Evaluation and Origin Studies of Heavy Metals in Soils Around Traditional Mining Regions in the Northwest Guizhou District

Abstract

Heavy metal contamination in soil has emerged as a critical environmental issue. However, research specifically addressing the distribution, pollution levels, and source analysis of heavy metals in lead-zinc mining areas remains limited. To assess the extent of soil heavy metal pollution around a lead-zinc mine in northwest Guizhou and to perform a quantitative source analysis, this study collected 56 surface soil samples and 14 samples from two different depths. The concentrations and chemical forms of Cd, Pb, Cr, Cu, Ni, and Zn were measured. Pollution levels were evaluated using the geoaccumulation index (Igeo) and the secondary-to-primary phase ratio (RSP). Sources were identified through correlation analysis, principal component analysis, and positive matrix factorization (PMF). The results demonstrated that: (1) The average concentrations of Pb, Zn, Cd, Cr, Cu, and Ni were all below Guizhou’s soil background levels. While Cd and Pb reached maximum values close to background levels, their coefficients of variation were 66.56%, 413.84%, 123.04%, 195.69%, 319.98%, and 373.41%, respectively, indicating high variability and significant anthropogenic influence. Elevated levels of Cd, Cu, Pb, and Zn are closely aligned with mining locations. (2) The Igeo evaluations indicated that most areas were unpolluted; however, the RSP method revealed that 5% and 4% of sites were slightly polluted by Pb and Zn, respectively, with 4% showing slight Cd contamination, and 2% experiencing moderate to severe pollution. (3) PMF source apportionment identified five main sources: 63.7% of Cr from agriculture, 72.3% of Cd from atmospheric deposition, 59.1% of Zn and 41.9% of Ni from wastewater discharge, 52.9% of Cu, 45.4% of Ni, and 36.2% of Cr from traffic emissions, and 79.9% of Pb from mining activities. The study concluded that overall heavy metal pollution was slight, though Cd, Pb, and Zn were notably influenced by mining and associated human activities. Different sources contributed distinctly: mining primarily impacted Pb, while agriculture, atmospheric deposition, and wastewater discharge mainly affected Cr, Cd, and Zn accumulation, respectively. These findings offer a scientific basis for soil pollution prevention, control, and ecological risk management in the region.