Spatial distribution and source identification of heavy metals in a typical Pb/Zn smelter in an arid area of northwest China

Heavy-metal pollution has become a serious problem in the vicinity of mining sites. In this study, we investigated the pollution degree and spatial distribution of heavy metals and determined their sources in soil near a typical Pb/Zn smelter in an arid area of northwest China. The pollution degree, spatial distribution and source identification of heavy metals were evaluated and analyzed by the geo-accumulation index (I-geo), enrichment factor (EF), ArcGIS-based kriging interpolation models and multivariate statistical techniques. The results showed that the average concentrations of Pb, Zn, Cd and Cu were higher than their background contents of Shaanxi Province. The results of chemical speciation fractions show that the non-residual fraction (Acid soluble + Reducible + Oxidizable) of Pb, Zn and Cd were greater than the residual fractions of the same elements, while the results of Cr, Cu and Mn were just contrary. The I-geo values demonstrated that the issue of soils contaminated by Pb, Zn and Cd in this area is very serious, where Cd pollution was the most significant. The EF values decrease in the following order: Cd > Zn > Pb > Cu > Cr, and indicating Cd was extremely severe enrichment. The spatial distribution indicated that Pb, Zn, Cd and Cu mainly originated from smelting activities, which were heavily accumulated in topsoils and decreased with increasing soil depth in the profile distribution. The indexes of I-geo and EF showed that Pb, Zn, Cd and Cu were the most important contaminants, which had the same sources, deriving from anthropogenic metal smelting activities. These results can serve as a basis for designing effective strategies to prevent, control and reduce further heavy-metal contamination of the soils. Meanwhile, the relevant study methods, study hypotheses and methodologies may provide certain reference significance for the study of soil pollution from similar heavy metals.