Effect of biodegradable chelating agents on heavy metals phytoextraction with Mirabilis jalapa and on its associated bacteria

The application of chelating agents can be associated with phytoremediation in order to reduce the time required for remediation of heavy metal contaminated soils. The present work has the purpose to test the use of easily biodegradable chelating agents in the assisted phytoextraction process and to evaluate their effect on soil and Mirabilis jalapa plant associated bacteria. Two easily biodegradable chelating agents were used (EDDS and MGDA) in two different dosages (4 and 8 mmol/kg of soil). Metal concentration in soil solution, in leaves and in leachate were determined during the phytoextraction process, while at the end of the experiment metal concentration was evaluated separately in roots, stalk and leaves. In untreated reactors Zn and Pb were accumulated in the roots, but only Zn was translocated to the shoots. Both chelating agents demonstrated to be very effective in Pb and Zn mobilization in soil solution. After chelate treatment, accumulation and translocation of the two metals was different: unaffected with regard to Zn and enhanced with regard to Pb. The chelating agents seem to have a positive influence on bacterial communities of bulk soil and rhizosphere by mitigating the selective pressure caused by Pb and Zn, whereas the endophytes are less affected.