Origin of radioactivity in a neoformed mineral: the case of epsomite from the Perticara sulfur mine

Abstract

Recently, high amounts of toxic and radioactive elements have been discovered in epsomite crystals in the abandoned sulphur mine of Perticara, Italy (Giordani et al., 2022). Epsomite represents a neoformed mineral grown in the galleries after the extraction activities of the sulfur mine. In particular, a content of 5.59 ± 0.84 Bq/g of 210Po was detected in the epsomite phase, coupled with other toxic elements such as 228Th, As, Co, Fe, Mn, Ni, Sr, Ti, Zn. The anomalous content of polonium led to new investigations of the area through the study of different matrices present in the galleries: minerals, host-rock, water, air, dust and bitumen, with the aim to define the origin and the distribution of this hazardous element. The samples were investigated combining several analytical techniques: X-ray Powder Diffraction (XRPD), Environmental Scanning Electron Microscopy (ESEM-EDS), Inductively Coupled Plasma-Atomic Emission (ICP-AES), Inductively Coupled Plasma-Mass Spectrometry (ICP-MS), Atomic Absorption Spectrometry (AAS), Gamma Spectrometry, Alpha Spectrometry, Radon Monitor, and Alpha Track Detector (ATD). Water samples showed high Al, Fe, Pb, Mg, and Mn content but not radioactive elements. The bitumen sample showed a higher amount of 210Po and 210Pb (0.12 ± 0.02 Bq/g and 0.11 ± 0.02 Bq/g, respectively), compared to the host-rock and fibrous sericolite samples, but lower than fibrous epsomite crystals (210Po 5.59 ± 0.84 Bq/g; 210Pb 5.93 ± 1.19 Bq/g). A slight anomaly in the 40K and 226Ra content of the host-rock was observed (0.38 ± 0.05 Bq/g and 0.052 ± 0.007 Bq/g respectively), and a high 222Rn concentration (up to 2200 ± 300 Bq/m3) was also detected in the tunnels (Giordani et al., 2024). The confined atmosphere of the mine, with the high 222Rn concentration, is likely the source of the high level of 210Po and 210Pb, in radioactive equilibrium, detected in epsomite. Thus, the 222Rn-rich, anoxic, and hypoxic atmosphere, coupled with the abundance of Mn, Fe, and organic matter in the mine, could play a key role in the 210Po remobilization. This work highlighted that natural epsomite, which is a very common mineral phase in mines, caves, and underground environments, is able to capture 210Po and 210Pb. For this reason, it should be used as a mineral indicator for the presence of radioactive elements in similar environmental conditions, also helping to ensure safe management. These results indicate that in areas with a long history of mining, despite decommissioning, environmental hazards and human health risks may still emerge in terms of radioactivity and potentially toxic elements (PTEs).   Giordani, M., Meli, M.A., Roselli, C., Betti, M., Peruzzi, F., Taussi, M., Valentini, L., Fagiolino, I. and Mattioli, M., 2022. Could soluble minerals be hazardous to human health? Evidence from fibrous epsomite. Environmental Research, 206, p.112579. Giordani, M., Taussi, M., Meli, M.A., Roselli, C., Zambelli, G., Fagiolino, I. and Mattioli, M., 2024. High-levels of toxic elements and radioactivity in an abandoned sulphur mine: Insights on the origin and associated environmental concerns. Science of the Total Environment, 906, p.167498.