Geochemical studies on antimony: antimony dispersion in water draining Su Suergiu mine area; removal of Sb(V) from aqueous solution by layered double hydroxides (LDH)

Antimony (Sb) is considered a pollutant of priority interest, it is largely used in several industrial sectors (> 100,000 tons year worldwide) and is heavily mined worldwide (Leuz et al., 2006). In this work the hydrogeochemical behavior of Sb has been studied in water draining the abandoned antimony mine of Su Suergiu, SE Sardinia. Waters flowing at Su Suergiu show high Sb concentration and impact the main river of South Sardinia, the Flumendosa River that supplies water for agricultural and domestic uses. The main source of contamination at Su Suergiu is represented by the foundry slag heaps, in fact the slag drainages contain up to 30,000 μg L-1 Sb(tot) (median value 13,000 μg L-1 Sb(tot)). The determination of Sb specie in solution has been carried out through the analyses of both Sb(tot) (by ICP-MS and/or ICP-OES) and Sb(III) (by ASV). The Sb(III) concentration was determined on filtered (pore-size 0.45 μm) water samples stabilized with L(+) tartaric acid plus nitric acid, that, among several stabilizations of Sb(III) tested, has been evaluated as the most effective. Results obtained, showed that Sb(V) prevails in water sampled at Su Suergiu and surrounding area as Sb(OH)6̄ species, in agreement with the circumneutral-slightly alkaline pH values and oxidizing condition (Sb(III) ≤6% of Sb(tot)). The Sb(V) is less toxic but more mobile than Sb(III); the Sb behavior in water analyzed seems to be conservative, and the most important natural attenuation process of Sb contamination appears to be dilution. First in the water of Riu Ciurixeda (whose catchment collect all mine drainage), and after in the Flumendosa River, the Sb concentration decreases significantly, from 104 to 101 μg L-1, but in the Flumendosa River it still exceeded the limit recommended by both the World Health Organization (20 μg L-1) and the European Union (5 μg L-1), especially under extremely high flow conditions (Sb(tot) = 51 μg L-1; median relative to all flow conditions Sb(tot) = 22 μg L-1). In view of these results Sb(V) removal from solution was tested using a synthetic mineral belonging to the class of layered double hydroxides, that has the advantage, with respect to the other sorbents (metal oxy-hydroxides, organic polymers, etc...), of being able to remove contaminants from solutions at circumneutral pH values often found in the environment. The LDH are characterized by a layered structure composed by brucite-like sheets ([M2+1-xM3+x(OH)2]x+), stacked along the c axis and positively charged, due to the partial substitution of bivalent cations (M2+ = Mg2+, Zn2+, Ca2+) by trivalent cations (M3+ = Al3+, Fe3+). The positive charges are compensated by anions or anionic complexes (An- = Cl-, NO3-, CO32-) in the interlayer, where also structural water can occur. From an environmental point of view, LDH have anion exchange capacity, sorption capacity, high specific surface area and the “memory effect”, which is the capacity of the calcined phases which have undergone structural collapse from the loss of interlayer water and anions, to recover its structure when immerged in aqueous solution. Calcined and nitrate LDH were tested; the calcined resulted are the most effective. Among them the Mg(AlFe)-c oxides, derived from the calcination of hydrotalcite-like compounds {Mg6Al2(OH)16CO3∙4H2O}, removed Sb(OH)6̄ from solution through the rehydration and formation of a brandholzite-like compound {Mg[Sb(OH)6]2·6H2O}. The 2ZnAl-c oxides derived from the calcination of zaccagnaite-like compounds (Zn4Al2(OH)12CO3∙3H2O) kept Sb(OH)6̄ from solution by its intercalation in the interlayer during the reconstruction of zincalstibite-like LDH {Zn2Al(OH)6[Sb(OH)6]}. The Sb(OH)6̄ removal capacity of both sorbents is seriously affected by the presence of coexistent equal concentrations of As in solution, while the carbonate species and the SO42- result lower competition with respect to Sb(OH)6̄. Sorption tests with selected calcined LDH, Mg(AlFe)-c and 2ZnAl-c, were performed on water collected in the slag drainage of Su Suergiu, characterized by slightly alkaline pH and high concentration of SO42- (1006 mg L-1), HCO3̄ (485 mg L-1), As (3386 μg L-1) and Sb(tot) (9900 μg L-1). Results show substantial capacity of Sb removal from solution, and also of As. Due to the relatively low concentration of Sb in Su Suergiu water with respect to the synthetic solution used in the sorption test, the main removal process of Sb resulted for both sorbents used in the intercalation in the interlayer during the reconstruction of carbonate(hydroxyl) LDH structure, also As seem to be removed through the same mechanism. In several experiments the dissolution of sorbents was observed, therefore it is necessary consider the impact from the dissolution of the metals composing them. The solid/liquid ratio strongly influences the removal processes, therefore future studies should address this aspect to assess the potential use of LDH in Sb removal from solution at circumneutral pH usually found in the environment

Terahertz spectroscopy and global analysis of the rotational spectrum of bis-deuterated amidogen radical ND_{2}

The deuteration mechanism of molecules in the interstellar medium (ISM) is still being debated. Observations of deuterium-bearing species in several astronomical sources represent a powerful tool to improve our understanding of the interstellar chemistry. In this scenario, the doubly-deuterated form of the amidogen radical could be a target of detection in space

The rotational spectrum of 15^{15}ND. Isotopic-independent Dunham-type analysis of the imidogen radical

The rotational spectrum of $^{15}$ND in its ground electronic $X^{3}\Sigma^{-}$ state has been observed for the first time. Forty-three hyperfine-structure components belonging to the ground and v = 1 vibrational states have been recorded with a frequency-modulation millimeter-/submillimeter-wave spectrometer. These new measurements, together with the ones available for the other isotopologues NH, ND, and $^{15}$NH, have been simultaneously analysed using the Dunham model to represent the ro-vibrational, fine, and hyperfine energy contributions. The least-squares fit of more than 1500 transitions yielded an extensive set of isotopically independent $U_{lm}$ parameters plus 13 Born--Oppenheimer Breakdown coefficients $\Delta_{lm}$. As an alternative approach, we performed a Dunham analysis in terms of the most abundant isotopologue coefficients $Y_{lm}$ and some isotopically dependent Born--Oppenheimer Breakdown constants $\delta_{lm}$ [R. J. Le Roy, J. Mol. Spectrosc. 194, 189 (1999)]. The two fits provide results of equivalent quality. The Born--Oppenheimer equilibrium bond distance for the imidogen radical has been calculated [$r_e^{BO}$ =103.606721(13) pm] and zero point energies have been derived for all the isotopologues.Comment: 11 pages, 1 figure, 8 tables. Accepted for publication in Phys. Chem. Chem. Phy

Combining hydrogeochemistry, statistics and explorative mapping to estimate regional threshold values of trace elements in groundwater (Sardinia, Italy)

Assessing geochemical baseline and threshold values of potentially toxic elements at adequate scales is fundamental for distinguishing geogenic contamination from anthropogenic pollution in groundwater. This study was aimed to estimate the regional threshold values of Li, Be, B, Al, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Se, Rb, Sr, Mo, Ag, Cd, Sb, Te, Ba, Hg, Tl, Pb, Bi, and U (elements listed according to atomic numbers) in groundwater, compare results to guidelines established for drinking water and the protection of groundwater from contamination, investigate the geographical distribution of trace elements, and assess the potential influence of water-rock interaction. A pre-selection aimed at excluding groundwater samples affected by known anthropogenic activities was carefully carried out based on hydrogeochemical characteristics of waters and considering the potential sources of contamination. The resulting dataset was comprised of 1227 groundwater sampling sites located in Sardinia (Italy). Undetected values were treated using the Regression on Order Statistics method. For elements containing >75 % of undetected values and/or a limited number of samples in the dataset (Li, Rb, Sr, Mo, Ag, Te, Tl, Sb, Hg and Bi), the threshold values were estimated using either the 95th or 97.7th percentiles. For the other elements the mean + 2SD (Standard Deviation), the median + 2MAD (Median Absolute Deviation), and the TIF (Tukey Inner Fence) estimators were also calculated. Geochemical maps allowed to recognize the threshold value of each element at different scales. Regional threshold values of the regulated elements B, Al, V, Cr, Cu and Cd in groundwater were below the Italian and World Health Organization drinking water guidelines, whereas Mn and As were above them. Regional threshold values estimated with TIF exceeded the drinking water guidelines for Ni, Se, Pb and U. Results of this study showed that high concentrations of trace elements in groundwater were primarily dependent on the corresponding amount in parent materials with which the groundwater came into contact. Physical-chemical parameters and geochemical characteristics may contribute to enhancing concentrations of some trace elements in groundwater, e.g. As via reductive dissolution of Fe(III)-Mn(IV) hydroxides/oxides, Pb via formation of stable aqueous complexes, and other elements via adsorption onto fine particles with size below 0.4 μm (i.e. the pore size of filters used). Maps drawn on the centered log-ratio (clr) transformation of hydrogeochemical data, following the CoDA (Compositional Data Analysis) approach, allowed to pinpoint critical areas to be investigated in more detail. For each geological complex, groundwater samples likely representing nearly pristine conditions were identified. The monitoring of these representative groundwater samples may help to pinpoint eventual changes in environmental conditions

Geochemistry, stable isotopes and statistic tools to estimate threshold and source of nitrate in groundwater (Sardinia, Italy)

In the European Union, nitrate vulnerable zone (NVZ) should be designed for the mitigation of nitrate (NO3−) contamination caused by agricultural practices. Before establishing new NVZ, the sources of NO3− must be recognized. A geochemical and multiple stable isotopes approach (hydrogen, oxygen, nitrogen, sulfur and boron) and statistical tools were applied to define the geochemical characteristics of groundwater (60 samples), calculate the local NO3− threshold and assess potential sources of NO3− contamination in two study areas (hereafter Northern and Southern), located in a Mediterranean environment (Sardinia, Italy). Results of the integrated approach applied to two case study, permits to highlight the strengths of integrating geochemical and statistical methods to provide nitrate source identification as a reference by decision makers to remediate and mitigate nitrate contamination in groundwater. Hydrogeochemical features in the two study areas were similar: near neutral to slightly alkaline pH, electrical conductivity in the range of 0.3 to 3.9 mS/cm, and chemical composition ranging from Ca-HCO3− at low salinity to Na-Cl− at high salinity. Concentrations of NO3− in groundwater were in the range of 1 to 165 mg/L, whereas the nitrogen reduced species were negligible, except few samples having NH4+ up to 2 mg/L. Threshold values in the studied groundwater samples were between 4.3 and 6.6 mg/L NO3−, which was in agreement with previous estimates in Sardinian groundwater. Values of δ34S and δ18OSO4 of SO42− in groundwater samples indicated different sources of SO42−. Sulfur isotopic features attributed to marine SO42− were consistent with groundwater circulation in marine-derived sediments. Other source of SO42− were recognize due to the oxidation of sulfide minerals, to fertilizers, manure, sewage fields, and SO42− derived from a mix of different sources. Values of δ15N and δ18ONO3 of NO3− in groundwater samples indicated different biogeochemical processes and NO3− sources. Nitrification and volatilization processes might have occurred at very few sites, and denitrification was likely to occur at specific sites. Mixing among various NO3− sources in different proportions might account for the observed NO3− concentrations and the nitrogen isotopic compositions. The SIAR modeling results showed a prevalent NO3− source from sewage/manure. The δ11B signatures in groundwater indicated the manure to be the predominant NO3− source, whereas NO3− from sewage was recognized at few sites. Geographic areas showing either a predominant process or a defined NO3− source where not recognize in the studied groundwater. Results indicate widespread contamination of NO3− in the cultivated plain of both areas. Point sources of contamination, due to agricultural practices and/or inadequate management of livestock and urban wastes, were likely to occur at specific sites

Listeria Infection during Biologic Therapy: An Update

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New simple and low-cost methods for periodic checks of Cyclone® Plus Storage Phosphor System

The recent large use of the Cyclone® Plus Storage Phosphor System, especially in European countries, as imaging system for quantification of radiochemical purity of radiopharmaceuticals raised the problem of setting the periodic controls as required by European Legislation. We described simple, low-cost methods for Cyclone® Plus quality controls, which can be useful to evaluate the performance measurement of this imaging system

Rotational and high-resolution infrared spectrum of HC3_3N: global ro-vibrational analysis and improved line catalogue for astrophysical observations

HC$_3$N is an ubiquitous molecule in interstellar environments, from external galaxies, to Galactic interstellar clouds, star forming regions, and planetary atmospheres. Observations of its rotational and vibrational transitions provide important information on the physical and chemical structure of the above environments. We present the most complete global analysis of the spectroscopic data of HC$_3$N. We have recorded the high-resolution infrared spectrum from 450 to 1350 cm$^{-1}$, a region dominated by the intense $\nu_5$ and $\nu_6$ fundamental bands, located at 660 and 500 cm$^{-1}$, respectively, and their associated hot bands. Pure rotational transitions in the ground and vibrationally excited states have been recorded in the millimetre and sub-millimetre regions in order to extend the frequency range so far considered in previous investigations. All the transitions from the literature and from this work involving energy levels lower than 1000 cm$^{-1}$ have been fitted together to an effective Hamiltonian. Because of the presence of various anharmonic resonances, the Hamiltonian includes a number of interaction constants, in addition to the conventional rotational and vibrational l-type resonance terms. The data set contains about 3400 ro-vibrational lines of 13 bands and some 1500 pure rotational lines belonging to 12 vibrational states. More than 120 spectroscopic constants have been determined directly from the fit, without any assumption deduced from theoretical calculations or comparisons with similar molecules. An extensive list of highly accurate rest frequencies has been produced to assist astronomical searches and data interpretation. These improved data, have enabled a refined analysis of the ALMA observations towards Sgr B2(N2).Comment: 35 pages, 14 figures, accepted for pubblication in ApJ Supplemen

PRELIMINARY STUDIES ON BIOPRECIPITATION PROCESSES MEDIATED BY SULFATE REDUCING BACTERIA (SRB) AND METAL IMMOBILIZATION IN MINE IMPACTED ENVIRONMENTS.

Mining activity often leaves a critical legacy represented by huge volumes of mine wastes and residues, usually made up of highly reactive materials, which lead to the mobilization and dispersion of harmful elements in soils and waters. Although these extreme environments are adverse to the development of living organisms, it has been observed that some microorganisms are able to adapt, playing a role in metal mobility, and becoming part of the resilience of the system itself. The Iglesiente and Arburese (SW Sardinia, Italy) mine districts, now abandoned, have been exploited for centuries by mining activities aimed at Pb-Zn extraction from sulfides and non-sulfides (calamine) deposits. Here, biogeochemical barriers naturally occur as an adaptation of the ecosystem to environmental stresses. Studies, from macroscale to microscale, showed that sulfate-reducing bacteria (SRB) may influence metal mobility by mediating the precipitation of secondary authigenic metal sulfides under reducing conditions. Specifically, framboids of Zn sulfides and Fe sulfides have been observed in the sections of stream sediments core characterized by the presence of abundant organic matter, especially residues of vegetal tissues (e.g. roots and stems of Juncus acutus and Phragmites australis). Laboratory-scale experiments were performed to better understand the bioprecipitation processes. For this purpose, anaerobic batch tests were carried out using high polluted mining waters (Zn and sulfate concentrations up to 102 and 103 mg/l, respectively) inoculated with native selected sulfate-reducing bacteria from stream sediments collected in the investigated areas. Dramatic decrease (up to 100%) in Zn and sulfate was observed in solutions. Moreover, scanning electron microscopy - energy dispersive spectroscopy (SEM-EDS) analysis, performed on solids recovered at the end of the experiments, showed the presence of precipitates characterized by a tubular morphology and made up by S and Zn. SRB inocula were studied by next-generation sequencing (NGS) approach, with the aim to compare the microbial diversity of the different SRB communities and to search for indigenous novel metal-tolerant sulfidogenic microorganisms. These findings represent a valuable step forward to plan effective bioremediation strategies for reducing metal mobility and dispersion. Also, bioprecipitation mediated by SRB can have great potentialities for metal recovery and our results can help to develop biomining techniques. The authors acknowledge CESA (E58C16000080003) from RAS and RAS/FBS (F72F16003080002) grants, and the CeSAR (Centro Servizi d'Ateneo per la Ricerca) of the University of Cagliari, Italy, for SEM analysis

<i>Mycoplasma agalactiae</i> MAG_5040 is a Mg²⁺-dependent, sugar-nonspecific SNase recognised by the host humoral response during natural infection

In this study the enzymatic activity of Mycoplasma agalactiae MAG_5040, a magnesium-dependent nuclease homologue to the staphylococcal SNase was characterized and its antigenicity during natural infections was established. A UGA corrected version of MAG_5040, lacking the region encoding the signal peptide, was expressed in Escherichia coli as a GST fusion protein. Recombinant GST-MAG_5040 exhibits nuclease activity similar to typical sugar-nonspecific endo- and exonucleases, with DNA as the preferred substrate and optimal activity in the presence of 20 mM MgCl2 at temperatures ranging from 37 to 45uC. According to in silico analyses, the position of the gene encoding MAG_5040 is consistently located upstream an ABC transporter, in most sequenced mycoplasmas belonging to the Mycoplasma hominis group. In M. agalactiae, MAG_5040 is transcribed in a polycistronic RNA together with the ABC transporter components and with MAG_5030, which is predicted to be a sugar solute binding protein by 3D modeling and homology search. In a natural model of sheep and goats infection, anti-MAG_5040 antibodies were detected up to 9 months post infection. Taking into account its enzymatic activity, MAG_5040 could play a key role in Mycoplasma agalactiae survival into the host, contributing to host pathogenicity. The identification of MAG_5040 opens new perspectives for the development of suitable tools for the control of contagious agalactia in small ruminants