Tot Ratio Research Articles

The crystal structure of mineral fibres. 3. Actinolite asbestos

The present work reports chemical and structural data of actinolite asbestos from Aurina Valley, Bolzano (Italy). The chemical composition was determined using EMPA and TG analysis, and the Fe 3+ /Fe tot ratio was accurately evaluated with independent 57 Fe Mossbauer spectroscopy. Morphology and crystallinity were also investigated through SEM and TEM investigations. Crystal structure was refined using high-resolution synchrotron XRPD data. The iron content of Aurina Valley sample is lower compared to two representative asbestiform actinolite samples (with structure refinement) taken from the literature (FeO tot 7.77 wt% against 12÷13 wt%, respectively), accounting for the reduced cell volume here measured (910.29 A. against 912÷918 A., respectively). Refined site scattering values of Aurina Valley sample are in agreement with those calculated from chemical compositions, and the optimized structural formula is: K 0.02 Na 0.05 (Na 0.08 Ca 1.92 ) Ʃ=2.00 (Mg 3.80 Fe 2+0.79 Fe 3+0.11 Al 0.20 Mn 0.05 Ni 0.02 Cr 0.01 ) Ʃ= 4.98 (Si 7.67 Al 0.25 ) Ʃ=7.92 O 21.69 (OH) 2.31 . The C sites M (1), M (2) and M (3) are occupied by Mg and Fe in a proportion of ~4:1, whereas the M (4) site contains mainly Ca and a very small amount of Na. Iron exclusively occupies the octahedral C sites, with Fe 2+ ions occurring at the M (1,2,3) sites and the small amount of Fe 3+ (13% of Fe tot ) ordered at the M (2) site. The refined crystal structure and cation distribution are fully consistent with results previously obtained on asbestiform and non-asbestiform samples belonging to the tremolite-actinolite-ferro– actinolite substitutional series.

Allosteric Sensing of Fatty Acid Binding by NMR: Application to Human Serum Albumin

Human serum albumin (HSA) serves not only as a physiological oncotic pressure regulator and a ligand carrier but also as a biomarker for pathologies ranging from ischemia to diabetes. Moreover, HSA is a biopharmaceutical with a growing repertoire of putative clinical applications from hypovolemia to Alzheimer's disease. A key determinant of the physiological, diagnostic, and therapeutic functions of HSA is the amount of long chain fatty acids (LCFAs) bound to HSA. Here, we propose to utilize (13)C-oleic acid for the NMR-based assessment of albumin-bound LCFA concentration (CONFA). (13)C-Oleic acid primes HSA for a LCFA-dependent allosteric transition that modulates the frequency separation between the two main (13)C NMR peaks of HSA-bound oleic acid (ΔνAB). On the basis of ΔνAB, the overall [(12)C-LCFA]Tot/[HSA]Tot ratio is reproducibly estimated in a manner that is only minimally sensitive to glycation, albumin concentration, or redox potential, unlike other methods to quantify HSA-bound LCFAs such as the albumin-cobalt binding assay.

Models for the estimation of Fe3+/Fetotratio in terrestrial and extraterrestrial alkali- and iron-rich silicate glasses using Raman spectroscopyk

To develop Raman spectroscopy as a quantitative tool in both geosciences and planetary sciences the effect of iron oxidation state (Fe 3+ /Fe tot ) on the Raman spectra of basaltic and pantelleritic glasses has been investigated. We have used remelted pantellerite from Pantelleria Island and synthetic iron-rich basaltic glasses [from Chevrel et al. (2014)]. The Raman spectra of pantelleritic glasses reveal dramatic changes in the high wavelength region of the spectrum (800–1200 cm −1 ) as iron oxidation state changes. In particular the 970 cm −1 band intensity increases with increasing oxidation state of the glass (Fe 3+ /Fe tot ratio from 0.24 to 0.83). In contrast, Raman spectra of the basaltic glasses do not show the same oxidation state sensitivity (Fe 3+ /Fe tot ratio from 0.15 to 0.79). A shift, however, of the 950 cm −1 band to high wavenumber with decreasing iron oxidation state can be observed. We present here two empirical parameterizations (for silica- and alkali-rich pantelleritic glasses and for iron-rich basaltic glasses) to enable estimation of the iron oxidation state of both anhydrous and hydrous silicate glasses (up to 2.4 wt% H 2 O). The validation of the models derived from these parameterizations have been obtained using the independent characterization of these melt samples plus a series of external samples via wet chemistry. The “pantelleritic” model can be applied within SiO 2 , FeO, and alkali content ranges of ~69–75, ~7–9, and ~8–11 wt%, respectively. The “basaltic” model is valid within SiO 2 , FeO, and alkali content ranges of ~42–54, ~10–22, and ~3–6 wt%, respectively. The results of this study contribute to the expansion of the compositionally dependent database previously presented by Di Genova et al. (2015) for Raman spectra of complex silicate glasses. The applications of these models range from microanalysis of silicate glasses (e.g., melt inclusions) to handheld in situ terrestrial field investigations and studies under extreme conditions such as extraterrestrial (i.e., Mars), volcanic, and submarine environments.

Pharmacokinetics, Metabolism, and Excretion of the Antiviral Drug Arbidol in Humans

Arbidol is a broad-spectrum antiviral drug that is used clinically to treat influenza. In this study, the pharmacokinetics, metabolism, and excretion of arbidol were investigated in healthy male Chinese volunteers after a single oral administration of 200 mg of arbidol hydrochloride. A total of 33 arbidol metabolites were identified in human plasma, urine, and feces. The principal biotransformation pathways included sulfoxidation, dimethylamine N-demethylation, glucuronidation, and sulfate conjugation. The major drug-related component in the plasma was sulfinylarbidol (M6-1), followed by unmetabolized arbidol, N-demethylsulfinylarbidol (M5), and sulfonylarbidol (M8). The exposures of M5, M6-1, and M8, as determined by the metabolite-to-parent area under the plasma concentration-time curve from 0 to t (AUC(0-t)) ratio, were 0.9 ± 0.3, 11.5 ± 3.6, and 0.5 ± 0.2, respectively. In human urine, glucuronide and sulfate conjugates were detected as the major metabolites, accounting for 6.3% of the dose excreted within 0 to 96 h after drug administration. The fecal specimens mainly contained the unchanged arbidol, accounting for 32.4% of the dose. Microsomal incubation experiments demonstrated that the liver and intestines were the major organs that metabolize arbidol in humans. CYP3A4 was the major isoform involved in arbidol metabolism, whereas the other P450s and flavin-containing monooxygenases (FMOs) played minor roles. These results indicated possible drug interactions between arbidol and CYP3A4 inhibitors and inducers. Further investigations are needed to understand the importance of M6-1 in the efficacy and safety of arbidol, because of its high plasma exposure and long elimination half-life (25.0 h).

Influence of underwater light fields on pigment characteristics in the Baltic Sea – results of statistical analysis

Changes in phytoplankton pigment concentrations in Case 2 waters (such as those of the Baltic Sea) were analysed in relation to the light intensity and its spectral distribution in the water. The analyses were based on sets of empirical measurements containing two types of data: chlorophyll and carotenoid concentrations obtained by HPLC, and the distribution of underwater light fields measured with a MER 2040 spectrophotometer – collected during 27 research cruises on r/v ‘Oceania’ in 1999–2004. Statistical analysis yielded relationships between the total relative (to chlorophyll a concentrations) concentrations of major groups of phytoplankton pigments and optical depth τ, between the total relative concentrations of major groups of photosynthetic pigments (chlorophylls b (Cchl b tot/Cchl a tot), chlorophylls c (Cchl c tot/Cchl a tot) and photosynthetic carotenoids (CPSC tot/Cchl a tot)) and the spectral fitting function (the ‘chromatic acclimation factor’), and between the total relative concentrations of photoprotective carotenoids (CPPC tot/Cchl a tot) in Baltic waters and the potentially destructive radiation (PDR), defined as the absolute amount of energy in the blue part of the spectrum (400–480nm) absorbed by unit mass of chlorophyll a. The best approximations were obtained for the total chlorophyll c content, while the relative estimation errors were the smallest (σ−=34.6%) for the approximation to optical depth and spectral fitting function. The largest errors related to the approximation of chlorophyll b concentrations: σ−=56.7% with respect to optical depth and 57.3% to the spectral fitting function.A comparative analysis of the relative (to chlorophyll a content) concentrations of the main groups of pigments and the corresponding irradiance characteristics in ocean (Case 1) waters and Baltic waters (Case 2 waters) was also carried out. The distribution of Cchl b tot/Cchl a tot ratios with respect to optical depth reveals a decreasing trend with increasing τ for Baltic data, which is characteristic of photoprotective pigments and the reverse of the trend in oceans. In the case of the Cchl c tot approximations, the logarithmic statistical error is lower for Baltic waters than for Case 1 waters: σ−=34.6% for Baltic data and σ−=39.4% for ocean data. In relation to photoprotective carotenoids (CPPC), σ− takes a value of 38.4% for Baltic waters and 36.1% for ocean waters. The relative errors of the approximated concentrations of different pigment groups are larger than those obtained for ocean waters. The only exception is chlorophyll c, for which the logarithmic statistical error is about 8.8% lower (σ−=34.6% for Baltic waters and 38.2% for ocean waters). Analysis of the errors resulting from the approximations of the photoprotective carotenoid content, depending on the energy characteristics of the underwater irradiance in the short-range part of PAR, showed that the relative errors are 1.3 times higher for Baltic waters than for ocean waters: σ−=38.4% for Baltic waters and 32.0% for ocean waters.

Effects of Phanerochaete chrysosporium on biologic activity of soil amended with olive mill wastewaters

Effects of the untreated olive mill wastewater (UOMW) and the bioaugmented olive mill wastewater (BOMW) with the fungus Phanerochaete chrysosporium (P. chrysosporium ) for the amendment of soil were investigated. Results showed that UOMW inhibited the soil respirometric activity, while BOMW exhibited significantly higher respiration levels compared to the unamended and the UOMW amended soils. The ratio of C-CO 2/C tot decreased from 6.7 in the unamended soil to 6.34, to 2.74 and to 1.6 in soils amended consecutively with 50, 100 and 200 m 3 ha -1 of UOMW. Based on the first results, the UOMW dose of 50 m 3 ha -1 showed the elevated C-CO 2/C tot ratio in comparison with the two other doses (100 and 200 m 3 ha -1 ) so that it was chosen to test the effects of its bioaugmentation with P. chrysosporium on the soil biodegradation activities. The fungus P. chrysosporium was added at three different forms; spores suspension (10 6 spores g -1 ), mycelium form (cultivated in liquid medium) and colony form (mycelium fragments from solid medium).The soil amended with 50 m 3 ha -1 of BOMW showed higher CCO 2/C tot ratio in comparison with control soil (unamended) and with soil amended with 50 m 3 ha -1 of

Influence of γ-radiation on the reactivity of montmorillonite towards H 2O 2

Compacted and water saturated bentonite will be used as an engineered barrier in deep geological repositories for radioactive waste in many countries. Due to the high dose rate of ionizing radiation outside the canisters holding the nuclear waste, radiolysis of the interlayer and pore water in the compacted bentonite is unavoidable. Upon reaction with the oxidizing and reducing species formed by water radiolysis (OH •, e − (aq), H •, H 2O 2, H 2, HO 2 •, H 3O +), the overall redox properties in the bentonite barrier may change. In this study the influence of γ-radiation on the structural Fe(II)/Fe Tot ratio in montmorillonite and its reactivity towards hydrogen peroxide (H 2O 2) was investigated in parallel experiments. The results show that under anoxic conditions the structural Fe(II)/Fe Tot ratio of dispersed Montmorillonite increased from ≤3 to 25–30% after γ-doses comparable to repository conditions. Furthermore, a strong correlation between the structural Fe(II)/Fe Tot ratio and the H 2O 2 decomposition rate in montmorillonite dispersions was found. This correlation was further verified in experiments with consecutive H 2O 2 additions, since the structural Fe(II)/Fe Tot ratio was seen to decrease concordantly. This work shows that the structural iron in montmorillonite could be a sink for one of the major oxidants formed upon water radiolysis in the bentonite barrier, H 2O 2.

Physical properties of lead iron phosphate glasses containing Cr 2O 3

The influence of Cr 2O 3 on glass forming characteristics and physical properties of PbO–Fe 2O 3–P 2O 5 glasses has been investigated by Raman and Mössbauer spectroscopies, X-ray diffraction analysis (XRD), Differential Thermal Analysis (DTA), Scanning Electron Microscopy (SEM) and impedance spectroscopy. Glasses of the general composition xCr 2O 3–(28.3-x)PbO–28.7Fe 2O 3–43.0P 2O 5, 0 ≤ × ≤ 10, (mol%) were prepared by conventional melt-quenching technique. The compositions containing up to 4 mol% Cr 2O 3 formed fully amorphous samples and their Raman spectra show systematic increase in the fraction of orthophosphate Q 0 units with increasing Cr 2O 3 content and O/P ratio. On the other hand, compositions containing 8 and 10 mol% Cr 2O 3 partially crystallized during cooling and annealing to Fe 7(PO 4) 6, Fe 2Pb 3(PO 4) 4 and Cr 2Pb 3(PO 4) 4. A high tendency for crystallization of these melts is related to the high O/P (> 4) and Fe 2+/Fe tot (≈ 0.60) ratios. Electrical conductivity of xCr 2O 3–(28.3-x)PbO–28.7Fe 2O 3–43.0P 2O 5, 0 ≤ × ≤ 10, (mol%) compositions is independent of Cr 2O 3 and controlled entirely by the polaron transfer between Fe 2+ and Fe 3+ ions.

Synthesis and Mössbauer characterization of Fe 1+x Cr 2-x O 4 (0 ≤ x ≤ 2/3) spinel single crystals

Periodico di Mineralogia (2011), 80, 1 (Special Issue), 39-55 - DOI: 10.2451/2011PM0004 Special Issue in memory of Sergio Lucchesi Synthesis and Mossbauer characterization of Fe 1+x Cr 2-x O 4 (0 ≤ x ≤ 2/3) spinel single crystals Marco Quintiliani 1 , Giovanni B. Andreozzi 1,* and Henrik Skogby 2 1 Dipartimento di Scienze della Terra, Sapienza Universita di Roma, Italy 2 Department of Mineralogy, Swedish Museum of Natural History, Stockholm, Sweden *Corresponding author: gianni.andreozzi@uniroma1.it Abstract Spinel single crystals belonging to the FeCr 2 O 4- Fe 3 O 4 join were synthesized by a flux growth method (Na 2 B 4 O 7 as flux, temperature range of 1200-900 °C and cooling rate of 4 °C/h). Crystals with compositions corresponding to Fe 1+x Cr 2-x O 4 (0 ≤ x ≤ 2/3) were obtained and successively investigated by a combined microchemical, diffractometric and spectroscopic approach. Fe-Cr-spinel single crystals produced are of different quality (in terms of size and shape). The flux content in the starting mixture showed to have the most relevant influence on the quality of synthetic products. Electron microprobe analysis evidenced a chemical heterogeneity for crystals of the same batch, with small crystals (down to 50 μm) being more homogeneous than the large ones. Mossbauer spectroscopy was used to determine the actual Fe 3+ /Fe tot ratios and highlighted the absence of magnetic phases. The combined chemical and spectroscopic approach allowed to exclude any deviation from stoichiometry due to oxidation. In contrast with most of the existing literature, Mossbauer spectroscopy indicated the Fe 2.5+ valence state to be present even for iron poor samples with composition close to the end member chromite. Key words : chromite-magnetite solid solution; synthesis, spinel single crystals; Mossbauer spectroscopy.

Progressive palaeoenvironmental change during the Late Barremian–Early Aptian as prelude to Oceanic Anoxic Event 1a: Evidence from the Gorgo a Cerbara section (Umbria-Marche basin, central Italy)

During Oceanic Anoxic Event 1a (OAE 1a, 120 Ma; Li et al., 2008), organic carbon-rich layers were deposited in marine environments under anoxic conditions on a global scale. In this study, palaeoenvironmental conditions leading to this event are characterised by studying the Upper Barremian to the Lower Aptian succession of the Gorgo a Cerbara section (central Italy). For this, an integrated multi-proxy approach (δ 13C carb; δ 13C org; δ 18O; phosphorus; Total Organic Carbon, TOC; bulk-rock mineralogy, as well as redox-sensitive trace elements — RSTEs) has been applied. During the Late Barremian, thin organic-rich layers occur episodically, and associated C org:P tot ratios indicate the presence of intermittent dysoxic to anoxic conditions. Coarse correlations are observed between TOC, P and biogenic silica contents, indicating links between P availability, productivity, and TOC preservation. However, the corresponding δ 13C carb and δ 18O records remain quite stable, indicating that these brief periods of enhanced TOC preservation did not have sufficient impact on the marine carbon reservoir to deviate δ 13C records. Around the Barremian–Aptian boundary, TOC-enriched layers become more frequent. These layers correlate with negative excursions in the δ 13C carb and δ 13C org records, possibly due to a warming period as indicated by the δ 18O record. During the earliest Aptian, this warming trend is reverted into a cooling trend, which is then followed by an important warming step near the onset of Oceanic Anoxic Event 1a (OAE 1a). During this time period, organic-rich intervals occur, which are characterised by the progressive increase in RSTE. The warming step prior the onset of OAE 1a is associated with the well-known negative spike in δ 13C carb and δ 13C org records, an important peak in P accumulation, RSTE enrichments and C org:P tot ratios indicating the prevalence of anoxic conditions. The Selli Level itself may document a cooling phase. RSTE enrichments and C org:P tot ratios confirm the importance of anoxic conditions during OAE 1a at this site. The Gorgo a Cerbara section is interpreted to reflect the progressive impact of palaeoenvironmental change related to the formation of the Ontong-Java plate-basalt plateau, which started already around the Barremian–Aptian boundary and culminated into OAE 1a.

Electrical properties of Cr 2O 3–Fe 2O 3–P 2O 5 glasses. Part II

The electrical properties of xCr 2O 3–(40−x)Fe 2O 3–60P 2O 5, 0 ≤ x ≤ 10, (mol%) glasses have been investigated by impedance spectroscopy. In the glasses containing up to ~ 5 mol% Cr 2O 3, electrical conductivity increases due to the increase in the Fe 2+/Fe tot ratio. The conduction in these glasses is independent on Cr 2O 3 and it is controlled by the polaron hopping between iron ions. The electrical conductivity of the partially crystallized sample with 10 mol% Cr 2O 3 slightly increases although the Fe 2O 3 content and the fraction of Fe 2+ ions are smaller. This effect is related to the formation of highly disruptive regions around the β-CrPO 4 and Fe 3(P 2O 7) 2 crystallites in the glass matrix of this sample. These interconnected disruptive regions form the easy conductive pathways leading to a higher conductivity. Changes in the dielectric permittivity in chromium iron phosphate glasses are dependent on the Fe 2+/Fe tot ratio and, therefore, associated with the concentration of polarons related to Fe 2+ and Fe 3+ sites.

Sedimentary organic carbon to phosphorus ratios as a redox proxy in Quaternary records from the Mediterranean

In this study, organic carbon to organic phosphorus (C org/P org) and total phosphorus (C org/P tot) ratios as bottom water redox proxies are explored for two eastern Mediterranean sediment records extending back ~ 600–700 kyrs. Cores KC19C (19.6 m long, 2750 m water depth) and KC01B (37.0 m long, 3643 m water depth) contain numerous organic-rich layers (sapropels). Throughout the two cores, variations found in the C org/P ratios correspond to those for other redox proxies such as total S contents and V/Al ratios. Accordingly, these are interpreted as variations in bottom water oxygenation and inter-sapropel redox variability. In core KC19C, the original C org/P signals seem to have been preserved despite intense post-depositional sulfidization. High-resolution P fractionation data of sapropel S5 from a third core (PS25PC, 3304 m water depth) showing high and relatively stable C org/P org ratios, indicate that sapropel S5 at this deep location was deposited under permanently reducing conditions. While P regeneration from organic matter was intense, net P burial increased in the sapropel due to enhanced burial of inorganic calcium phosphate, likely biogenic Ca–P. Sediment P contents and C org/P tot ratios in S5 are variable, reflecting short-term changes in marine conditions (productivity/redox) and sediment chemistry. The C org/P org and C org/P tot ratios thus provide valuable insight into paleoceanographic conditions and pathways of P cycling for (Mediterranean) sediment records extending back at least ~ 600–700 kyrs.

Detailed crystal chemistry and iron topochemistry of asbestos occurring in its natural setting: A first step to understanding its chemical reactivity

Five samples of tremolite asbestos from Italy and USA were fully characterized by ICP-MS, SEM, EMPA, FT-IR, MS, XRPD, to correlate crystal chemistry with chemical reactivity. Iron topochemistry was investigated in detail, due to the role of Fe in the aetiology of respiratory inflammatory diseases. The Italian tremolite samples have different Fe contents (San Mango > Ala di Stura > Rufeno > Castelluccio Superiore), and the USA sample from Maryland shows a value almost double that of the Italian samples. The bulk Fe 3+/Fe tot ratio was quantified by Mössbauer spectroscopy, and the values obtained range from 6% Fe tot (San Mango tremolite) to 24% Fe tot (Mt. Rufeno tremolite). A possible site distribution of Fe was derived from combining chemical, spectroscopic (Mössbauer) and structural (Rietveld refinement) data. For all samples Fe 2+ was disordered over M(1), M(2) and M(3) sites, whereas Fe 3+ was allocated to M(2). Production of HO° radical in the presence of hydrogen peroxide from the Italian samples is a measure of chemical reactivity, with the lowest value observed for the Castelluccio Superiore sample, and the highest value for the San Mango sample. Notably, HO° radical production is directly related to the Fe occupancy of the M(1) and M(2) octahedra, which are more exposed on the external surface of the fibers than M(3) octahedra and therefore have higher probability of being involved in surface reactions.

Sedimentary organic matter characterization of the Triassic–Jurassic boundary GSSP at Kuhjoch (Austria)

The Triassic–Jurassic (T–J) boundary interval coincides with enhanced extinction rates in the marine realm and pronounced changes in terrestrial ecosystems on the continents. It is further marked by distinct negative excursions in the δ 13C org and δ 13C carb signature that may represent strong perturbations of the global carbon cycle. We present integrated geochemical, stable-isotope and palynological data from the Kuhjoch section, the Global boundary Stratotype Section and Point (GSSP) for the base of the Jurassic (Northern Calcareous Alps, Austria). We show that the initial carbon isotope excursion (CIE), coinciding with the marine extinction interval and the formation of black shales in the western Tethys Eiberg Basin, is marked by only minor changes in kerogen type, which is mainly of terrestrial origin. Increased Total Organic Carbon (TOC) concentrations of 9% at the first half of the initial CIE coincide with Hydrogen Index (HI) values of over 600 mg HC/g TOC. The high correlation (with R 2 = 0.93) between HI values and terrestrial Cheirolepidiaceaen conifer pollen suggests a terrestrial source for the hydrogen enriched organic compounds. The lack of major changes in source of the sedimentary organic matter suggests that changes in the δ 13C org composition are genuine and represent true disturbances of the global C-cycle. The sudden decrease in total inorganic carbon (TIC) concentrations likely represents the onset of a biocalcification crisis. It coincides with a 4.5‰ negative shift in δ 13C org values and possibly corresponds to the onset of CAMP related volcanic activity. The second half of the initial CIE is marked by the dramatic increase of green algae remains in the sediment. The simultaneous increase of the C org/N tot ratio suggests increased marine primary production at the final stage of black shale formation.

Structural and spectroscopic characterization of a suite of fibrous amphiboles with high environmental and health relevance from Biancavilla (Sicily, Italy)

This study reports new spectroscopic and structural data of fibrous amphiboles from the volcanic area of Biancavilla (Sicily, Italy) that generated interest because of an anomalous increase of pleural mesothelioma of inhabitants. Each of the four samples is made of loose fibers, which show an edenite-winchite (fluorine) compositional trend, with significant tremolite component. Small amounts of iron (3.6–6.0 wt% FeO tot ) were identified in all samples, and the Fe 3+ /Fe tot ratios were evaluated by Mossbauer spectroscopy: two samples are characterized by Fe 3+ /Fe tot ratios between 50 and 70%, and the other two have Fe 3+ /Fe tot ratios higher than 90%. The OH-stretching region was investigated by FTIR, and no absorption bands were observed. Structural investigation was carried out by X-ray powder diffraction using the Rietveld method. Cell parameters, positional parameters for all the atoms, and site scattering for M1, M2, M3, M4, A, and A( m ) were refined. The most important differences with respect to prismatic fluoro-edenite are the decrease of β, a , and c with decreasing Ca content, A-site occupancy, and tetrahedral Al content, respectively. By combining chemical, spectroscopic, and structural data, possible site occupancies were obtained. In particular, it was found that Fe 2+ is distributed between M1 and M2 sites; moreover, for the two samples enriched in Fe 2+ , it is also present at M4. Fe 3+ is generally ordered at M2 site; however, for the two samples enriched in Fe 3+ , minor amounts are partially disordered between M1 and M3 sites. For the Biancavilla amphibole fibers, the large compositional variation observed in every sample makes the classification very difficult, so that the regulatory agencies would not classify as “asbestos” the whole mineral series, because of the large components of edenite and winchite in addition to tremolite. Many common features were found with respect to amphibole fibers from Libby, Montana, including Fe contents and oxidation state. Preliminary results of in vitro toxicological tests on Biancavilla fibers confirmed their high reactivity, and suggest that the samples with the highest Fe 2+ contents induce a rapid start to cell mortality.

Mercury content and speciation in the Phlegrean Fields volcanic complex: Evidence from hydrothermal system and fumaroles

Mercury is outstanding among the global environmental pollutants of continuing concern. Although degassing of active volcanic areas represents an important natural source of mercury into the atmosphere, still little is known about the amount and behaviour of Hg in volcanic aquifers, especially regarding its chemical speciation. In order to assess the importance of mercury emissions from active volcanoes, thermal waters were sampled in the area surrounding La Solfatara, Pozzuoli bay. This is the most active zone of the Phlegrean Fields complex (coastal area north–west of Naples), with intense hydrothermal activity at present day. Studied groundwaters show total Hg (THg) concentrations range from 56 to 171 ng/l and are lower than the 1000 ng/l threshold value for human health protection fixed by the World Health Organization (WHO, 1993). We also carefully discriminated the different aqueous species of Hg in the collected water samples. Besides, original data on Hg determination in gaseous manifestations at La Solfatara crater are also reported. We measured volcanogenic mercury concentration and Hg/S tot ratio both in the volcanic plume and in fumarolic condensates in order to better constrain Hg reactivity once emitted into the atmosphere. Data on Hg/S tot reveal that there is no significant difference between Hg volcanic composition at the venting source (fumaroles) and in near-vent diluted volcanic plumes (1.6 × 10 − 5 and 1.9 × 10 − 5 , respectively), suggesting that there is limited Hg chemical processing in volcanic fumarole plumes, at least on the timescales of a few seconds investigated here. Combining the mean fumaroles Hg/CO 2 mass ratio of about 1.3 × 10 − 8 (molar ratio: 2.1 × 10 − 9 ) with the hydrothermal soil diffuse CO 2 degassing of the area, the annual Hg flux from La Solfatara is estimated as 7 kg y − 1 (0.007 t y − 1 ). Current mercury emission from La Solfatara volcano represents a very small contribution to the estimated global volcanic budget for this element, and the estimated Hg flux is considerably lower than that estimated from open-conduit active basaltic volcanoes.

Origin and fate of particulate organic matter in the southern Beaufort Sea – Amundsen Gulf region, Canadian Arctic

To establish the relative importance of terrigenous and marine organic matter in the southern Beaufort Sea, we measured the concentrations and the stable isotopic compositions of organic carbon and total nitrogen in sediments and in settling particles intercepted by sediment traps. The organic carbon content of surface sediment in the Chukchi and southern Beaufort Seas ranged from 0.6 to 1.6% dry wt., without a clear geographical pattern. The C ORG:N TOT ratio ranged from 7.0 to 10.4 and did not vary significantly downcore at any one station. Values of δ 13C ORG and δ 15N TOT in the sediment samples were strongly correlated, with the highest values, indicative of a more marine contribution, in the Amundsen Gulf. In contrast, the organic matter content, elemental (C ORG:N TOT ratio) and isotopic ( δ 13C ORG and δ 15N TOT) composition of the settling particles was different from and much more variable than in the bottom sediments. The isotopic signature of organic matter in the Beaufort Sea is well constrained by three distinct end-members: a labile marine component produced in situ by planktonic organisms, a refractory marine component, the end product of respiration and diagenesis, and a refractory terrigenous component. A three-component mixing model explains the scatter observed in the stable isotope signatures of the sediment trap samples and accommodates an apparent two-component mixing model of the organic matter in sediments. The suspended matter in the water column contains organic matter varying from essentially labile and marine to mostly refractory and terrigenous. As it settles through the water column, the labile marine organic matter is degraded, and its original stable isotope signature changes towards the signature of the marine refractory component. This process continues in the bottom sediment with the result that the sedimentary organic matter becomes dominated by the refractory terrigenous and marine components.

From structure topology to chemical composition. VII. Titanium silicates: the crystal structure and crystal chemistry of jinshajiangite

The crystal structure of jinshajiangite, ideally BaNaTi 2 Fe 4 2+ (Si 2 O 7 ) 2 O 2 (OH) 2 F, a 10.6785(8), b 13.786(1), c 20.700(2) A, β 94.937(1)°, V 3035.93(6) A 3 , sp. gr. C 2/ m , Z = 8, D calc. 3.767 g/cm 3 , from Norra Karr, Tonkoping province, Sweden, has been refined to R 1 5.69 % on the basis of 3193 unique reflections (F O > 4σF). Electron microprobe analysis gave (wt%): SiO 2 27.56, Nb 2 O 5 0.12, TiO 2 18.36, ZrO 2 0.51, FeO 23.42, Fe 2 O 3 2.89 [the Fe 3+ /Fe tot ratio of 0.10(9) was determined by Mossbauer spectroscopy], MnO 5.13, MgO 0.44, CaO 2.52, BaO 10.24, K 2 O 1.95, Na 2 O 2.27, F 2.33, H 2 O 2.00 (calc. from structure refinement: OH + F = 3 apfu ), O = F − 0.98, total 98.76. The empirical formula is (Ba 0.58 K 0.36 ) ∑0.94 (Na 0.57 Ca 0.39 ) ∑0.96 (Fe 2.84 2+ Mn 0.63 Fe 0.32 3+ Mg 0.10 Zr 0.04 Na 0.07 ) ∑4.00 (Ti 2.00 Nb 0.01 ) ∑2.01 (Si 2 O 7 ) 2 O 2.12 (OH) 1.93 F 1.07 , calculated on the basis of 4 Si apfu . The crystal structure of jinshajiangite can be described as a combination of a TS block and an I block. The TS (titanium silicate) block consists of HOH sheets (H-heteropolyhedral, O-octahedral), and is a component of 27 Ti-disilicate minerals. In the O sheet, there are five [6]-coordinated M O sites occupied mainly by Fe 2+ and Mn 2+ , with minor Fe 3+ , Mg, Zr and Na with O –O> = 2.175 A. Five M O sites give ideally Fe 2+ 4 pfu . In the H sheet, there are three [6]-coordinated M H sites occupied solely by Ti (Ti = 2 apfu ), with H –O>. = 1.953 A, and four [4]-coordinated Si sites occupied solely by Si, with . = 1.619 A. The M H octahedra and (Si 2 O 7 ) groups constitute the H sheet. Linkage of H and O sheets via common vertices of M H octahedra and (Si 2 O 7 ) groups with M O (1–5) octahedra results in a TS block. The topology of the TS block is as in Group II of the Ti disilicates (Ti = 2 apfu ). There are six interstitial sites, three [9–10]-coordinated Ba-dominant A P sites with P –O> = 2.98 A and three [10]-coordinated Na-dominant B P sites with P –O> = 2.600 A. The total content of three A P sites sums to ~1 apfu = Ba 0.58 K 0.36 or ideally 1 Ba pfu . The total content of the three B P sites is Na 0.57 Ca 0.39 or ideally 1 Na pfu . Along c , the TS blocks link via common vertices of M H octahedra (as in astrophyllite-group minerals) and A P and B P sites which constitute the I block. Jinshajiangite is an Fe 2+ analogue of perraultite, ideally BaNaTi 2 Mn 4 2+ (Si 2 O 7 ) 2 O 2 (OH) 2 F, and its crystal structure is topologically identical to that of perraultite.

Sedimentary record of anthropogenic contaminants (trace metals and PAHs) and organic matter in a Mediterranean coastal area (Gulf of Palermo, Italy)

The Gulf of Palermo (Italy, Mediterranean Sea) is a contaminated coastal environment with a relatively high influx of unregulated industrial and domestic effluents. Two sediment box-cores were collected at water depths of 100 and 712 m. Samples were analysed for trace metals (As, Cu, Hg, Mn, Ni, Pb), total polycyclic aromatic hydrocarbons (ΣPAHs), organic carbon to total nitrogen (C org/N tot) ratios and organic carbon and nitrogen isotopic composition ( δ 13C org and δ 15N tot). At the coastal site, trace metal and ΣPAH depth profiles show a clear upcore increase, indicating increasing contamination over the recent past. Concentrations of ΣPAHs, Hg, Pb, Cu, and As appear to be potentially hazardous, far exceeding national and international regulatory guidelines. C org/N tot ratios and δ 13C org indicate the marine origin of organic matter, supporting eutrophication rather than direct land runoff as principal carbon source. The distal site exhibits lesser contaminant input and minor anthropogenic influence. On the whole, sedimentary records were reliable indicators of recent metal and ΣPAH contamination and organic enrichment.

Dependence of slip weakening distance (Dc) on final slip during dynamic rupture of earthquakes

SUMMARY In this study, we aim to understand the dependence of the critical slip weakening distance (D c) on the final slip (D tot) during the propagation of a dynamic rupture and the consistency of their inferred correlation. To achieve this goal we have performed a series of numerical tests suitably designed to validate the adopted numerical procedure and to verify the actual capability in measuring D c. We have retrieved two kinematic rupture histories from spontaneous dynamic rupture models governed by a slip weakening law in which a constant D c distribution on the fault plane as well as a constant D c/D tot ratio are assumed, respectively. The slip velocity and the shear traction time histories represent the synthetic ‘real’ target data which we aim to reproduce. We use a 3-D traction-at-split nodes numerical procedure to image the dynamic traction evolution by assuming our modelled slip velocity as a boundary condition on the fault plane. We assume a regularized Yoffe function as source time function in our modelling attempts and we measure the critical slip weakening distance from the inferred traction versus slip curves at each point on the fault. We compare the inferred values with those of the target dynamic models. Our numerical tests show that fitting the slip velocity functions of the target models at each point on the fault plane is not enough to retrieve good traction evolution curves and to obtain reliable measures of D c. We find that the estimation of D c is very sensitive to any small variation of the slip velocity function. An artificial correlation between D c/D tot is obtained when a fixed shape of slip velocity is assumed on the fault (i.e. constant rise time and constant time for positive acceleration) which differs from that of the target model. We point out that the estimation of fracture energy (breakdown work) on the fault is not affected by biases in measuring D c.