Cadmium, lead and arsenic contamination in an abandoned nonferrous metal smelting site in southern China: Chemical speciation and mobility

The investigation of chemical speciation of primary toxic metal(loid)s (Cd, Pb, and As) in soil profile in nonferrous metal smelting site is a key to the assessment of their mobility characteristics and formulation of subsequent remediation strategy. In this study, 74 soil samples were collected at 12 different soil profiles; soil physio-chemical properties and total content of Cd, Pb and As and corresponding chemical speciation were also determined. The results showed that the mean total concentration followed the order of Pb 3 m). Heavy pollution of Pb, Cd and As were observed in the whole soil profile at the area of fuel oil storage tank (ZY6) and lead smelting area (ZY8). The dominant fraction of Cd was exchangeable fraction (F1); Pb was dominant in Fe/Mn oxides-bound fraction (F3) in most cases; Crystallized Fe/Al hydrous oxides bound fraction (F4) generally accounted for a large proportion of As. Mobility factor (MF) followed the order Cd As > Pb, indicating that Cd was the most mobile element in soil profiles. Pearson correlation analysis found that MFCd was significantly positively correlated to soil silt; the F4 fraction percentage of As was significantly positively correlated to soil redox potential (Eh). Additionally, MFCd/Pb was found to be positively correlated to crystalline iron (Fec), while negatively correlated to amorphous iron (Feo). The findings reported in this study, on the basis of distribution characteristics of chemical speciation could provide a new solution for future soil remediation at the site. Long-term solutions to metal(loid)s pollution might be offered by microbial-assisted soil washing technique that promotes the transformation of Fe/Mn oxides-bound fraction and organic/sulfide-bound fraction.

Automated summary

Investigating the chemical speciation of toxic metals (Cd, Pb, and As) in soil profiles is crucial for assessing their mobility and formulating effective remediation strategies. This study examined 74 soil samples from 12 different profiles and found that Pb, Cd, and As were heavily polluted in certain areas. The dominant fraction of Cd was exchangeable, Pb was mainly bound to Fe/Mn oxides, and a large proportion of As was associated with crystallized Fe/Al hydrous oxides. Cd showed the highest mobility, and its mobility was positively correlated with soil silt content. The results highlight the importance of considering chemical speciation in future soil remediation efforts.