Search

The seed germination of Helichrysum microphyllum subsp. tyrrhenicum, an endemic species of Sardinia and Corsica with metal tolerance capability, was evaluated against zinc (Zn; 0, 250, 500 and 1000 mg/L) and lead (Pb; 0, 25, 50 and 100 mg/L) stress. Seeds were collected in three localities: (a) inside a mine dump highly polluted with these metals, (b) outside but close to this area and (c) far from the metal-polluted site. Germination responses were assessed at 10, 15 and 20 °C, and the percentage, time of germination and mortality of seedlings were evaluated. The taxon showed a high capacity to germinate under Zn and Pb stress, and the germination was never completely inhibited; however, the germination decreased with increasing Zn concentrations, but not under Pb stress. Moreover, the seeds from specimens growing in mining sites appeared to be less affected by Zn stress than seeds coming from the other localities. A successful survival of seedlings during the first days of their development under metal stress and under controlled conditions was detected. Our study suggests that this species may give an important contribution to future phytoremediation programs on mining sites, in which it could be spread by seeds in order to form a vegetation cover. [ABSTRACT FROM AUTHOR]

An amorphous Zn biomineralization ('white mud'), occurring at Naracauli stream, Sardinia, in association with cyanobacteria Leptolyngbya frigida and diatoms, was investigated by electron microscopy and X-ray absorption spectroscopy. Preliminary diffraction analysis shows that the precipitate sampled on Naracauli stream bed is mainly amorphous, with some peaks ascribable to quartz and phyllosilicates, plus few minor unattributed peaks. Scanning electron microscopy analysis shows that the white mud, precipitated in association with a seasonal biofilm, is made of sheaths rich in Zn, Si, and O, plus filaments likely made of organic matter. Transmission electron microscopy analysis shows that the sheaths are made of smaller units having a size in the range between 100 and 200 nm. X-ray absorption near-edge structure and extended X-ray absorption fine structure data collected at the Zn K-edge indicate that the biomineral has a local structure similar to hemimorphite, a zinc sorosilicate. The differences of this biomineral with respect to the hydrozincite biomineralization documented about 3 km upstream in the same Naracauli stream may be related to either variations in the physicochemical parameters and/or different metabolic behavior of the involved biota. [ABSTRACT FROM AUTHOR]

Several decades after the closure of the Ingurtosu mine (SW Sardinia), a variety of seasonal Zn biomineralizations occurs. In this work, waters, microbial consortia, and seasonal precipitates from the Naracauli stream were sampled to investigate chemical composition of stream waters and biominerals, and microbial strain identity. Molecular and morphological analysis revealed that activity of dominant cyanobacterium Leptolyngbya frigida results in precipitation of Zn silicate. The activity of the cyanobacterium was associated to other bacteria and many kind of diatoms, such as Halamphora subsalina and Encyonopsis microcephala, which are trapped in the process of biomineral growth. In this work, the precipitation process is shown to be the result of many different parameters such as hydrologic regime, microbial community adaptation, and biological mediation. It results in a decrease of dissolved Zn in the stream water, and is a potential tool for Zn pollution abatement. [ABSTRACT FROM AUTHOR]

A monitoring survey of the coastal area facing the industrial area of Portoscuso-Portovesme (South-Western Sardinia, Italy) revealed intense bioerosional processes. Benthic foraminifera collected at the same depth (about 2m) but at different distances from the pollution source show extensive microbial infestation, anomalous Mg/Ca molar ratios and high levels of heavy metals in the shell associated with a decrease in foraminifera richness, population density and biodiversity with the presence of morphologically abnormal specimens. We found that carbonate dissolution induced by euendoliths is selective, depending on the Mg content and morpho-structural types of foraminiferal taxa. This study provides evidences for a connection between heavy metal dispersion, decrease in pH of the sea-water and bioerosional processes on foraminifera. [ABSTRACT FROM AUTHOR]

Abstract: The Rio Naracauli in SW Sardinia drains part of the Ingurtosu Zn–Pb mining district, and contains extreme concentrations of dissolved Zn at near-neutral pH. In the upper reaches of the stream, pH, alkalinity and Zn concentrations are such that hydrozincite [Zn5(CO3)2(OH)6] precipitates in a biologically mediated process facilitated by a microalga (Chlorella sp.) and a cyanobacterium (Scytonema sp.). Values of δ66Zn in water and solid samples ranged from −0.35‰ to +0.5‰ relative to the JMC 3-0749-Lyon standard, and closely follow a mass-dependent fractionation line. Two composite samples of sphalerite, the primary ore mineral in the Ingurtosu deposits, had an average δ66Zn of +0.15‰, similar to sphalerite measured elsewhere in hydrothermal mineral deposits. Zinc isotope measurements of the stream water and the hydrozincite forming in the stream show a consistent preference for the heavy isotope, 66Zn, in the hydrozincite relative to 64Zn. Synthetic hydrozincites produced without added bacteria have δ66Zn identical to the dissolved Zn, thus suggesting a biologically mediated mineralization process in Rio Naracauli. The average fractionation, Δhdz-water, is 0.35‰, the magnitude of which is consistent with other studies, and suggests an extracellular mechanism of the biomineralization process. Zinc concentration and dissolved δ66Zn steadily decrease in the reach of the stream where the biomineralization occurs. The biomineralization process also leads to the sequestration of Pb, Cu and Ni in the hydrozincite lattice, and the coeval precipitation of an amorphous CdCO3 solid, prompting the suggestion that if optimized, the biomineralization process might represent a feasible passive remediation strategy for streams with high Zn and other metals, and with near-neutral pH. [Copyright &y& Elsevier]

The Sulcis-Iglesiente district (SW Sardinia, Italy) is one of the oldest and most important polymetallic mining areas in Italy. Large outcrops of sulfide and oxide ores, as well as the products of the long-lasting mining activity, are present throughout the district releasing significant quantities of metals and metalloids into the surrounding environment. Here are reported concentrations of 21 elements determined in scalp hair samples from children (aged 11–13 years) living in different geochemical environments of southwestern Sardinia: Iglesias, hosting several abandoned mines, and the island of Sant׳Antioco, not affected by significant base metal mineralization events. Trace element determinations were performed by ICP-MS. Statistically significant differences ( p <0.01) in elemental concentration levels between the two study sites were found. Hair of children from Iglesias exhibited higher concentration values for Ag, Ba, Cd, Cr, Ni, Pb, Rb, Sb, U, V, and Zn. Rubidium, V and U resulted more abundant at Sant׳Antioco. Hair samples from Iglesias showed gender-related differences for a larger number of elements (Ag, Ba, Cd, Co, Cu, Ni, Sr, U and Zn) than at Sant׳Antioco, where only U was significantly different. The above elemental concentrations in females were always higher than in male donors. Robust Principal Component Analysis operated on log-transformed elemental concentrations showed components indicative of a) sulfides ore minerals (PC1) reflecting the influence of the diffuse mineralization covering the entire study area, b) the presence of some bioavailable As sources (PC2) as As-rich pyrite and Fe-containing sphalerite and c) other sources of metals overlapping the diffuse mineralizations, as carbonate rocks and coal deposits (PC3). The results provided evidence of a potential risk of adverse effects on the health of the exposed population, with children living at Iglesias being greatly exposed to several metals and metalloids originated in mining tailings, enriched soils, waters and food. [ABSTRACT FROM AUTHOR]

Abstract: Hydrozincite [Zn5(CO3)2(OH)6] precipitation from Naracauli waters (SW Sardinia) is, among other things, promoted by a microbial community made up of a filamentous cyanobacterium (Scytonema sp.) and a microalgae (Chlorella sp.). Hydrozincite bioprecipitation is responsible for the natural removal of harmful metals, especially Zn, from the stream waters. Thus, hydrozincite could be used to attenuate metal pollution in mining waters. Information on environmental conditions which promote the biomineralization process is fundamental for the development of remediation strategies. This paper aims to investigate the variables controlling the biomineralization process, and seasonal variation of the hydrochemical factors that affect hydrozincite precipitation. Hydrozincite morphology varies depending on the environmental conditions. Specifically, changes were observed between samples collected in late spring and samples collected in summer, and among samples precipitated under different water flow conditions. According to field observations, correlated with speciation and equilibrium calculation, the maximum intensity in hydrozincite precipitation occurs in the late spring during rainy years. In these conditions, the hydraulic regime in the stream reaches stationary conditions, and saturation index values with respect to hydrozincite reach their highest values. Concomitantly, the Zn2+/ molar ratio reaches values close to 1, indicating that kinetic processes have a role on the hydrozincite biomineralization process. [Copyright &y& Elsevier]

• The Montevecchio-Ingurtosu district was one of the largest Italian Pb-Zn-Ag producers. • New field, microscopic, microchemical, isotopic, and fluid inclusion data were obtained. • The Montevecchio deposit shows several affinities with the class of Ag-Pb-Zn veins in metasediments as defined by Beaudoin & Sangster (1992). • Ore textures and mineralogical-chemical features at all scales document a multistage process of mineralization postdating the emplacement of the 304 ± 4 Ma Arbus pluton, and occurring in a tectonically active regime. • The exact age of mineralization is not constrained, although it might be related to regional, large-scale shear deformation in a late-post-orogenic context. • At least part of the mineralization is associated with relatively low temperature (≦200 °C), high salinity (>20 wt% equiv. mass NaCl) fluids analogous to basinal brines. The Montevecchio-Ingurtosu district (SW Sardinia) was among the largest historical Pb-Zn producers of Italy, with significant Ag output, and yields of metallic byproducts such as Cd, Co, Cu, Bi, Sb, Ge, In, and Ga. Despite this importance, detailed descriptions of orebodies and mineral assemblages are surprisingly scarce and old. Here we summarize all previously available information and contribute new textural, microchemical, fluid inclusion, and C-O isotopic data deriving from a recent sampling of currently exposed orebodies. Mineralization occurs as steeply dipping veins extending for almost 20 km at the northern and western flanks of the Variscan Arbus pluton; veins are hosted in phyllites of the Arburese Unit close to the thermometamorphic aureole. Ore enrichments range from massive to coarsely nodular, stockwork and brecciated. Vein filling consists of siderite (locally Zn-rich), quartz, sphalerite, galena (remarkably rich in micro-inclusions), with accessory chalcopyrite, fahlore, bournonite, barite, and Ni-Co sulfarsenides. Vein assemblages may vary, even within a single vein, from sphalerite- to galena-dominated. Cu-rich assemblages (fahlore + chalcopyrite) were locally observed. Wallrock is affected by silicification, sericitization and pyrite dissemination. Sphalerite shows a complex mineral chemistry, with marked variations in Fe (0.08 to 8.9 mol% FeS) and in Cd contents (from <0.05 to >1 wt%). Trace element analyses (LA-ICP-MS) document the presence of measurable amounts of Ga, Ge, In, Ag, Ni, Co, Tl and Mo. Fahlore varies from the Sb (tetrahedrite) and the As (tennantite) endmembers, with Ag-rich compositions corresponding to Sb endmembers. The occurrence of Cd-rich tetrahedrite (up to 14.5 wt%) is remarkable. Fluid inclusion studies on sphalerite and quartz are in agreement with previous literature data, and indicate comparatively low (in the range 90°–130 °C) homogenization temperatures (T h) and high salinities (14 to 25 equiv. mass % NaCl); both microthermometric data and SEM/EDS analyses of decrepitated inclusions indicate the presence of Ca and K beside Na. Pressure correction to T h is presumably low (in the order of 10 °C), considering a hydrostatic pressure regime. Application of the sphalerite-based GGIMFiS thermometer provided temperatures in excellent agreement with fluid inclusion data for the Montevecchio mineralization. Isotopic data on Montevecchio carbonates define mildy negative δ13C PDB values (between −1 and −5 per mil), and a larger spread of δ18O SMOW values, between +14 and +20 per mil. Other isotopic data from literature include a limited set of δ34S values for galena, sphalerite and pyrite, and a fairly large body of Pb isotopic data on galena. Comparatively narrow ranges for sulfur isotope signatures suggest a homogeneous, possibly igneous, sulfur source, whereas the large spread in Pb isotope signatures reflects the large-scale character of the hydrothermal process and indicates that the Arbus pluton may have been just one of the sources of ore lead. The Montevecchio vein system shows affinities with other late to post Variscan European deposits. The nature of the mineralizing fluids at Montevecchio is analogous to low temperature, basinal brines, and typical of several regional-scale, late to post-Variscan hydrothermal events across Europe. Mineralization at Montevecchio obviously postdates the emplacement of the Arbus plutonic complex, but its exact age remains unknown.. [ABSTRACT FROM AUTHOR]