of the rocks and weathering processes. Thus, radon risk exposure is moderate to high in dwellings located in EM granite and schist S2, and low for RE granite and schist S1. Overall, radon concentrations determined in 46 dwellings during winter conditions shown a geometric mean of 257.1 Bq·m^-3. Therefore 32% of measurements exceeded the 300 Bq.m^-3 reference limit, by the DL n.^o108/2018. The present study alert for human health risks from indoor radon exposure and also recommend preventive and corrective measures in this region. Awareness campaigns for public should also be improved to ensure natural ventilation in dwellings during the winter period and reduce the indoor radon exposure.