Potentially toxic elements and radionuclides contamination in soils from the vicinity of an ancient mercury mine in Huancavelica, Peru

Abstract

Mining activities can release large amounts of potentially toxic elements (PTE) and radionuclides in an uncontrolled manner, causing environmental contamination. This work looks at the PTE and radionuclide levels in Huancavelica, a Peruvian Andean city where the ancient mercury mine Santa Barbara operated for about five centuries, from 1573 to 1970. Although the mine closed in 1970, reports indicate that PTE contamination persists. Five representative soil samples were collected from the north, south, east and west sides of the city near the Huancavelica River. The samples were analyzed by X-ray fluorescence spectroscopy (XRF), Inductively Coupled Plasma – Mass Spectroscopy (ICP-MS) and Gamma Spectroscopy. High contamination levels of As, Cd, Pb, Zn, Ni and Cu, while low levels of Hg and Cr were found compared to the local and international standards. The highest concentration Ni (184.3 mg kg–1), Cu (1223 mg kg–1), Zn (1526 mg kg–1), Cd (11.41 mg kg–1) and Hg (6.2 mg kg–1) were found in Yananaco, the district closest to the mine. This area also showed the presence of calcite. In addition, the specific activities of the three naturally occurring radioactive materials (NORM) varied: 226Ra from 38.0 to 137.3 Bq kg–1232Th from 40.1 to 50.5 Bq kg–1, and 40K from 505.5 to 793.3 Bq kg–1. The average absorbed dose rate (D) for the samples was 85.9 nGy/h, which is 1.7 times higher than the global average. Similarly, the average Annual Effective Dose (E) was 0.105 mSv/y, 1.5 times higher than the world average. Furthermore, the data reveal strong positive Pearson correlations for Hg-Ni pairs (0.981) and 226Ra-232Th (0.960). Negative correlations were found for 226Ra-As pairs (–0.984) and 232Th-As (-0.962). These results indicate that historical mercury extraction activities increased exposure of PTE and NORM in Huancavelica. This contamination remains in areas near the abandoned mine today.