Evaluation of potentially toxic elements' (PTEs) vertical distribution in sediments of Gafsa-Metlaoui mining basin (Southwestern Tunisia) using geochemical and multivariate statistical analysis approaches

The present study represents a preliminary geochemical investigation concerning the vertical distribution of potentially toxic elements (PTEs) in the sediments of an industrial site in Gafsa-Metlaoui mining basin of phosphate using multivariate statistical analysis. It attempts to outline the possible source of the PTEs and their relation with soil texture, soil profile and human activities. Consequently, 14 sub-samples were collected from a sediment core of 30cm depth. The PTEs ranged as follows: Zn>Cd>Cr>Pb with mean concentrations of 194.5, 26.92, 13.42 and 8.07mgkg(-1), respectively. Pearson's correlation matrix showed positive correlations between Zn, Cd, P2O5, CaO, SiO2 and total organic carbon except for Pb and Cr, which seem to be interrelated, although they correlated negatively with all parameters. The principal component analysis (PCA) extracted three principal components representing 87.25% of the total variance. Similarly, hierarchical cluster analysis (HCA) confirmed the results obtained by the PCA, classifying the analyzed parameters into three different groups. The obtained data imply that PTEs concentrations in the study area are influenced by various factors such as anthropogenic and lithogenic sources. Zn, Cd, P2O5, CaO, SiO2 and organic matter (OM) probably have the same anthropogenic origin related to the phosphate industry, while Cr and Pb share the same natural source. The sediment contamination assessment proved that the samples of the study area are heavily polluted with Cd, moderately to heavily polluted with Zn and not polluted with Cr and Pb.