Phytoremediation Potential of Thistle (Cynara Cardunculus L.) and its Ability to Remove Heavy Metals from Polluted Soils with High Rates of Sewage Sludge

This work studied the use of thistle (Cynara cardunculus L) in order to phytoextract heavy metals from polluted soils due to the application of high rates of thermally dried sewage sludge (TDS). Total and available heavy metals content (Pb, Cd, Cu, Ni, Zn, and Cr) in soil, aerial and root biomass, and extracted heavy metals by both biomasses were analysed. The sewage sludge rate showed a significant difference (p<0.05) in thistle aerial and root biomass. The highest aerial biomass (36.87 g d.w.) was obtained with the sewage sludge 100 t ha(-1) and the lowest with the control (27.84 g d.w.). In relation to root biomass, the highest value was observed in control (2.65 g d.w.) and the lowest in the sewage sludge 100 t ha(-1) (0.86 g d.w.). The content of total and available heavy metals in the soil increased for Zn and Cu with increasing sludge doses. The same trend was observed for the available Ni. However, Pb and Cd showed a different response as their availability in the soil decreased. The phytoextraction potential of heavy metals by thistle aerial biomass decreased with increasing rates of sewage sludge. Maximum extraction was achieved by using sewage sludge 50 t ha(-1) in Cd>Ni>Pb>Zn>Cu>Cr.