THE CRYSTAL STRUCTURES OF MINERAL FIBRES (2016)

Since 2011, a research project on mineral fibres entitled “Sviluppo di un modello generale di interazioni tra fibre&#13;\nminerali e cellule biologiche”, has been conducted as part of the long term Italian Research Project of National Interest&#13;\n(PRIN) “Interazione fra minerali e biosfera: conseguenze per l'ambiente e la salute umana”. The research project is&#13;\nspecifically focussed on mineral fibres and is aimed at understanding the biochemical reactions that make them cytoand&#13;\ngeno-toxic and at the development of a general model capable to classify each mineral fibre based on its toxicity&#13;\npotential.&#13;\nThe attempt to understand the complex biochemical mechanisms between the mineral fibres and the organic matter&#13;\nrequires a basic systematic mineralogical-crystallographic study. Hence, eight mineral fibres samples have been&#13;\nselected for the study based on their socio-economic and industrial importance: three chrysotile of different origin&#13;\n(UICC, Canada; Balangero and Val Malenco, Italy), four amphibole asbestos species (amosite UICC, anthophyllite&#13;\nUICC, crocidolite UICC and tremolite from Val d'Ala) and the fibrous zeolite erionite (from Jersey, Nevada, USA).&#13;\nThe surface reactivity and the chemical environment of iron within the crystal structure of these samples have been&#13;\nrecently investigated (Pollastri et al. 2014; 2015). In order to complete the crystal structural characterization, X-ray&#13;\npowder and single crystal diffraction experiments have been conducted using both conventional and synchrotron&#13;\nradiation sources (Elettra, Trieste, Italy; SLS, Villigen, Switzerland), for the determination of impurities and the&#13;\nrefinement of the crystalline structures.&#13;\nConcerning the chrysotile samples, because of the low to null effect of conventional grinding techniques on chrysotile&#13;\nfibre bundles, we have opted for a cryo-milling process in wet conditions; this procedure allowed to obtain perfectly&#13;\npowder samples. For chrysotile and erionite samples, diffraction patterns were collected with either resonant radiation at&#13;\nthe absorption K-edge of Fe (≈7 keV, λ 1.7428 Å) and with wavelength off of the absorption edge (≈10 keV, λ 1.2408&#13;\nÅ) in order to investigate the crystal chemistry of iron within the fibres.&#13;\nThe collected data were analysed both with the TOPAS and GSAS. The results of the structural refinements, in&#13;\nparticular occupancy and position of the iron atoms within the crystal structures (a primary cause of toxicity as it&#13;\ngenerate active oxygen species, mobilization by chelators and iron-catalyzed reactions; Hardy and Aust, 1995), were&#13;\ncompared to that obtained from the previously performed spectroscopic investigations.&#13;\nThe obtained structures of chrysotile samples are similar to each other and quite similar to the only available structure&#13;\nof chrysotile present in literature (Falini et al., 2004). Also the structures of other samples were compared to the few&#13;\ndata reported in literature to highlight differences between the fibrous and non fibrous forms of the minerals