Heavy metal pollution and source analysis of soils around abandoned Pb/Zn smelting sites: Environmental risks and fractionation analysis

Abstract

We used granulometric techniques, wet sieve analysis and Tessier sequential extraction to analyze heavy metal (HM) contamination in soils from abandoned Pb/Zn smelting sites in Zhuzhou, China. The soil pH values varied between 6.47 and 8.50 (mean 8.02), which controls the mobility of HMs, and total organic carbon (TOC) levels averaged 3.48 g/kg. Sequential extraction reveals that the majority of HMs are present in the residual, Fe-Mn oxide, and organic bound fractions, with the exception of Cd and As with high bioavailability Cd (0.81–4.07 mg/kg) and As (70.18–295.90 mg/kg). Zn occurs predominantly in residual and Fe-Mn phases, while Cd exists primarily as the exchangeable fraction, both of which can cause an environmental risk. The positive relationship between finer particle size and HM content demonstrates that soil texture plays a significant role in HM retention and mobility. Pollution indices (I-geo, PI, and NPI) indicate high to extremely high Cd concentrations, as well as As risk, with a substantial ecological risk index (RI) surpassing safety thresholds. The positive matrix factorization (PMF) and principal component analysis (PCA) reveal industrial emissions, atmospheric deposition, and soil parent materials to be prominent sources of contamination. These findings highlight the necessity for specific remediation actions, especially concerning Cd and As to diminish ecological risks and potential human health threats while stressing the need for ongoing monitoring and sustainable management in the affected areas from historical smelting activities.