ENERGETIC CROPS AND COMPOST FOR THE RECLAMATION OF CONTAMINATED SOILS FROM A MARGINAL URBAN AREA IN TARANTO (ITALY) BY PHYTOREMEDIATION: CHEMICAL AND MICROBIOLOGICAL SOIL QUALITY IN EX-SITU POT TRIALS

Phytoremediation represents a highly important strategy for the enhancement and extensive management of contaminated sites. The facilities employing these technologies offer various ancillary benefits, such as employment opportunities, non-food agricultural production, urban renewal, and the creation of ecological protection areas, which compensate for the typical decontamination slowness. The plant species choice and soil preparation play a crucial role in influencing the rhizosphere ability to retain (phytostabilization), degrade, and remove (phytoextraction) contaminants. The use of amendments, compost, or manure can alter the solubility of contaminants, support microbial activity, and promote plant growth. Positive interactions between plants and soil microbiota are known to enhance nutrient uptake and improve tolerance to stress caused by pollutants. In this study, Brassica juncea and Sorghum bicolor, energy crops employed in biomass production, were tested in ex-situ pot trials to assess the remediation potential of soil contaminated with polychlorinated biphenyls (PCB), heavy hydrocarbons, polycyclic aromatic hydrocarbons (PAH) and trace elements (Cu, Sn, Pb and Zn). Two different compost amendments were tested as biostimulant conditioners. At the end of the trial, the effect of different plant and compost combinations on pollutant removal, soil biochemical indicators, microbial composition, and biomass production were evaluated. The results highlighted that adding compost increased the biomass of both plant species, although it slowed down the degradation of heavy hydrocarbons. Moreover, compost addition partially improved microbial biomass carbon (MBC) and altered soil microbiota composition and diversity, especially favoring Sphingomonadaceae and Nocardioidaceae to the expense of Bacillaceae. Finally, the presence of compost promoted the biomass yield of Sorghum, indirectly contributing to higher absolute removal and translocation of Pb and Cu. Experimental evidence indicated that the choice of plants and the use of amendments have a significant impact on soil quality and microbial communities, as well as on the overall success of the phytoremediation, since it heavily relies on economic (biomass) and social outputs as the soil remediation per se is extremely time-consuming.