Phytormediation of metal-contaminated soils and sediments by hemp and giant reed as implemented by selected bacteria and chelating agents

The present study was carried out to assess the effects of EDTA and selected bacteria on the phytoremediation of soils and sediments historically contaminated by Cu, Cr and Ni. A total of 42 bacterial strains resistant to these three metals were isolated and screened for plant growth promoting traits and metals bioaccumulation, resulting in two selected Enterobacter spp. strains. Phytoremediation pot experiments of 3 months duration were carried out with hemp (Cannabis sativa L.) and giant reed (Arundo donax L.) grown on soils and sediments respectively: in both cases the effects of inocula with the selected bacteria and addition of EDTA were compared. Microbial inocula significantly increased leaf and stem biomass in giant reed, while in hemp no differences were detected. Plant physiological parameters were not significantly different between plants grown on contaminated and non-contaminated soils or sediments. Leaf area in inoculated pots was also significantly higher than in controls for both plants. In hemp, bioaccumulation followed the order Ni>Cu>Cr, with higher accumulation in roots than in stems, flowers and leaves. EDTA addition significantlyincreased above biomass accumulation of Ni and Cu . In hemp addition of the microbial inoculum did not affect remediationpotential; removal percentages were below 0.5% for all three metals. In giant reed the highest accumulation were found in below-ground biomass (rhizomes and roots). Removal of metals by rhizomes and roots was significantly increased with EDTA or microbial inoculum. Leaching of metals with irrigation water was was greatly enhanced with the addition of EDTA. The higest removal of metals, up to 7%, were obtained with giant reed combined with chemical leaching. This approach could be used to lower the heavy metal concentration of the target site to the levels required for public use in less than 5 years.