Soil health assessment and ecological risks associated with a tungsten-rich Scheelite mining site in a Brazilian semiarid region

Mining activities can severely impact soil health and ecosystem balance, particularly through metal contamination. This study investigated the effects of metals on microbial and enzymatic activity, alongside ecological risks in tungsten-rich Scheelite mining areas in semiarid Brazil. Three land use systems were selected, representing tailings (~ 30 years deposited), degraded (vegetation removal and machinery impact), and native vegetation (reference). Soil contamination by tungsten (W) and other metals, ecological risk indices, microbial properties, enzymatic activity, and stoichiometry were assessed. Higher concentrations of W, Cd, Mo, and Pb were found in tailings, whereas Cr and Zn were more abundant in degraded soils compared to the native system. Although most Cu, Cd, and Pb concentrations were within or close to the ranges commonly reported for non-polluted soils, the geoaccumulation and ecological risk indices indicated moderate to high potential environmental risks, mainly associated with W and Cd, particularly in tailings. Soil respiration and microbial biomass carbon were reduced by up to 51.82% and 79.65%, respectively, in tailings compared to native vegetation. Enzymatic activities of β-glucosidase, urease, arylsulfatase, and alkaline phosphatase declined by 82.8%, 69.2%, 93.5%, and 62%, respectively, in tailings, and by 27.9%, 59.6%, 59.5%, and 28% in degraded soils, while acid phosphatase activity increased by 276.6% in degraded sites compared to tailings. C: N and C: P ratios decreased under tailings, whereas N: P ratios increased. Our findings highlight mining's impact on soil health due to W contamination and offer new insights for managing ecology in these areas.