Assessment of danger of polymetallic contamination of mountainous meadow soils from the tailing of the Urup Mining and Processing Plant, 20 February 2025

The Urupsky Mining and Processing Plant (UMPP) is the largest enterprise in the south of European Russia for the extraction and processing of copper pyrite, the waste of which contains high concentrations of heavy metals. Their migration results in pollution of soil adjacent to the existing tailing. We have estimated the degree of contamination of the upper 10-cm-thick layer of mountainous meadow chernozem like soil (Mollic Leptosol) with 48 potentially toxic elements (PTEs) depending on the distance from the tailing and the impact of pollution on the biological properties of soil. At a distance of 5 m from the tailing, the list of priority pollutants includes Ag (its content exceeds the background value by 63 times), Sb (25); Hg (23),Cu (19), Te (19), Zn (14), Cd (14), As (13), Mo (12), Pb (6), Sn (3.7), and Bi (3.6). At the same time, at 300–400 m from the tailings dump, soil pollution is no longer observed. The degree of soil pollution generally correlates with the studied indicators of the biological activity of soils. The biological properties of the soils improve with a distance from the tailing. Thus, the catalase and dehydrogenase activity, the total number of bacteria, and the length of roots of reddish seedlings are restored to normal values at a distance of 100 m from the tailing; the activity of urease, germination capacity, growth rate, and the length of reddish shoots, at a distance of 200 m; the activity of invertase, at a distance of 300 m; and the abundance of bacteria of the genus Azotobacter, at a distance of 400 m. Thus, the abundance of Azotobacter bacteria, and the is the dehydrogenase and invertase activities are the most sensitive indicators of the polymetallic contamination of the mountainous meadow chernozemlike soil from the UMPP tailing; the activities of dehydrogenases, catalase, and invertase display the strongest correlation with the contents of studied PTEs in the soils.