Assessment of metal accumulation in calcareous soil and forage crops subjected to long-term irrigation using treated wastewater: Case of El Hajeb-Sfax, Tunisia

In Sfax (Tunisia), waters deriving from the treatment of a mix of industrial and domestic effluents have been used for the purpose of forage crop irrigation for 17 years. The aim of this study is to evaluate the impact of this wastewater irrigation on the metal contents in soil and to assess the risk of metal uptake by plants over the long term. The bioavailability and phytoabsorption of metals by alfalfa (Medicago sativa) and sorghum (Sorghum bicolor) forage crops have been evaluated through an approach based on spatially distributed topsoil (0–7 cm) and plant samples. This approach uses direct measurements of the metal uptake by the roots and shoot tissues of the plants, in addition to the total metal content of the soil and the available fraction for uptake by plants (i.e. the bioavailable fraction), as extracted by ethylenediaminetetra-acetic acid (EDTA) mixed with ammonium acetate (NH4OAc). Two sites were selected from within the same calcisol field so as to focus on various agricultural practices.