Sardinia was known as an important mine pole in Europe during his history. Still after decades from mine closure, 75.000.000 m 3 of mine waste, rich in heavy metals, were left abandoned causing a huge environmental legacy on the mine district area. Consequently, cost effective remediation is required. In this frame, phytoremediation is considered a feasible candidate. This research was focused on Helichrysum microphyllum subsp. tyrrhenicum, which is pioneer in xeric soils with low-functions, like mine tailings. The aim of this study was to evaluate its ability to extract heavy metals from mine soils and accumulate them in plant tissues and its suitability for phytostabilization. Sundry samples of soil, roots and epigean organ were collected through field sampling and analysed in order to obtain metals concentration and mineralogical characteristics. Our results indicate that this species tolerates high concentration of zinc, lead and cadmium, behaving as a species suitable for phytostabilization.

Environmental contamination due to human activities is a worldwide problem that has led to the development of different remediation techniques, including biotechnological approaches such as phytoextraction and phytostabilization. These techniques take advantage of pioneer plants that naturally develop tolerance mechanisms to survive in extreme environments. A multi-technique and multi-disciplinary approach was applied for the investigation of Helichrysum microphyllum subsp. tyrrhenicum samples, bulk soil, and rhizospheres collected from a metal-extreme environment (Zn-Pb mine of Campo Pisano, SW Sardinia, Italy). Zinc, Pb, and Cd are the most abundant metals, with Zn attaining 3 w/w% in the rhizosphere solid materials, inducing oxidative stress in the roots as revealed by infrared microspectroscopy (IR). X-ray diffraction (XRD), scanning electron microscopy (SEM), and chemical analysis coupled with synchrotron radiation-based (SR) techniques demonstrate that quartz, dolomite, and weddellite biominerals precipitate in roots, stems, and leaves, likely as a response to environmental stress. In the rhizosphere, Zn chemical speciation is mainly related to the Zn ore minerals (smithsonite and hydrozincite) whereas, in plant tissues, Zn is primarily bound to organic compounds such as malate, cysteine, and histidine molecules that act as metal binders and, eventually, detoxification agents for the Zn excess. These findings suggest that H. microphyllum subsp. tyrrhenicum has developed its own adaptation strategy to survive in polluted substrates, making it a potential candidate for phytostabilization aimed at mitigating the dispersion of metals in the surrounding areas.

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The mitigation of metals contamination is currently a crucial issue for the reclamation of mine sites. Indeed, mine wastes are often disposed in open dumps and consequently pollutants are subjected to dispersion in the surrounding areas. In this study, the potential use of Helichrysum microphyllum subsp. tyrrhenicum for phytostabilization was evaluated in ex situ conditions. Ninety specimens were randomly selected and were planted in three substrates (reference substrate, mine waste materials, and mine wastes with compost). Mineralogical compositions of substrates, rhizosphere, and roots were assessed through X-ray diffraction (XRD). Zn, Pb, and Cd concentrations of substrates, rhizosphere, soil pore waters, and plant tissues were determined. The phytostabilization potential was determined through the application of biological accumulation coefficient (BAC), biological concentration factor (BCF), and translocation factor (TF). Moreover, survival and biometric parameters were assessed on plant specimens. The polluted substrates and related rhizosphere materials were mainly composed of dolomite, quartz, pyrite, and phyllosilicate. Zn was the most abundant metal in substrates, rhizosphere, and soil pore waters. XRD analysis on roots showed the presence of amorphous cellulose and quartz and Zn was the most abundant metal in plant tissues. H. microphyllum subsp. tyrrhenicum restricts the accumulation of the metals into roots limiting their translocation in aereal parts, indicating its potential use as phytostabilizer (BCF, BAC, TF < 1). Survival and growth data showed a great adaptability to different substrates, with an evident positive effect of the implementation of compost which increased the plant survival and decreased the metals uptake into roots.