Metal Tolerance Capability of Helichrysum microphyllum Cambess. subsp. tyrrhenicum Bacch., Brullo & Giusso: A Candidate for Phytostabilization in Abandoned Mine Sites

Abstract

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.

Mineralogy and Zn Chemical Speciation in a Soil-Plant System from a Metal-Extreme Environment: A Study on Helichrysum microphyllum subsp. tyrrhenicum (Campo Pisano Mine, SW Sardinia, Italy)

“…Zinc is the most abundant metal in the bulk soils (24,900 CP -32,700 OCP mg/kg), rhizospheres (26,300 CP -27,300 OCP mg/kg) and in the plant tissues (890 OCP -3290 CP mg/kg), followed by Pb (1240 OCP -5000 CP mg/kg in the soils, 1600 OCP -5030 CP mg/kg in the rhizospheres, and 50 OCP -1020 CP mg/kg in the plant tissues) and Cd (100 CP -340 OCP mg/kg in the soils, 170 CP -280 OCP mg/kg in the rhizospheres, and 13 OCP -31 OCP mg/kg in the plant tissues). It should be noted that metal contents detected in this work are of the same order of magnitude as in previous studies [39,41,46,91], in which relevant local variations due to heterogeneities of the mine tailings can be highlighted. [92] 1208 954 BCF, BAC, and TF (Table 3) were calculated to investigate the transfer of metals from geosphere to plant tissues and their translocation from the roots to the epigean organs.…”

“…This structure was also detected by STXM ( Figure 6), also showing that Zn is mainly stored in the root epidermis. Moreover, the presence of Zn in the epidermis is consistent with previous study carried out on this plant species [39,46,47] that demonstrated its tolerance towards Zn via a metal exclusion strategy. In the rhizosphere, XAS analysis showed that Zn is mainly present as smithsonite, hydrozincite, and Zn sulfate, resulting from the oxidation of the primary Zn sulfides [110][111][112].…”

“…The chemical analysis of bulk soils and rhizosphere materials (Table 2) from the mine dump (CP samples) showed that metal contents (Zn 24,900-26,300 mg/kg, Pb 5000-5030 mg/kg, Cd 100-170 mg/kg) are extremely well above the threshold limits imposed by Italian laws (D.lgs. 152/2006 [90]) for sites for industrial use (Zn 1500 mg/kg, Pb 1000 mg/kg, Cd 15 mg/kg), supporting previous works carried out in the same study area and confirming the high Zn, Pb, and Cd contamination [39,41,46,91]. Also values from OCP samples exceed the Italian pollution thresholds probably due to the aeolian dispersion of fine particles from the nearby tailing dump.…”

“…Nevertheless, insights from this study are of relevant interest to develop sustainable phytoremediation techniques. Helichrysum tyrrhenicum is an unquestioned candidate for phytostabilization [39,47,48] mainly because (i) it offers a long-term plant canopy, (ii) it can reduce the erosion processes and the release of pollutants in soil and air, and (iii) it can reactivate the pedological and vegetational dynamics. Further investigations will be needed to better elucidate the plant-microbe interactions, their impact on vegetational dynamics, and the potential role of plant growth-promoting bacteria on metal accumulation.…”

Phytoremediation: a sustainable environmental technology for heavy metals decontamination

“…Erica australis possesses the ability to uptake Cu, Cd and Pb via its roots without any sign of damage and suggest as a phytostabilizator species [123]. Bacchetta et al [13] indicated that Zn, Cd and Pb uptake was restricted largely in root tissue of Helichrysum microphyllum which is suitable for phytostabilization.…”