Enrichment and Source Apportionment of Heavy Metals in Selenium-Enriched Soils in Eastern China

Selenium (Se)-enriched soils in southern Anhui Province, eastern China, exhibit significantly elevated geochemical backgrounds of heavy metals (HMs). However, the enrichment characteristics and sources of these HMs require further elucidation. This study conducted comprehensive geochemical analyses on soils and underlying bedrocks to investigate the enrichment and sources of eight HMs including As, Cd, Cr, Cu, Mo, Pb, Zn, and Ni. The concentrations of HMs in Se-enriched soils generally exceed regional background values and even surpass risk screening thresholds in China, particularly for As, Cd, and Mo. Sequential extraction analysis reveals that As, Pb, and Cr in Se-enriched soils are predominantly associated with the residual fraction (>50%). In contrast, Cd is characterized by high bioavailability, with 29.85% found in the exchangeable fraction and 14.01% in the carbonates fraction. Pb isotope tracing indicates that the sources of Pb in soils derive from the weathering of underlying bedrocks (34.59%), coal combustion (34.21%), and vehicle exhaust (31.20%). Using the positive matrix factorization (PMF) model, four primary sources of HMs in these soils were identified: (1) mining and smelting activities associated with coal combustion (Cd, Cr, Zn); (2) weathering of the underlying bedrocks; (3) leaching from Mo-rich ores in bedrocks; and (4) traffic emissions and agricultural inputs. These findings establish a scientific basis for the effective utilization and management of Se-enriched soils.