Fractionations of heavy metals and their correlations with magnetic susceptibility in soil from a typical alluvial island in the lower yangtze river, China

The use of magnetic susceptibility (χ) as a means of assessing heavy metal pollution in soils has been explored by researchers, yielding varying results in terms of the correlations between χ with heavy metals. The efficacy of χ as an indicator of soil heavy metal pollution remains a topic of debate. This study aims to elucidate the inter-relationships between χ, iron oxides, and heavy metals in soil through the application of a modified 5-step sequential extraction procedure (SEP), and to identify an effective approach for assessing metal concentrations in soil using magnetic susceptibility measurements. The soil samples were collected from a typical alluvial island in the lower Yangtze River, China, and a total of 6 forms (exchangeable and acid soluble fraction, easily reducible fraction, oxidizable fraction, amorphous iron oxide, crystallized iron oxyhydroxides and residual fraction) were partitioned and their heavy metal concentrations and χ were analyzed. The results show that crystalline Fe oxyhydroxides and residual fractions are the two uppermost fractions of heavy metals. By combining the fractionation of elements with the variation of χ of the soil during the processing of SEP, it was inferred that the external input of Fe, Pb, Cr and Cd in the soil likely originated from the vicinal steel production. The correlation analysis revealed a significant correlation between heavy metal concentrations and χ in the residual fraction, whereas no significant correlations were observed between the concentrations of heavy metals and χ in the bulk soil samples. It is recommended that the evaluation of heavy metal contamination in the soil neighboring industrial sites can be conducted via magnetic susceptibility measurements subsequent to the elimination of crystalline iron oxyhydroxides.