84 research outputs found
Caratterizzazione cristallochimica e chimico-fisica delle fibre minerali finalizzata alla comprensione del loro potenziale tossicologico
No full textCon il termine "fibre minerali" si intende un gruppo di minerali naturali diffuso in tutta la Terra. Tra questi, i più rilevanti e certamente i più temuti sono i minerali dell’amianto e le zeoliti fibrose come l'erionite. Questi minerali rappresentano un interessante oggetto di studio in quanto i meccanismi con cui inducono danni a livello cito- e geno-tossico rimangono poco chiari e manca la comprensione del rapporto causa-effetto tra l'esposizione alle fibre e l'insorgenza delle malattie. Le difficoltà derivano dalla grande variabilità chimica, morfologica e strutturale di questi minerali, che influenza fortemente le reazioni biogeochimiche.
Per questi motivi, la presente tesi di dottorato si propone di contribuire alla valutazione dei meccanismi di interazione e di tossicità biologica del crisotilo, degli anfiboli e dell'erionite, partendo da una solida caratterizzazione sistematica delle loro proprietà.
Per lo studio, sono state selezionate 8 fibre di importanza sociale ed economico-industriale. Le impurità sono state individuate e quantitativamente stimate servendosi della diffrazione di raggi X da polveri (XRPD) cui è seguito lo studio della reattività di superficie, attraverso misure di potenziale Zeta e di area superficiale.
Successivamente l'attenzione si è focalizzata sull'ambiente chimico del ferro all'interno delle strutture cristalline, mediante spettroscopia di assorbimento di raggi X (XAS) e spettroscopia Mössbauer.
Una volta ottenuto un quadro soddisfacente dal punto di vista fisico-chimico e mineralogico, le indagini sono state indirizzate ai cambiamenti strutturali subiti dalle fibre dopo essere state in contatto con colture cellulari umane, tramite μXANES, μXRD e mappatura XRF del ferro in situ con luce di sincrotrone.
Sono stati inoltre condotti esperimenti di dissoluzione su fibre di crisotilo in contatto con una soluzione che simula i fluidi polmonari (S.L.F.) mentre gli esperimenti su anfiboli ed erionite sono tuttora in corso.
I principali risultati possono essere così sintetizzati:
1) Tutte le fibre a contatto con la soluzione S.L.F. mostrano valori di potenziale Zeta negativi e simili tra loro, cadendo nell'intervallo di valori in cui è favorita l'aggregazione delle fibre. Tale comportamento potrebbe virtualmente pregiudicare la risposta apoptotica attraverso il sequestro di ioni Ca2+.
2) In tutti i campioni il ferro è stato trovato in coordinazione ottaedrica, con gli ioni Fe2+ situati nelle posizioni della struttura meno influenzate dall'ossidazione. Considerando il tempo di dissoluzione più breve del crisotilo rispetto agli anfiboli (sebbene questi ultimi siano più ricchi in ferro) il rilascio di ferro potrebbe essere comparabile. rappresenta un caso particolare poiché il ferro è presente solo come Fe3+ in coordinazione ottaedrica all'interno di un rivestimento superficiale di nanoparticelle di ossido.
3) Il contatto delle fibre di crisotilo con le colture cellulari porta alla loro amorfizzazione, poi seguita dalla dissoluzione in senso stretto. La crocidolite mostra lievi segni precoci di amorfizzazione mentre l'erionite sembra essere la specie fibrosa più stabile a contatto con le cellule. La formazione di uno scheletro siliceo fibroso in seguito alla pseudo-amorfizzazione del crisotilo potrebbe indurre la produzione di radicali ossidrili in sinergia con le specie di ferro presenti in superficie; quindi il crisotilo potrebbe essere molto più reattivo e citotossico in vitro nel breve termine, mentre l'attività della crocidolite e dell'erionite sarebbe più lenta ma persistente nel lungo termine. Il lavoro qui descritto rappresenta un ulteriore passo verso lo sviluppo di un modello generale che descriva il complesso meccanismo di interazione tra fibre e ambiente cellulare.With the general term “mineral fibres” is intended a group of natural minerals widespread throughout the Earth. Among them, the most relevant and certainly the most feared ones are asbestos minerals and fibrous zeolites such as erionite. These minerals represent an interesting subject of study since the mechanisms by which they induces cyto- and geno-toxic damage remain unclear and there is a lack in understanding the cause-effect relationship between exposure to the fibres and the onset of the disease. The difficulties arise from the great chemical, morphological and structural variability of these minerals, which affect the biogeochemical reactions.
For these reasons, the present doctoral thesis aims to contribute to the assessment of the interaction mechanisms and biological toxicity of chrysotile, amphyboles and erionite, starting from a strong systematic characterization of their properties.
For the study, 8 mineral fibres of social and economic-industrial importance were selected. The impurities were detected and quantitatively estimated by using XRPD both from conventional and unconventional sources; the following step was the characterization of the surface reactivity, through Zeta potential and surface area measurements. Subsequently the focus has shifted on the chemical environment of iron within the crystal structures, using X-ray absorption and Mössbauer spectroscopy.
Once obtained a satisfactory general picture from the physical-chemical and mineralogical point of view, investigations were addressed on aspects of biological interaction. Specifically, we have studied the structural changes undergone by the fibres after being in contact (for different times) with human cell cultures, using in situ synchrotron XRF iron mapping, μXANES, and μXRD. Moreover, in recent months, dissolution experiments on chrysotile fibres have been conducted in contact with simulated lung fluid solution (S.L.F.) at acidic pH; dissolution experiments on amphiboles and erionite are still in progress.
The main results can be summarized as follows:
1) All amphibole, chrysotile and erionite fibres, when in contact with S.L.F. solution, display negative Zeta potentials and minor differences, falling in the range of values where the agglomeration of fibres is favoured. Such behaviour may virtually impair apoptotic response via the sequestration of Ca2+ ions.
2) In all investigated fibres, iron has been found in octahedral cavities, with Fe2+ ions located in the innermost structure positions inside the crystal lattice less affected by oxidation. Taking into account the much shorter dissolution time of chrysotile with respect to amphiboles (although the latter are much more rich in iron) the release of iron could be comparable. Erionite turns out to be a special case since iron is present as octahedrally coordinated Fe3+ likely inside a surface coating of oxide nanoparticles.
3) The contact of the chrysotile fibres with the cell cultures leads to amorphization, interpreted as the first dissolution step, later followed by dissolution sensu stricto. Crocidolite shows minor early signs of amorphization whereas erionite seems to be the more stable fibre species in contact with the cells. The formation of a silica-rich fibre skeleton after pseudo-amorphization of chrysotile may prompt the production of hydroxyl radicals in synergy with surface iron species; this could indicate that chrysotile may be much more reactive and cytotoxic in vitro in the short term whereas the activity of crocidolite and erionite would be much more sluggish but persistent in the long term.
The work presented here could be helpful for the development of a general model describing the complex mechanism of interaction between fibres and cellular environment
Bulk spectroscopy of mineral fibres
No full textSpectroscopic methods are utilized widely for characterizing minerals and other geomaterials
in terms of electronic, vibrational and nuclear properties. The basics and
applications of spectroscopic methods in mineralogy were reported comprehensively by
Hawthorne (1988), and later discussed carefully and updated by Burns (1993) and Clark
(1999), by Beran and Libowitzky (2004) and more recently by Henderson et al. (2014).
These esteemed books and reviews focused generally on topics of immediate
mineralogical interest, but nevertheless contain stimulating parallel excursions into the
fields of geology and materials sciences. This chapter is built on the shoulders of those
giants and is devoted specifically to exploring spectroscopic investigations of electronic
and nuclear properties of mineral fibres, a topic not reviewed previously. A number of
spectroscopies (though not all) will be mentioned without covering in detail their
physical bases (which can be found easily in the books and reviews mentioned above),
because this chapter is intended to serve as a review of their contribution to increasing
comprehension of the bulk properties of mineral fibres
Inorganic polymers from laterite using activation with phosphoric acid and alkaline sodium silicate solution: Mechanical and microstructural properties
No full textGeopolymers from laterite, an iron-rich soil available in developing countries, have great potential as building materials. In this work, laterite from Togo (Africa) was used to prepare geopolymers using both phosphoric acid and alkaline sodium silicate solution. Microstructural properties were investigated by scanning electron microscopy, X-ray powder diffraction and mercury porosimetry, whereas thermal properties were evaluated by thermal analyses. The local environment of iron was studied by X-ray Absorption Spectroscopy (XANES region). The mechanical properties were determined. Modulus of Rupture and Young's modulus fell in the ranges 3.3–4.5 MPa and 12–33 GPa, respectively, rendering the materials good candidates for construction purposes. Heating above 900 °C results in weight-gain, presumably due to iron redox reactions. X-ray Absorption Spectroscopy data evidence changes in the chemical and structural environments of iron following thermal treatment of geopolymers. These changes indicate interaction between the geopolymer structure and iron during heating, possibly leading to redox properties
Solubilization and coordination of the HgCl2 molecule in water, methanol, acetone, and acetonitrile: an X-ray absorption investigation
No full textX-ray absorption spectroscopy (XAS) has been employed to carry out structural characterization of the local environment around mercury after the dissolution of the HgCl2 molecule. A combined EXAFS (extended X-ray absorption fine structure) and XANES (X-ray absorption near edge structure) data analysis has been performed on the Hg L3-edge absorption spectra recorded on 0.1 M HgCl2 solutions in water, methanol (MeOH), acetone and acetonitrile. The Hg-Cl distance determined by EXAFS (2.29(2)-2.31(2) Å) is always comparable to that found in the HgCl2 crystal (2.31(2) Å), demonstrating that the HgCl2 molecule dissolves in these solvents without dissociating. A small sensitivity of EXAFS to the solvent molecules interacting with HgCl2 has been detected and indicates a high degree of configurational disorder associated with this contribution. XANES data analysis, which is less affected by the disorder, was therefore carried out for the first time on these systems to shed light into the still elusive structural arrangement of the solvent molecules around HgCl2. The obtained results show that, in aqueous and MeOH solutions, the XANES data are compatible with three solvent molecules arranged around the HgCl2 unit to form a trigonal bipyramidal structure. The determination of the three-body Cl-Hg-Cl distribution shows a certain degree of uncertainty around the average 180° bond angle value, suggesting that the HgCl2 molecule probably vibrates in the solution around a linear configuration
Environmental impacts and risk assessment in the re-use of Cr-bearing pyrolyzed tannery wastes: A case study in a residential area
No full textIncreasing concern has been raised on the environmental impacts of chromium-tanning wastes recycling. In particular, the pyrolytic conversion of leather industry sludges into Cr(VI)-free carbonized residues is believed to represent a viable route for a sustainable re-use of this type of wastes. The aim of this study was to determine the impact of recycled Cr-bearing pyrolyzed char (named KEU) as backfilling material for road construction in an urban area in Tuscany (Italy). Geochemical and chromium-isotope data, together with microstructural analyses (HR-TEM and XAS), indicate that the presence of KEU results in a significant enhancement of the natural Cr background. The results support the hypothesis that, in environmental conditions, the Cr (III) hosted in KEU is converted into Cr(VI), which is leached out by rainwater. Indeed, Cr(VI) is dispersed in surface water, reaching concentrations up to 18 mg/L and it also occurs in coatings on the surface gravel of unpaved roads. The 53Cr/52Cr ratio measured in KEU, reported in δ53Cr notation, was in the restricted range δ53Cr = −0.031 ± 0.057 ‰; on the contrary, the δ53Cr in water varied between +1.581 ± 0.038 ‰ and +3.261 ± 0.191 ‰, indicating the reduction of Cr(VI) after the pristine oxidative mobilization. The risk-based soil screening levels (SSLs) for total Cr are well above the concentration measured in soil for all the exposure pathways. On the contrary, the SSL for Cr(VI)indicates that soil contamination poses health hazards for residents
In vitro acellular dissolution of mineral fibres: A comparative study
No full textThe study of the mechanisms by which mineral fibres promote adverse effects in both animals and humans is a hot topic of multidisciplinary research with many aspects that still need to be elucidated. Besides length and diameter, a key parameter that determines the toxicity/pathogenicity of a fibre is biopersistence, one component of which is biodurability. In this paper, biodurability of mineral fibres of social and economic importance (chrysotile, amphibole asbestos and fibrous erionite) has been determined for the first time in a systematic comparative way from in vitro acellular dissolution experiments. Dissolution was possible using the Gamble solution as simulated lung fluid (pH = 4 and at body temperature) so to reproduce the macrophage phagolysosome environment. The investigated mineral fibres display very different dissolution rates. For a 0.25 μm thick fibre, the calculated dissolution time of chrysotile is in the range 94-177 days, very short if compared to that of amphibole fibres (49-245 years), and fibrous erionite (181 years). Diffraction and SEM data on the dissolution products evidence that chrysotile rapidly undergoes amorphization with the formation of a nanophasic silica-rich fibrous metastable pseudomorph as first dissolution step whereas amphibole asbestos and fibrous erionite show minor signs of dissolution even after 9-12 months
Infra Red spectroscopy of the regulated asbestos amphiboles
No full textVibrational spectroscopies (Fourier Transform Infra Red, FTIR, and Raman) are exceptionally valuable tools for the identification and crystal–chemical study of fibrous minerals, and asbestos amphiboles in particular. Raman spectroscopy has been widely applied in toxicological studies and thus a large corpus of reference data on regulated species is found in the literature. However, FTIR spectroscopy has been mostly used in crystal–chemical studies and very few data are found on asbestos amphiboles. This paper is intended to fill this gap. We report new FTIR data collected on a suite of well-characterized samples of the five regulated amphibole species: anthophyllite, amosite, and crocidolite, provided by the Union for International Cancer Control (UICC) Organization, and tremolite and actinolite, from two well-known occurrences. The data from these reference samples have been augmented by results from additional specimens to clarify some aspects of their spectroscopic features. We show that the FTIR spectra in both the OH-stretching region and in the lattice modes region can be effective for rapid identification of the asbestos type
Capabilities of a novel electrochemical cell for operando XAS and SAXS investigations for PEM fuel cells and water electrolysers
No full textCatalyst stability is a key issue in current electrochemical devices, such as fuel cells (FCs) and water electrolysers (WEs). While for FCs, the main degradation process limiting catalyst stability have been highlighted, a clear picture is still missing concerning WEs. In this framework, in operando analyses are essential to characterize catalyst degradation over time. As X-Rays constitute the perfect probe for studying catalytic materials, we here present a reversible electrochemical cell designed for operando X-Ray Absorption Spectroscopy and Small and Wide Angle X-Ray Scattering analyses, which was used: (i) to study Pt/C catalyst degradation coupling the evolution of specific electrochemically active surface area (ECSA) with catalyst morphology, supported by the analysis of Pt oxidation state. As a result, an increase of particle (and particle cluster) size is connected to the diminishing of ECSA and to the changes in the fraction of metallic-to-oxidised Pt, underlying that changes mainly develop in the first 2000 cycles of applied stress tests. Finally, (ii) we introduce some preliminary results underlying the change in Ir oxidation state for a standard Ir/IrOX catalyst material for WEs, showing as such a change is not sufficient to induce any remarkable morphological variations within 500 cycles of stress tests
Insight on GA-ferrierite catalyst: X ray powder diffraction characterization at ambient conditions
No full textCrystal chemistry of the high temperature product of transformation of cement-asbestos
No full textIn this work, the high-temperature inertization product of a representative batch of samples of cement-asbestos (CA) from different localities in Italy have been characterized with a multidisciplinary approach. All the raw CA samples were heated at 1200°C for 15 min. After firing, they underwent a series of solid state reactions leading to global structural changes of the matrix. Effects of annealing time and temperature on the crystallization kinetics were thoroughly investigated. Both factors acted in favour of equilibrium. Three classes of CA were identified with the aid of phase diagrams and of specific plots relating chemical and mineralogical parameters. This result was considered of importance in view of the potential use of transformed cement-asbestos as a secondary raw material. In principle, the content of CA packages removed from the environment and their corresponding heat-treated products can be classified simply using XRF. This method allows for the selection of appropriate fractions in function of the most suitable recycling solution adopted. Samples belonging to the class called larnite-rich, turned out to be of great interest as possible candidate for substituting a fraction of cement in many building materials and innovative green cement productions
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