The suitability for aided phytoremediation of Cynara cardunculus L. var. altilis and municipal solid waste compost (MSWC) applied at 2% and 4 % rates was evaluated in a multi potentially toxic element (PTE)-contaminated mining soil (Pb ~ 15,383 mg kg−1, Zn ~ 4076 mg kg−1, As ~ 49 mg kg−1, Cd ~ 67 mg kg−1, Cu ~ 181 mg kg−1, and Sb ~ 109 mg kg−1). The growth of C. cardunculus significantly increased with compost amendment and followed the order: MSWC-4% > MSWC-2% > Control. PTE concentrations in the roots of plants grown on amended soils decreased compared with control plants (i.e., less than ~ 82, 94, and 88% for Pb, Zn, and Cd respectively). PTE translocation from roots to shoots depended on both PTE and amendment rate but values were generally low (i.e., < 1). However, PTE mineralomasses were always higher for plants grown on MSWC-amended soils because of their higher biomass production, which favored an overall PTE bioaccumulation in roots and shoots. After plant growth, labile As and Sb increased in amended soils, while labile Pb, Zn, Cu, and Cd significantly decreased. Likewise, dehydrogenase and urease activities increased significantly in planted soils amended with MSWC. Also, the potential metabolic activity and the catabolic versatility of soil microbial communities significantly increased in planted soils amended with MSWC. Overall, our results indicate that C. cardunculus and MSWC can be effective resources for the aided phytoremediation of multi PTE-contaminated soils.
In this study, the effectiveness of softwood-derived biochar (BC) in the retention of potentially toxic elements (PTE, i.e., Cu(II), Pb(II), As(V), and Sb(V)) was evaluated at different pH values (4.5, 6.0, and 7.0), along with its capacity to alleviate PTE phytotoxicity. At all pH values, sorption and kinetic isotherms followed the trend: Pb(II) (e.g., ~ 0.56 mmol g−1 at pH 6.0) > Cu(II) (e.g., ~ 0.33 mmol g−1 at pH 6.0) > As(V) (e.g., ~ 0.29 mmol g−1 at pH 6.0) > Sb(V) (e.g. ~ 0.24 mmol g−1 at pH 6.0). Kinetic data strongly correlated with the pseudo-second-order kinetic equation; Langmuir and Freundlich isotherm models suggested monolayer sorption of Cu(II), Pb(II), and As(V) onto the BC surface and the interaction of Sb(V) with BC sites characterized by distinct sorption energy (i.e., multilayer sorption). Scanning electron microscopy (SEM) with energy-dispersive X-ray (EDX) analysis of PTE-saturated BC showed that Pb(II) was mainly associated with O, Sb(V) with Ca and Fe, while Cu(II) and As(V) with Fe and O. This suggested that hydroxyl and carboxyl functional groups, amorphous Fe oxy-hydroxides, as well as PTE precipitation with BC components were likely responsible for BC sorption capacity. Treatment of PTE-saturated BC with Ca(NO3)2 and a range of environmentally relevant organic acids indicated that 6–11% of PTE were loosely bound and easily exchangeable, while up to 60% could be mobilized by the organic acids. Hydroponic plant-growth experiments using triticale plants showed that BC stimulated plant growth in the presence of PTE and reduced their phytotoxicity.
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