Single and combined effect of chelating, reductive agents, and agro-industrial by-product treatments on As, Pb, and Zn mobility in a mine-affected soil over time

Application of chelating and reductive agents in soils can increase the availability of potentially toxic elements facilitating their uptake by plants. This study discusses the effect of single or combined EDTA (E), sodium dithionite (SD), and olive mill wastewater (OMW) treatments on As, Pb, and Zn mobility over time in a heavily contaminated mine-affected soil. Soil samples were incubated for 1, 3, 7, 15, 30, 60, and 90 days and at each incubation time the easily mobilizable fraction obtained by (NH₄)₂SO₄ (for As) and CH₃COOH (for Pb/Zn). The results showed that the highest availability of As (mean value 41 mg kg^-1) was observed for the EDTA treatment followed by E+OMW (mean value 32 mg kg^-1) and E+SD+OMW (mean value 27 mg kg^-1). For Pb and Zn, significantly higher available concentrations were obtained by the EDTA and E+OMW treatments (mean values 2532 mg kg^-1 and 1427 mg kg^-1 for Pb and Zn respectively) followed by the E+SD (mean value 2259 and 1333 mg kg^-1 for Pb and Zn) and E+SD+OMW treatments (mean value 2388 and 1340 mg kg^-1 for Pb and Zn). Moreover, the incubated for 90 days soil samples subjected to two different sequential extraction protocols (SEPs): Wenzel (for As) and BCR (for Pb, Zn, Fe, and Mn). The results showed that As, Pb, and Zn mobility was mainly regulated by the amorphous Fe oxides. Our findings suggest that OMW application in soils should focus more attention since when combined with other amendments produced contradictory results.