EDTA facilitated phytoextraction of Pb, Cd and Zn from a lead – zinc mine contaminated soil by three new accumulator plants (Marrubium cuneatum, Stipa arabica and Verbascum speciosum)

Abstract

This study aims to evaluate the enhancement of phytoextraction of heavy metals Pb, Cd and Zn by species M. cuneatum, S. arabica and V. speciosum, through EDTA amendment. Assisted phytoextraction pot experiments were performed at different EDTA dosages (0, 1, 3 and 5 mmol kg-1 soil). Generally, applying EDTA decreased pH and increased EC, while no significant effect was observed on organic matter, nitrogen, and exchangeable K and P. Also the activity of soil dehydrogenase enzyme was inhibited at 5 mmol kg-1 EDTA. The phytoavailability of Cd, Pb and Zn increased significantly in the presence of EDTA, followed by the contents of them in the tissues of all three studied species amplified. Resulting from oxidative stress caused by the accumulation of metals, the activity of antioxidant enzymes such as, glutathione peroxidase (GPX), superoxide dismutase (SOD) and catalase (CAT) increased, when chelating agent was added. EDTA showed fluctuating effect on malondialdehyde (MDA) content and in higher doses it partially decreased chlorophyll concentration. EDTA at the level of 1 and 3 mmol kg-1 enhanced the plant growth, but 5 mmol kg-1 of that reduced the biomass of the studied species. The Bioconcentration factor (BCF) for Cd was notably high in all studied plants, and considerably elevated for Zn and Pb with the addition of EDTA in M. cuneatum and S. arabica (BCF>1), whilst accumulation factor greater one (AF>1) were found for Cd in all species and for Pb in the case of S. arabica. Predictive models for metal accumulation in plant tissues were developed using stepwise multiple linear regression, with pH and Cd showing the highest contribution to interpretation and variability of the dependent variables. In general, the results demonstrated that EDTA can be an effective amendment for phytoextraction of Cd, Zn and Pb by M. cuneatum, V. speciosum and S. arabica in contaminated soils.