Grass and legume species and municipal wastes as bioresources for the assisted phytostabilization of PTE-contaminated soils Matteo Garau, Giovanni Garau, Stefania Diquattro, Maria Vittoria Pinna, Paola Castaldi Dipartimento di Agraria, University of Sassari, Viale Italia 39, 07100 Sassari, Italy
Assisted phytoremediation, i.e. the combination of amendment and plant to remove potentially toxic elements (PTE) from soil, or to reduce their mobility and toxicity, can represent an effective gentle remediation option for the recovery of PTE-contaminated soils. The aim of this study was to evaluate the suitability of selected grass and legume species, such as Arundo donax L., Hordeum vulgare L. and Lupinus albus L., in assisted phytoremediation programs of PTE-contaminated soils in combination with a municipal solid waste compost (MSWC), which was used at 2 and 4 % rates. The soil investigated had a subacidic pH (5.93) and was heavily contaminated by different PTE, i.e. Pb (15,383 mg kg−1), Zn (4,076 mg kg−1), Cu (181 mg kg−1), Sb (109 mg kg−1), Cd (67 mg kg−1) and As (49 mg kg−1). The addition of MSWC at 2 and 4% rates significantly decreased the labile fractions of most PTE and at the same time increased the residual fractions of Zn and Sb. Soil enzyme activities, i.e. dehydrogenase and β-glucosidase, were significantly enhanced in MSWC-amended soils (i.e. up to ~6.0 and 1.4 times higher in MSWC-4% than in control soil, respectively), as well as soil basal respiration, and the potential metabolic activity and catabolic versatility of soil microbial communities. Arundo donax L., Hordeum vulgare L. and Lupinus albus L. were able to grow in the contaminated soil, and their biomass was significantly influenced by compost either positively (e.g. A. donax shoots and roots) or negatively (e.g. H. vulgare roots). Overall, the PTE considered were mainly retained in root tissues [translocation factors (TF) were << 1]. Compost addition significantly decreased or did not influence the PTE uptake and bioaccumulation factors of A. donax and H. vulgare roots and shoots, while it increased those of L. albus (particularly in roots) with respect to As, Sb, Pb and Cu. Finally, MSWC increased the PTE removal efficiency by A. donax (and partially by L. albus but not by H. vulgare) which showed the highest PTE mineralomasses when grown on 4 % MSWC. Overall, the results obtained suggested that MSWC, particularly at 4% rate, could be useful to stabilise the PTE in sub-acidic contaminated soils and to increase the microbial activity and functionality in these latter soils. In addition, A. donax, and in selected cases L. albus, appeared as useful bioresources that can be used in combination with MSWC for the assisted phytostabilization of PTE-contaminated soils. Further studies are needed in order to investigate the effectiveness of these crops in rotation and/or when intercropped in assisted phytoremediation programs under field conditions.
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