Abstract

Soil contamination by heavy metals is widely spread and concerns have been raised over the potential risks to humans, animals and agricultural crops. Toxic metals are readily accumulated in some plants and may cause a threat to humans and grazing animals. In this study, an assessment on contaminated edible vegetables by heavy metals is made. Two major sites (denoted S1 and S2) where durum wheat (Triticum durum Desf.) and pepper (Capsicum annuum) are widely cultivated in Algeria have been considered. S1 and S2 have been subjected to chemical characterisation, total metal quantification (Cd, Cu, Zn, Pb, Ni and Co) and sequential extraction as well metal speciation. Total content of the metals in the soils were found to be below the internationally recommended and permissible limits set for agricultural use for all the heavy metals except for Pb (mostly bound to iron and manganese oxides) in S2. Whereas Cd and Zn concentrations were higher in both S1 and S2; Cd, Cu, Zn, Ni and Co were mainly present in residual form, appearing less bio-available. As a consequence, these soils exhibit significant contamination. In the edible portions of durum wheat and pepper, the respective concentrations of Cd and Cu as well as of Pb, Zn, and Ni are found to exceed the permitted limits of the European Standards. The study indicates a potential ecological risk of the contaminated plants by most heavy metals except in the case of Co, causing potential health risk.

Key words: Heavy metals, soil, contamination, sequential extraction.