Fractionation of metals in cadmium contaminated soil: Relation and effect on bioavailable cadmium

The effect of five metals (Cu, Fe, Mn, Pb and Zn) and soil pH, organic matter (OM) and oxidation–reduction potential (ORP) on bioavailable Cd in contaminated areas downstream of the Padaeng Zn mine in Mae Sot, Tak Province, Thailand was investigated. Soil samples were collected to characterize the bioavailable fractions of Cd, Cu, Fe, Mn, Pb and Zn by comparing weakly bound fractions with total metal concentrations using ICP-OES Spectroscopy. Acid digestion (US EPA, Method 3052) and the first two steps of the BCR sequential extraction method proposed by the Standards, Measurements and Testing Programme (SM&M) were adopted for the determination of total metals and bioavailable metals, respectively. Studied soil samples showed a wide range of physicochemical properties: pH (5.79 to 8.07); OM (0.52 to 4.16 g kg− 1 soil); ORP (− 291.1 to 347.9 mV). Of the elements studied, Cd has the highest mobility since it presents the highest content in the first fraction BCR1 (exchangeable fraction) followed by Mn, Zn, Pb, Cu and Fe, respectively. Principal Component Analysis (PCA) together with correlation analysis showed supporting results, implying that some interactions and/or relations existed among these metals (Cd, Pb and Zn) in both bioavailable and total forms. Spearman correlation coefficients (r) all showed significant positive correlations: bioavailable Cd–bioavailable Pb; bioavailable Cd–bioavailable Zn; bioavailable Cd–total Cd; bioavailable Cd–total Pb, and bioavailable Cd–total Zn (r = 0.296*, 0.946*, 0.554*, 0.321*, and 0.468*, respectively).