1,721,024 research outputs found
Quantitative chemical analysis of erionite fibres using a micro-analytical SEM-EDX method
No full textThe quantitative chemical composition of a sample of erionite-Na from Rome, Oregon (USA) was retrieved by SEM-EDX standardless analysis. The analysed fibres have a diameter commonly smaller than 3 μm, i.e. those more easily inhalable, therefore representing a typical case encountered during environmental investigations. The claimed dependence of the toxicity and biological activity of the fibres to their crystal chemical features renders the reliable chemical characterization of paramount importance. To reduce the errors induced by particle size/morphology effects, an empirical procedure was adopted. In particular, correction factors were calculated for each oxide as a function of the particle diameter using shards of zeolites and feldspathoids of known bulk composition. Those correction factors have to be considered as sample specific. Experimental conditions were optimised in order to minimize the effect of alkali metal migration. Results indicate that particle effects cause on the oxide concentrations a relative underestimation of Al2O3 and K2O by up to ca. 10 %, whereas Na2O is overestimated by up to ca. 15 %. Moreover, the SiO2 concentration is independent from dimension even in the case of very small particles. Finally, comparison between electron-microprobe and SEM-EDX bulk analyses of crystals pointed out a relative underestimation of Na, K, (of ca. 10-15 %) and Ca (of ca. 5 %) for the SEM data, in good agreement with reference structural investigations
Crystal-chemistry and reactivity of fibrous amphiboles of environmental and health interest
No full textLa caratterizzazione cristallochimica di fibre minerali, in particolar modo di anfiboli fibrosi, risulta di grande interesse, non solo per l’aspetto mineralogico, ma anche e soprattutto per quello ambientale e sanitario.
I minerali fibrosi si presentano nelle rocce ospiti solitamente associati in fasci più o meno compatti, anche se in alcuni casi possono presentarsi sciolti nei materiali geologici, come per es. nel recente rinvenimento dell’anfibolo fluoro-edenite nei prodotti vulcanici di Biancavilla, CT, nei quali il minerale fibroso si presenta disperso nel materiale fine che lo ospita, e dal quale risulta alquanto difficoltosa la sua estrazione e separazione, necessaria per le successive analisi mineralogiche (Gianfagna et al., 2003; Gianfagna et al., 2007).
Recenti studi a carattere ambientale, epidemiologico e tossicologico nell’area di Biancavilla hanno evidenziato che l’interazione tra la fibra minerale e l’ambiente organico è risultata strettamente correlata sia alla forma che alla cristallochimica delle fibre anfiboliche che entrano in contatto con il mezzo biologico (Paoletti et al., 2000; Comba et al., 2003; Soffritti et al. 2004).
Anche se in questi ultimi anni particolare attenzione è stata rivolta alla cristallochimica degli anfiboli, sia prismatici che fibrosi, le difficoltà oggettive esistenti per lo studio mineralogico e strutturale delle varietà fibrose non hanno permesso di ottenere ad oggi una loro completa e dettagliata definizione in termini cristallochimici.
Il presente dottorato di ricerca si prefigge quindi di studiare dal punto di vista mineralogico e cristallochimico le varietà fibrose di alcuni anfiboli presenti per la maggior parte in aree in cui si è manifestata maggiormente in passato ed è tutt’ora presente, la problematica di inquinamento ambientale da esposizione naturale a fibre.The present study is devoted to the investigation of amphibole fibers by means of a well tested
multi-analytical approach. The studied speciments are tremolite fibers from ophiolitic outcrops at
different Italian localities such as (from north to south): 1) Ala di Stura (Lanzo Valley, Piedmont);
2) Mt. Rufeno (Acquapendente, Latium); 3) Castelluccio Superiore (Potenza, Basilicata); 4) S.
Mango (Catanzaro, Calabria). A sample of fibrous tremolite from the ophiolite complex
outcropping in Montgomery County, Maryland (USA) was also studied. In addition, the nonregulated
fibrous amphiboles from Biancavilla (Catania, Sicily) and Libby (Montana, USA) are
studied for comparison. The detailed crystal chemical characterization was carried out by
combining Inductively Coupled Plasma-Mass (ICP-MS) spectrometry, Electron Microprobe
Analysis (EMPA), Scanning Electron Microscopy (SEM) with microanalysis system, parallel-beam
X-Ray Powder Diffraction (XRPD), 57Fe Mössbauer spectroscopy (MS) and Fourier-Trasform
Infra-Red (FT-IR) spectroscopy. Beside the mineralogical characterization, the surface chemistry
and surface reactivity of some samples have been also investigated. The surface chemistry of the
fibers was studied by X-Ray Photoelectron Spectroscopy (XPS) with specific attention to the
surface iron content and its oxidation state. Electron Paramagnetic Resonance (EPR) Spectroscopy
was used to characterize the HO° hydroxyl radicals and the measurement of their absolute
concentration. In addition, tests of lipid peroxidation in the presence of hydrogen peroxide were
performed to identify and distinguish their reactivity, and the degradation of linolenic acid in
conditions similar to those found in pulmonary alveoli was monitored. The products of degradation
of linolenic acid were studied by UV-visible spectroscopy. The surface chemistry and the reactivity
of a sample of crocidolite UICC (Union Internationale contre le Cancer, Johannesburg, South
Africa) and a sample of calcite (Iceland spar variety) were also investigated as positive and negative
references, respectively. Finally, full characterization of fibrous amphiboles (morphology, crystal
chemistry, crystal structure, cation site partitioning, Fe3+/Fetot ratio of the bulk and surface, surface
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chemistry and reactivity) was coupled with cytotoxicity tests in vitro (MTT test on A 559 and MeT-
5A cells) performed on the same samples. The aim is to better understand the relationships between
mineralogical features and biological activity in order to shed new light on the chemical, molecular
and toxic-chemical processes in the interaction between fiber and organic environment. This work
required the use of several complementary disciplines from mineralogy to chemistry and biology.
Therefore, the collaboration between the Sapienza University of Rome and the University of Pierre
et Marie Curie of Paris VI was the underlying framework of such a challenging and
interdisciplinary work
Erionite-Na upon heating. Dehydration dynamics and exchangeable cations mobility
Full text linkErionite is a fibrous zeolite significantly more tumorigenic than crocidolite asbestos upon inhalation. In recent years, several papers have been published aimed at characterizing from the crystal-chemical point of view erionite fibres. As their toxicity has been ascribed to Fe acquired within the human body, studies aimed at characterizing the iron topochemistry have also been published, suggesting a possible important role played by the ionic exchange properties and cations mobility of this zeolite on developing carcinogenicity. Here we report the analysis results of the thermal behaviour of erionite-Na, which has been found to deviate significantly from that of erionite-K. This result is in contrast with the current scientific view that differences in weighted ionic potential, Si/Al ratio and size of exchangeable cations result in significantly different thermal behaviours, all those parameters being nearly identical or very similar in both species. The different mobility of the extraframework cations observed in erionite samples with dissimilar chemistry is of particular interest within the frame of the hypothesis that their biological activity could depend, apart from surface interactions, also on bulk effects
Chemical and structural characterization of fibrous richterite with high environmental and health relevance from Libby, Montana (USA)
Full text linkThis study reports new structural and spectroscopic data of a sample of fibrous richterite from Libby, Montana (USA). The OH-stretching region was investigated by FT-IR. The spectrum showed, except for the typical absorption band at 3671 cm-1 assigned to the vibration of the O-H dipole bonded to three [6]Mg cations, a well developed band at 3658 cm-1 attributed to the M(1)+M(3)Fe2+ environment. The M(1)+M(3)Fe2+ occupancy calculated using the FT-IR data is in very good agreement with that obtained combining Mössbauer and EMP data. Fe3+ was only assigned at M(2) owing to the absence in FT-IR spectrum of absorption bands at Δ=-50 cm-1 from the tremolite reference band. Structural investigation was done by X-ray powder-diffraction using the Rietveld method. Cell parameters, fractional coordinates for all non-hydrogen atoms, and site scattering for M(1), M(2), M(3), M(4) and A were refined. The most relevant difference with respect to prismatic winchite is a general reduction of the cell parameters that is ascribed mainly to the higher fluorine content of fibrous richterite. Possible site occupancies were obtained by combining chemical data and Rietveld refinement results
New structural and chemical data of woolly erionite from Oregon
No full textErionite is a naturally occurring fibrous mineral belonging to the ABC-6 family (Gottardi and Galli, 1985). It is well known that exposure to erionite fibers has severe effects on human health. In fact, it has been recognized as a Group-I carcinogen for humans (IARC, 1997) by both the International Agency for Research on Cancer (IARC) and the World Health Organization (WHO). Despite of being a nominally Fe-free phase, several chemical analyses on natural eriontes report a Fe2O3 content up to 3 wt.%. Similarly to amphibole asbestos, erionite toxicity has been partly ascribed to the presence of iron eventually participating to Fenton chemistry and inducing genotoxic damages. Ballirano et al. (2009) carried out a combined spectroscopic and crystal chemical investigation of erione- K from Rome, Oregon. They demonstrated, from Mössbauer spectroscopy, that the small amount of iron oxide was occurring as nanoparticles locate at the surface of the zeolite with dimensions ranging from 1 to 9 nm. Parallel investigations on samples from different localities are currently in progress and preliminary results are the object of the present work.In particular, we report the crystal chemical characterization of an erionite sample from Durkee, Oregon (sample provided by the Smithsonian Institution, Washington) to be used as the starting point for a toxicity investigation. The sample, consisting of woolly bundles of fibres, has been analyzed by XRPD, SEM-EDS and FE-SEM. XRPD data, collected in parallel-beam, transmission geometry, were evaluated by the Rietveld method using the TOPAS (Bruker AXS, 2009) crystallographic software running in launch-mode. The strong anisotropic shape of the crys- tallites resulted in a diffraction-vector-dependent broadening of diffraction maxima that was modelled applying the ellipsoid-model approach of Katerinopoulou et al. (2012). A significant improvement of the fit was obtained as compared to the use of an isotropic shape of crystallites.Refined cell parameters are a = 13.2360(5) Å and c = 15.0671(6) Å. Evaluation of the mean tetrahedral bond distances clearly indicates a preferential partition of Al on T2 site. Extraframework (EF) cations were allocated at the K1 site, located at the centre of the ε-cage [4665], and in three Ca1, Ca2, and Ca3 located within the erionite cage [4126586]. A further cationic site K2 was found at the centre of the boat-shaped 8-member rings (8MR) forming the walls of the erionite cage, as firstly reported by Schlenker et al. (1977) for a dehydrated erionite sample. The ellipsoid radii are of ra = 153.1(15) nm and rc = 864(53) nm with a rc/ra ratio of 5.7(9). Preliminary semi-quantitative chemical analysis of the bundles pointed out to a variable Fe2O3 content of ca. 2-4 wt.% and the presence of Ca, Mg, Na and K as EF cations. However, detailed SEM analyses, carried out on dispersed fibres, clearly indicated the absence of both calcium and iron.The reliability of the crystal chemistries of the new set of analyses has been evaluated using both the balance error formula (E%) and the Mg-contenttest (Dogan and Dogan, 2008). Up to 60% of analyses passed both the E% and Mg-content tests. The final mean crystal-chemical formula (Na5.42K2.0Mg0.25)[Al7.66Si28.34O72.16] • 29.86H2O has been computed hypothesizing a content of water of ca. 17%, and normalized on the basis of 36 (Si+Al). The calculated cationic site scattering from chemical formula (100.6 e−)is in good agreement with that obtained from the Rietveld refinement (105.2 e−)
Mineralogy and chemistry of the new asbestiform amphiboles from Biancavilla, Mount Etna (Sicily, Italy): differences and similarties with fluoro-edenite prismatic crystals.
No full textDetailed crystal chemical study and iron topochemistry of natural occurring asbestos (NOA): a first step to understanding their chemical reactivity.
No full textA Deep Look Into Erionite Fibres: an Electron Microscopy Investigation of their Self-Assembly
Full text linkThe exposure of humans to erionite fibres of appropriate morphology and dimension has been unambiguously linked to the occurrence of Malignant Mesothelioma. For this reason, a detailed morpho-structural investigation through Electron Microscopy techniques has been performed on erionite samples collected at two different localities, Durkee (ED) and Rome (ER), Oregon, USA. The sample from Rome has been also investigated after a prolonged leaching with Gamble's solution (ER4G) in order to evaluate the possible occurrence of morpho-structural modifications induced by this Simulated-Lung-Fluid (SLF). Here we report how the micrometric erionite fibres evolve in irregular ribbon- or rod-like bundles as a function of different nano-structural features. The reasons for the observed morphological variability have been explained by considering the structural defects located at ED surface fibrils (bi-dimensional ribbons) and the presence of nontronite, an iron-bearing clay mineral embedding the ER fibrils (mono-dimensional rods). ER4G shows a decrease in width of the rod-like fibres due to their partial digestion by SLF leaching, which synchronously dissolves nontronite. The reported results represent a valuable background toward the full comprehension of the morphological mechanisms responsible for potentially damage of lung tissue through the potential relocation of fibers to extrapulmonary sites, increasing the carcinogenic risk to humans. © 2015, Nature Publishing Group. All rights reserved
Recommended X-ray single-crystal structure refinement and Rietveld refinement procedure for tremolite
Full text linkA detailed description of the structure of the amphibole-supergroup minerals is
very challenging owing to their complex chemical composition that renders the
process of cation partition extremely difficult, particularly because of the
occurrence of multivalent elements. Since amphiboles naturally occur under a
fibrous morphology and have largely been used to produce asbestos, there is a
growing demand for detailed and accurate structural data in order to study the
relationships between structure, composition and toxicity. The present study
proposes a recommended refinement procedure for both X-ray single-crystal
structure refinement (SREF) and Rietveld analysis for tremolite, selected as a
test case. The corresponding structural results are compared to estimate the
‘degree of confidence’ of the Rietveld refinement with regard to SREF. In
particular, it is shown that the interpretation of the electron density of the
tremolite structure by SREF is model dependent. By assuming that the sitescattering
values from SREF should be as close as possible to those from
electron microprobe analysis, as a crucial constraint for the correct description
of the final crystal-chemical model, it is found that it is best satisfied by using
partially ionized scattering curves (SCs) for O and Si, and neutral SCs (neutral
oxygen curves or NOCs) for other atoms. This combination leads to the best fit
to the diffraction data. Moreover, it is found that Rietveld refinement using
NOCs produces the best structural results, in excellent agreement with SREF. It
is worth noting that, due to the complexity of the diffraction pattern and the
fairly large number of freely refinable parameters, refinements with different
combinations of SCs produce results almost indistinguishable from a statistical
point of view, albeit showing significant differences from a structural point of
view
Fibrous and asbestos-like minerals in the volcanic area of Biancavilla (Catania, Sicily, Italy): identification, classification and environmental impact assessment.
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