Release of Arsenic from Volcanic Rocks through Interactions with Inorganic Anions and Organic Ligands

The effects of a number of inorganic anions (F⁻, HCO₃ ⁻, B(OH)₄⁻, Cl⁻, I⁻) and of the siderophore DFO-B on the release of As from volcanic rocks were investigated in batch experiments. While previously reported field and laboratory data support a role of inorganic anions on As mobilization into aquifers, the role of siderophores on As-induced mobilization was less investigated. Fluoride, bicarbonate and DFO-B have shown a significant influence on the release of As from the rocks. Lava was mostly affected among the investigated rocks at pH 6 and 20°C by releasing 4% of its initial As content in the presence of 0.01 M F⁻and 10% in the presence of 500 μM DFO-B. The effect of fluoride was larger at pH 6 than at pH 8.5 for all the rocks. In the case of DFO-B, there was also a larger effect at pH 6 compared to pH 8 for the various rocks except tuff. Bicarbonate played a role under alkaline conditions while its effect was negligible at pH 6. Anion exchange processes in the presence of fluoride and bicarbonate and complexation processes in the presence of the siderophore DFO-B appear to be the major processes responsible for the release of arsenic from the rocks. The siderophore DFO-B plays mainly an indirect role on the As release by complexing Al, Fe and Mn, thus favoring the dissolution of the rocks and the consequent release of As bound to surface Al, Fe and Mn oxy-hydroxides. These findings suggest that ionic interactions with fluoride, bicarbonate and siderophore may be a further triggering factor in the mobilization of As from aquifer rocks.     

Chlorine-rich metasomatic H2O-CO2 fluids in amphibole-bearing peridotites from Injibara (Lake Tana region, Ethiopian plateau): Nature and evolution of volatiles in the mantle of a region of continental flood basalts

Petrological and geochemical study of volatile bearing phases (fluid inclusions, amphibole, and nominally anhydrous minerals) in a spinel lherzolite xenolith suite from Quaternary lavas at Injibara (Lake Tana region, Ethiopian plateau) shows compelling evidence for metasomatism in the lithospheric mantle in a region of mantle upwelling and continental flood basalts. The xenolith suite consists of deformed (i.e., protogranular to porphyroclastic texture) Cl-rich pargasite lherzolites, metasomatized (LILE and Pb enrichment in clinopyroxene and amphibole) at T ? 1000 °C. Lherzolites contain chlorine-rich H₂O-CO₂ fluid inclusions, but no melt inclusions. Fluid inclusions are preserved only in orthopyroxene, while in olivine, they underwent extensive interaction with the host mineral. The metasomatic fluid composition is estimated: X_CO2 = 0.64, X_H2O = 0.33, X_Na = 0.006, X_Mg = 0.006, X_Cl = 0.018, (salinity = 14-10 NaCl eq. wt.%, a_H2O = 0.2, Cl = 4-5 mol.%). Fluid isochores correspond to trapping pressures of 1.4-1.5 GPa or 50-54 km depth (at T = 950 °C). Synchrotron sourced micro-infrared mapping (ELECTRA, Trieste) shows gradients for H₂O-distribution in nominally anhydrous minerals, with considerable enrichment at grain boundaries, along intragranular microfractures, and around fluid inclusions. Total water amounts in lherzolites are variable from about 150 up to 400 ppm. Calculated trace-element pattern of metasomatic fluid phases, combined with distribution and amount of H₂O in nominally anhydrous minerals, delineate a metasomatic Cl- and LILE-rich fluid phase heterogeneously distributed in the continental lithosphere. Present data suggest that Cl-rich aqueous fluids were important metasomatic agents beneath the Ethiopian plateau, locally forming a source of high water content in the peridotite, which may be easily melted. High Cl, LILE, and Pb in metasomatic fluid phases suggest the contribution of recycled altered oceanic lithosphere component in their source.     

A stratigraphic and geophysical approach to studying the deep-circulating groundwater and thermal springs, and their recharge areas, in Cimini Mountains–Viterbo area, central Italy

The stratigraphic and structural setting of the Cimini Mountains and Viterbo area of Italy has been reconstructed. The architecture of the tectonic edifice, below the Pleistocene Cimino and Vicano volcanic districts cover, is characterized by the Mesozoic–Cenozoic Tuscan Nappe and the similar Umbria-Marche Succession; both are capped by the overthrusted Ligurian Late Cretaceous–Eocene Tolfa Flysch. A shallow unconfined volcanic aquifer is separated, by a thick aquiclude, from the deep confined carbonate aquifer consisting of the Tuscan Nappe and the Umbria-Marche Succession. The volcanic aquifer hosts cold waters, whilst the carbonate aquifer hosts hot sulphate–alkaline earth waters that emerge in the thermal area of Viterbo with a temperature of 30–60°C. The recharge area of cold waters is located in the Cimini Mountains. Thermal waters of the Viterbo hot springs are derived from a circuit of waters that emerge along the River Nera near Narni (about 34 km ENE of Viterbo), with a high salinity, a temperature of 16–18°C, a sulphate–alkaline earth composition, and a discharge of 13 m³/sec, whose recharge area is located in the central pre-Apennines reliefs.     

Effects of desferrioxamine-B on the release of arsenic from volcanic rocks

Microorganisms play an important role in As mobilization into groundwater by directly influencing As speciation or indirectly inducing solubilisation from As-bearing phases, such as Fe, Mn and Al oxides. Iron oxide dissolution could also be induced by siderophores, small-molecule compounds produced by microorganisms to favour Fe uptake. Well waters exceeding the potable water limit of 10 μg As L⁻¹ (0.133 μM) have been widely reported in geothermal areas. Mechanisms responsible for these high As concentrations have not yet been thoroughly elucidated and the complexity of As mobilization in volcanic aquifers is still open to multiple interpretations. The present study was based on batch release experiments aimed at verifying and quantifying the effect of siderophores on As mobilization from volcanic rocks (lava, tuff, peperino and fallout deposit) at different pH and ligand concentration. In the experiments the siderophore trihydroxamate desferroxamine B (Dfob) was used and its effect on As release from volcanic rocks was manifest after the first days. The most favourable pH for As release was pH 6 while concentrations above 250 μM Dfob considerably enhanced As and Fe concentrations in solution. The As release from rocks was between 2.0–10% at pH 6 and 2.4–8.8% at pH 8. The As/Fe ratio in solution changed with time suggesting different release mechanisms and higher mobility of As compared to Fe during the first phase of the experiment. The presence of siderophore increased Fe dissolution rates up to 10 orders of magnitude. The As release correlated with Al, Mn, Fe, Si, V, Ga and Sb and the release of all these elements increased with increasing Dfob concentration. In alkaline environments also Cu, Zn and Pb were mobilized. The presence of siderophores represents a possible trigger for As mobilization from iron binding minerals to the water phase, with interesting implications for groundwater quality, plant uptake and bacterial communities.     

Keratose-dominated sponge grounds from temperate mesophotic ecosystems (NW Mediterranean Sea)

Differently from the North Atlantic Ocean, only few examples of sponge grounds are known from the Mediterranean Sea, mainly thriving in the deep sea. In this study, a novel temperate mesophotic ecosystem dominated by massive keratose sponges is reported from the Ligurian deep continental shelf. An extensive Remotely Operated Vehicle (ROV) survey allowed to study the structure and large-scale distribution of this biocoenosis. The sponge grounds here described are highly fragmented, being formed by a large number of dense, discrete aggregations of Sarcotragus foetidus (up to 7.7 specimens/m²) and other sponges, including Spongia lamella and Axinella polypoides. They mainly occur on flat, patchy and highly silted hardgrounds between 40 and 70 m depth. These sponge-dominated ecosystems have an exceptionally wide spatial distribution, estimated to cover up to nearly 200 hectares, with the largest sponge grounds occurring along the westernmost part of the Ligurian coast, probably in relation to more suitable oceanographic conditions. The dominant sponge species reach considerable heights (up to 65 cm), greatly increasing the habitat three-dimensionality and acting as poles of attraction for a diverse sessile and vagile fauna. In addition, the high abundance of the keratose sponge grounds at mesophotic depths might represent a larval source for shallow-water populations that in the last decades have been stricken by several mass mortality events.     

The effect of organic compounds in the oxidation kinetics of Cr(III) by H2O2

The oxidation of Cr(III) has been studied in NaCl solutions in the presence of two siderophore models, acetohydroxamic acid (Aha) and benzohydroxamic acid (Bha), the natural siderophore Desferal (DFOB) and the synthetic aminocarboxilate (ethylenedinitrilo)-tetra-acetic acid (EDTA) as a function of pH (8-9), ionic strength (0.01-2 M) and temperature (10-50 °C), at different Cr(III)-organic compound ratios. The addition of Aha and Bha caused the rates to increase at low ligand/Cr(III) ratios and decrease at high ratios. The variation of the pseudo first order rate constant (k₁) as a function of the ligand concentration has been attributed to the formation of three Cr(III)-organo species (1:1, 1:2, 1:3), which can form in the presence of monohydroxamic acids. A kinetic model has been developed that gives a value of 600 (min⁻¹) for the pseudo first order rate constant k_1CrAha²⁺ and values approaching zero for and k_1CrAha3. These kinetic results demonstrate that these monohydroxamic acids are able to bind with Cr(III) under experimental conditions that may occur in natural waters and can increase the oxidation rates of Cr(III) with H₂O₂ by a factor of 3.5 at an Aha/Cr(III) ratio of about 50-100.The monohydroxamic acids also affect the rates on aged products of Cr(III), suggesting that these ligands are able to affect the oxidation rates by releasing reactive Cr(III). DFOB and EDTA do not have a great effect on the oxidation of Cr(III) with H₂O₂. This is thought to be due to the much longer times they need to form complexes with Cr(III) compared to Aha and Bha. The rates for the formation of DFOB and EDTA complexes with Cr(III) are not competitive with the rates of the formation of aged Cr(III). After allowing Cr(III) and DFOB to react for 5 days to form the complex, reaction rates of Cr(III) with H₂O₂ appear to be lowered probably because of steric hindrance of the chelated Cr(III).     

SERS investigation of possible extraterrestrial life traces: Experimental adsorption of adenine on a Martian meteorite

Abstract– The identification of adenine by surface enhanced Raman scattering (SERS) on different mineral phases of a Martian meteorite Dar al Gani (DaG) 670 has been adopted as a test to verify the capability of this technique to detect trace amounts of organic or biological substances deposited over, or contained in, extraterrestrial materials. Raman spectra of different phases of meteorite (olivine, pyroxene, and ilmenite), representative of Martian basaltic rocks, have been measured by three laser sources with wavelengths at 785, 632.8, and 514.5 nm, coupled to a confocal micro‐Raman apparatus. Adenine deposited on the Martian meteorite cannot be observed in the normal Raman spectra; when, instead, meteorite is treated with silver colloidal nanoparticles, the SERS bands of adenine are strongly enhanced, allowing an easy and simple identification of this nucleobase at subpicogram level.     

A theoretical analysis of the systematic errors in the red clump distance to the Large Magellanic Cloud (LMC)

We present a detailed analysis of the uncertainty on the theoretical population corrections to the Large Magellanic Cloud (LMC) red clump (RC) absolute magnitude, by employing a population synthesis algorithm to simulate theoretically the photometric and spectroscopic properties of RC stars, under various assumptions concerning the LMC star formation rate (SFR) and age–metallicity relationship (AMR). A comparison of the outcome of our simulations with observations of evolved low- to intermediate-mass stars in the LMC allows one to select the combinations of SFR and AMR that bracket the real LMC star formation history, and to estimate the systematic error on the associated RC population corrections.
The most accurate estimate of the LMC distance modulus from the RC method (adopting the OGLE-II reddening maps for the LMC) is obtained from the K -band magnitude, and provides  ( m − M )_0,LMC= 18.47 ± 0.01(random)^+0.05_−0.06(systematic)  . Distances obtained from the I band, or from the multicolour RC technique which determines at the same time reddening and distance, both agree (albeit with a slightly larger error bar) with this value.