Application of phytoremediation technique for removal of polycyclic aromatic hydrocarbons and potential toxic elements from contaminated soils

The issue of polycyclic aromatic hydrocarbons (PAHs) and potential toxic elements (PTEs) is widespread in soils involving environmental systems and human health. At the same time, research on eco‒friendly alternatives for the treatment of PAH and PTE-contaminated soils and their reuse after remediation must be stepped up. Among effective treatments employed to remediate contaminated soils with PAHs and PTEs, phytoremediation gained increasing attention due to its eco-friendly interaction and cost-effectiveness features. For this purpose, this doctoral thesis firstly examined the phytoremediation influencing factors involved in the removal of PAHs and PTEs from contaminated soils. In a realistic approach, soil organic matter (SOM), plant species, environmental parameters (pH, soil oxygenation, and temperature), bioavailability, autochthonous microorganisms, and vegetation competition and resulted among the main parameters affecting PAHs and PTEs removal through phytoremediation. Phytoremediation was confirmed to be a good alternative to conventional physical-chemical and thermal methods, as the latter may cause serious chemical modification of the site and interference with ongoing activities. Among different plant species, the application of Cannabis sativa L. in phytoremediation of contaminated soils represent a promising remediation strategy, also to implement encouraging feedbacks in terms of land use and creation of circular schemes. In this context, the present thesis investigated 60 days phytoremediation by C. sativa L. at laboratory scale for pyrene (PYR)-contaminated soil (i.e., 50, 100 and 150 mg kg− 1 dry soil), resulting in PYR removal up to 95% in planted soil, 35% higher than in the unplanted control. The interaction between the plant roots and microorganisms in rhizosphere was likely associated with PYR removal in the study. As a proof, the highest dehydrogenase (DHO) activity, of 66.26 μg INTF g−1 dry soil, which is a possible indirect indicator related to PYR degradation was measured in the soil with the highest PYR removal. Negative effects of PYR on C. sativa L. roots and shoots development were observed, reaching a decrease up to 56 and 42 % respectively. Afterwards, the present thesis work focused on the phytoremediation of PAH and Cu-contaminated soil (i.e., 50–150 and 350 mg·kg−1, respectively) by C. sativa L. for 50 days, a very frequent condition of real polluted sites. PYR and phenanthrene (PHE) were used as model compounds for low (LMW) and high molecular weight (HMW) PAHs, respectively, in the study. PHE and PYR removal reached 93 and 61%, 98 and 48%, and 97 and 36% in the three testes conditions, respectively, while the highest Cu extraction amounted to 58 mg·kg−1. The plants biomass decreased with the increase of the initial concentration of PYR and PHE in soil. Hence, the height of the plants grown under the 300 mg ΣPAHs kg−1 condition, was found to be the lowest, reaching a final value of about 10 cm, approximately three times lower than the plants grown in the uncontaminated controls. Finally, this thesis evaluated a rough cost assessment in dollar currency for the entire phytoremediation process including seed purchase, general remediation management, required working expanse for pre-planting, planting, harvesting and post-harvesting operations. A total cost of USD 47 per ton was obtained for the 100 mg ΣPAHs kg−1, which achieved the highest PAH and Cu removal, and biomass production (i.e., 78 and 11%, and 0.32 g, respectively) compared to the other two conditions after 50 d.