The impact of lead-zinc mining activities on watershed environment with respect to lead (Pb) isotopes: A case study in typical mining areas of the western Qinling Mountains, China

Gaining insight into the environmental effects of industrial and mining activities is an important prerequisite for regional eco-environment protection and governance. Hence, in this study, three types of samples (tailings, deep soils, and river sediments) were systematically collected from typical lead-zinc mining areas in the western Qinling Mountains of central China. An exhaustive study on the impact of lead-zinc mining activities on a watershed environment was conducted using elemental and isotopic geochemistry of Pb. The results indicated that the Pb content was significantly enriched in sediments, with a mean value of 58.99 mg/kg significantly higher (2.2 times the regional background and 2.6 times the national level; p = 0.001). Spatially widespread Pb pollution was observed, ranging from mild to moderate levels based on geo-accumulation index (I_geo) values. The spatial distribution of Pb content and the pollution status in sediments maintained a high degree of consistency, with concentrations being low in the northwest and high in the southeast. By utilizing Pb isotopic fingerprinting technology (²⁰⁸Pb/²⁰⁶Pb-²⁰⁶Pb/²⁰⁷Pb), this study successfully designed a binary mixed model for the Pb sources in sediments, including the anthropogenic source represented by lead-zinc tailings (with the mean ²⁰⁶Pb/²⁰⁷Pb value of 1.1534 and the mean ²⁰⁸Pb/²⁰⁶Pb value of 2.1193) and the natural source reflected by deep soil (with the mean ²⁰⁶Pb/²⁰⁷Pb value of 1.1936 and the mean ²⁰⁸Pb/²⁰⁶Pb value of 2.0822). Through quantitative source apportionment, anthropogenic Pb contributed approximately half (49.70% ±5%) of the total Pb in sediments. Notably, in areas with concentrated lead-zinc mining activities, the anthropogenic contribution reached 84.06% ±5%. The above revealed that lead-zinc mining activities were the main contributor of Pb and that these activities lead to a significant transformation in the geochemical field. Moreover, by blending the natural geological background and the comprehensive characteristics of Pb geochemistry, three geochemical zones were determined to facilitate the scientific management and protection of regional environment.