Simone Pollastri

The zeta potential of mineral fibres

For the first time, the zeta (ξ) potential of pathogenic mineral fibres (chrysotiles, amphiboles and erionite) was systematically investigated to shed light on the relationship between surface reactivity and fibre pathogenicity. A general model explaining the zeta potential of chrysotile, amphiboles and erionite has been postulated. In double distilled water, chrysotiles showed positive values while crocidolite and erionite showed negative values. In contact with organic solutions, all fibres exhibited negative values of zeta potential. The decrease of the surface potential is deemed to be a defensive chemical response of the macrophage cells to minimize hemolytic damage. Negatively charged surfaces favour the binding of collagen and redox activated Fe-rich proteins, to form the so-called asbestos bodies and prompt the formation of HO via the reaction with peroxide (H2O2+e(-)→HO+HO(-)). An additional mechanism accounting for higher carcinogenicity is possibly related to the Ca(2+) sequestration by the fibres with surface negative potential, impairing the mitochondrial apoptotic pathway. It was also found that with a negative zeta potential, the attractive forces prevailed over repulsions and favoured processes such as agglomeration responsible of a tumorigenic chronic inflammation.

The chemical environment of iron in mineral fibres. A combined X-ray absorption and Mössbauer spectroscopic study

Although asbestos represents today one of the most harmful contaminant on Earth, in 72% of the countries worldwide only amphiboles are banned while controlled use of chrysotile is allowed. Uncertainty on the potential toxicity of chrysotile is due to the fact that the mechanisms by which mineral fibres induces cyto- and geno-toxic damage are still unclear. We have recently started a long term project aimed at the systematic investigation of the crystal-chemistry, bio-interaction and toxicity of the mineral fibres. This work presents a systematic structural investigation of iron in asbestos and erionite (considered the most relevant mineral fibres of social and/or economic-industrial importance) using synchrotron X-ray absorption and Mössbauer spectroscopy. In all investigated mineral fibres, iron in the bulk structure is found in octahedral sites and can be made available at the surface via fibre dissolution. We postulate that the amount of hydroxyl radicals released by the fibers depends, among other factors, upon their dissolution rate; in relation to this, a ranking of ability of asbestos fibres to generate hydroxyl radicals, resulting from available surface iron, is advanced: amosite > crocidolite ≈ chrysotile > anthophyllite > tremolite. Erionite, with a fairly high toxicity potential, contains only octahedrally coordinated Fe(3+). Although it needs further experimental evidence, such available surface iron may be present as oxide nanoparticles coating and can be a direct cause of generation of hydroxyl radicals when such coating dissolves.

Crystal chemistry of the high temperature product of transformation of cement-asbestos.

In 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.

Trace elements in hazardous mineral fibres.

Both occupational and environmental exposure to asbestos-mineral fibres can be associated with lung diseases. The pathogenic effects are related to the dimension, biopersistence and chemical composition of the fibres. In addition to the major mineral elements, mineral fibres contain trace elements and their content may play a role in fibre toxicity. To shed light on the role of trace elements in asbestos carcinogenesis, knowledge on their concentration in asbestos-mineral fibres is mandatory. It is possible that trace elements play a synergetic factor in the pathogenesis of diseases caused by the inhalation of mineral fibres. In this paper, the concentration levels of trace elements from three chrysotile samples, four amphibole asbestos samples (UICC amosite, UICC anthophyllite, UICC crocidolite and tremolite) and fibrous erionite from Jersey, Nevada (USA) were determined using inductively coupled plasma mass spectrometry (ICP-MS). For all samples, the following trace elements were measured: Li, Be, Sc, V, Cr, Mn, Co, Ni, Cu, Zn, As, Rb, Sr, Y, Sb, Cs, Ba, La, Pb, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Th, U. Their distribution in the various mineral species is thoroughly discussed. The obtained results indicate that the amount of trace metals such as Mn, Cr, Co, Ni, Cu and Zn is higher in anthophyllite and chrysotile samples, whereas the amount of rare earth elements (REE) is higher in erionite and tremolite samples. The results of this work can be useful to the pathologists and biochemists who use asbestos minerals and fibrous erionite in-vitro studies as positive cyto- and geno-toxic standard references.

Assessment of asbestos body formation by high resolution FEG-SEM after exposure of Sprague-Dawley rats to chrysotile, crocidolite, or erionite.

This work presents a comparative FEG-SEM study of the morphological and chemical characteristics of both asbestos bodies and fibres found in the tissues of Sprague-Dawley rats subjected to intraperitoneal or intrapleural injection of UICC chrysotile, UICC crocidolite and erionite from Jersey, Nevada (USA), with monitoring up to 3 years after exposure. Due to unequal dosing based on number of fibres per mass for chrysotile with respect to crocidolite and erionite, excessive fibre burden and fibre aggregation during injection that especially for chrysotile would likely not represent what humans would be exposed to, caution must be taken in extrapolating our results based on instillation in experimental animals to human inhalation. Notwithstanding, the results of this study may help to better understand the mechanism of formation of asbestos bodies. For chrysotile and crocidolite, asbestos bodies are systematically formed on long asbestos fibres. The number of coated fibres is only 3.3% in chrysotile inoculated tissues. In UICC crocidolite, Mg, Si, and Fe are associated with the fibres whereas Fe, P and Ca are associated with the coating. Even for crocidolite, most of the observed fibres are uncoated as coated fibres are about 5.7%. Asbestos bodies do not form on erionite fibres. The crystal habit, crystallinity and chemistry of all fibre species do not change with contact time, with the exception of chrysotile which shows signs of leaching of Mg. A model for the formation of asbestos bodies from mineral fibres is postulated. Because the three fibre species show limited signs of dissolution in the tissue, they cannot act as source of elements (primarily Fe, P and Ca) promoting nucleation and growth of asbestos bodies. Hence, the limited number of coated fibres should be due to the lack of nutrients or organic nature.

Determination of the concentration of asbestos minerals in highly contaminated mine tailings: An example from abandoned mine waste of Crètaz and Èmarese (Valle d’Aosta, Italy)

Abstract For the first time, this work reports concentration maps of asbestos minerals in contaminated mine tailings drawn using the results of Rietveld quantitative phase analysis (QPA). The investigated sites are located in the Valle d’Aosta region (Italy): Crètaz, the most important Italian magnetite mine, active until 1979 and Emarèse, one the most important chrysotile asbestos mines in Italy, active until 1968. The results of the study permit to draw the spatial distribution of the asbestos (chrysotile and tremolite in this specific case) concentration, useful to plan reclamation of the sites, with priority given to the areas with the highest asbestos concentration. Because of the complexity of the mineral assemblage, which includes, among the others, antigorite, chlorite, talc, and tremolite, the concentration of chrysotile was cross-checked using different experimental techniques such as X-ray powder diffraction (XRPD), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), polarized light optical microscopy (PCOM), and differential thermal analysis (DTA). The accuracy of the results was validated by analyzing standard samples with known concentrations of chrysotile and tremolite. The comparison allowed to point out the advantages and disadvantages of each experimental method. At Crètaz, chrysotile ranges from 4.4 to 22.8 wt% and tremolite from 1.0 to 10.3 wt%, whereas at Emarèse the concentration of chrysotile varies from 3.3 to 39.5 wt% and tremolite from 5.9 to 12.4 wt%. Antigorite and chlorite are the major accompanying phases with variable amounts of other accessory minerals including magnetite, carbonates, talc, olivine, pyroxene, talc, and brucite. The results of our study are of key importance for the local environmental policies as the knowledge of the spatial distribution of the asbestos concentration allows to plan a detailed reclamation agenda of the contaminated sites. The spots with the highest surface contamination of both chrysotile and tremolite were identified and classified as priority areas in the reclamation plan.

Where is iron in erionite? A multidisciplinary study on fibrous erionite-Na from Jersey (Nevada, USA)

Fibrous erionite is a mineral fibre of great concern but to date mechanisms by which it induces cyto- and geno-toxic damage, and especially the role of iron associated to this zeolite species, remain poorly understood. One of the reasons is that we still don’t know exactly where iron is in natural erionite. This work is focused on fibrous erionite-Na from Jersey (Nevada, USA) and attempts to draw a general model of occurrence of iron in erionite and relationship with toxicity mechanisms. It was found that iron is present as 6-fold coordinated Fe3+ not part of the zeolite structure. The heterogeneous nature of the sample was revealed as receptacle of different iron-bearing impurities (amorphous iron-rich nanoparticles, micro-particles of iron oxides/hydroxides, and flakes of nontronite). If iron is not part of the structure, its role should be considered irrelevant for erionite toxicity, and other factors like biopersistence should be invoked. An alternative perspective to the proposed model is that iron rich nano-particles and nontronite dissolve in the intracellular acidic environment, leaving a residue of iron atoms at specific surface sites anchored to the windows of the zeolite channels. These sites may be active later as low nuclearity groups.

The concept of ‘end of waste’ and recycling of hazardous materials: in depth characterization of the product of thermal transformation of cement-asbestos

Abstract Selected samples of asbestos-containing material (ACM) with different Ca/Si ratios have been treated thermally at 1200ºC for 15 min to obtain an ‘end of waste geo-inspired material’. Before and after treatment, micro-Raman spectroscopy allowed the investigation of both powdered and massive samples by directing the laser beam onto crystals with elongated morphology, thin fibres and the matrix. In the raw samples, chrysotile and/or crocidolite were detected. After the thermal treatment, no asbestos phases were identified in the Raman spectra collected on fibrous or fibre-like morphologies. The scanning electron microscopy/energy dispersive spectroscopy investigations confirmed the onset of a pseudomorphic process during annealing, leading to the complete transformation of asbestos minerals into non-hazardous magnesium or calcium magnesium silicates such as forsterite, monticellite, åkermanite and merwinite. The identification of such mineral assemblages was inspired by the close inspection of a natural counterpart, the high-temperature contact metamorphic imprint due to the intrusion of a sill into carbonate rocks. The process turned out to occur largely at the solid state and involved substantial mobilization of Ca and Mg to form a spinel phase (namely MgFe2O4) which was recognized in the matrix and within, or close to elongated morphologies.

New insights into the toxicity of mineral fibres: A combined in situ synchrotron μ-XRD and HR-TEM study of chrysotile, crocidolite, and erionite fibres found in the tissues of Sprague-Dawley rats

Along the line of the recent research topic aimed at understanding the in vivo activity of mineral fibres and their mechanisms of toxicity, this work describes the morpho-chemical characteristics of the mineral fibres found in the tissues of Sprague-Dawley rats subjected to intraperitoneal/intrapleural injection of UICC chrysotile, UICC crocidolite and erionite-Na from Nevada (USA). The fibres are studied with in situ synchrotron powder diffraction and high resolution transmission electron microscopy to improve our understanding of the mechanisms of toxicity of these mineral fibres. In contact with the tissues of the rats, chrysotile fibres are prone to dissolve, with leaching of Mg and production of a silica rich relict. On the other hand, crocidolite and erionite-Na fibres are stable even for very long contact times within the tissues of the rats, showing just a thin dissolution amorphous halo. These findings support the model of a lower biopersistence of chrysotile with respect to crocidolite and erionite-Na but the formation of a silica-rich fibrous residue after the pseudo-amorphization of chrysotile may justify a higher cytotoxic potential and intense inflammatory activity of chrysotile in the short term in contact with the lung tissues.

The crystal structure of mineral fibres: 1. Chrysotile

This work reports the result s of the structural study of three representative chrysotile samples of different provenance (Canadian UICC, and Italian Balangero and Valmalenco) . Chemical composition was determined using EMPA and TG data. An innovative wet cryo-milling procedure was used to powder the resistant-to-abrasion chrysotile fibres. X-ray powder diffraction patterns were collected using both conventional and non-conventional sources. Collected data were used for Rietveld structural refinements and results were compared with available literature data. The three samples display similar structure models, although small differences were detected in the position of the oxygen atoms. Both the structural refinements and spectroscopic investigations confirms that Fe 2+ and Fe 3+ atoms in chrysotile are located in the octahedral cavities only, substituting for Mg 2+ . Regarding the atom coordinates, UICC chrysotile is the more similar to the model reported by Falini et al. (2004). About the lattice parameters, the Valmalenco chrysotile is the more similar, if compared with the Balangero and UICC, to both the model proposed by Whittaker (1956a,b) and Falini et al. (2004) . This work is intended as a basis for subsequent studies aimed at understanding the potential toxicity of these mineral fibres.