Investigation on Revegetation/ Phytoremediation of Campo Pisano abandoned mine area

The contaminated mine tailings rich in toxic metals pose serious environmental threats to the surrounding areas. The reclamation of these mine sites is an economically costly and technically complex process. Phytoremediation is one of the most promising techniques for sustainable, cost-effective and eco-friendly remediation of contaminated mine sites. Pinus halepensis Mill. was selected due to its special characteristics as a pioneer species growing spontaneously on Campo Pisano (CP) mine tailing, a multiple heavy metal contamination site in SW-Sardinia, Italy. The aim of this PhD thesis is to assess the phytoremediation capability of P. halepensis and focuses on assessing: • the main geochemical and mineralogical characteristics of the soil-plant system through X-ray diffraction (XRD) and scanning electron microscopy (SEM) • Zn,Pb and Cd concentration and its bioavailable fractions in contaminated substrates • the metal accumulation and translocation behaviour in P. halepensis compartments (roots, barks, wood and needles) by calculating the Biological Accumulation Coefficient (BAC), the Translocation (TF) and the Biological Concentration Factors (BCF) • the geochemical forms of Zn, Pb, Cd and their bioavailability through the three-step BCR extraction method in relation to the Physico-chemical and mineralogical characteristics of the soil in-depth and the soil-root system • the phytostabilization potential of seedlings planted under the controlled-greenhouse condition in four different substrates (reference, CP mine tailings, mine tailings amended with compost, mine tailing with their pine and substrates) to evaluate: - the bioavailability of metals and their accumulation in roots and the aerial parts - the plant survival, elongation and biomass production - the mitigation of metal stress in plant by assessing the effectiveness of compost amendment. The outcome of XRD and SEM analysis showed the presence of pyrite, dolomite, calcite, quartz, gypsum and barite with iron sulfate and iron oxide in the polluted substrates. Zn ore minerals and muscovite were mostly detected in the deeper soil layers. Iron sulfate was found mainly in the substrate around the plant roots indicated the presence of some minerals that were discharged in the mine waste and the pyrite dissolution reaction. Zn was the most abundant metal in the substrate as well as plant tissues. The high Zn, Pb and Cd accumulation in the root of P. halepensis reflects the high metal contamination in soil. The BCR analysis showed that the uppermost alkaline-calcareous layers of mine waste were affected by the rich carbonate lithology and mineralogy of CP which were different from the deeper acidic layers. It showed that Pb and Zn were less bioavailable for roots and were often found in the residual fraction, mainly in deep layers of the compost-amended soil, while Cd was found in the exchangeable BCR fraction. The presence of Zn and Pb ore minerals having low solubility, or the rhizosphere interaction processes may cause their resistance to leaching in BCR extraction. The outcome of the greenhouse investigation declared the potential of P. halepensis to tolerate high metal concentrations, and its adaptation to survive in highly contaminated substrates as well as its aptitude to limit metal accumulation and translocation to the aerial parts. The addition of compost enhanced the soil organic carbon and nitrogen contents and restricted the metal bioavailability and accumulation in the aerial parts of plant, however, it didn’t improve the plant survival and growth. These outcomes together with the low biological accumulation and translocation indexes (BCF,TF,BAC<1) for all plant tissues indicated that P. halepensis is an excluder, tolerates high Zn, Pb, and Cd concentrations, restricts their accumulation and translocation to the aerial parts and may be potentially eligible for long-term phytostabilization projects in abandoned mine tailing sites.