Synchrotron X-ray imaging for characterizing chrysotile asbestos

Over the last decades, rocks containing Naturally Occurring Asbestos (NOA) have been widely studied by many authors with the aim of determining the potential health risks to exposed neighboring populations. It is difficult to accurately characterize the asbestos fibres contained within the rocks as conventional techniques are not effective and have drawbacks associated with the disturbance of the sample under study. Indeed, the size and geometric shape ratios of asbestos chrysotile fibres can be subjected to change, thus leading to the misevaluation of asbestiform fibre findings. In this frame, our study aims to determine the characteristics of the veins that form in serpentinite (i.e. shape) and their infill (i.e. size of fibres), without grinding and/or particle size reduction.

To obtain this ambitious goal, X-ray synchrotron microtomography (SR-μCT) supplemented with polarized light microscope (PLM), scanning electron microscopy analysis combined with energy dispersive spectrometry (SEM/EDS), electron probe micro-analysis (EPMA) were used for identifying asbestos fibres in a mineral matrix. In the specific case, we analyzed a representative set of veins and fibrous chrysotile that fills the veins, taken from massive serpentinite outcrops (Southern-Italy; Bloise and Miriello, 2008). The non-destructive SR-μCT technique allowed to identify respirable chrysotile fibres (regulated asbestos) within the serpentinite matrix and to reconstruct the 3D structures of infill chrysotile asbestos fibres as well as other phase, whose structures were not resolvable with PLM, SEM or EPMA. Moreover, due to differences in chemical composition between veins and matrix, the obtained data enabled to evaluate the vein shapes present in the massive serpentinite matrix. In particular, iron and aluminum distribution variations between veins and matrix induce different radiation absorption patterns, thus permitting a detailed image-based 3D geometric reconstruction (Bloise et al., 2019). The results proved that SR-μCT is a valuable and promising technique for analyzing asbestos chrysotile that fills the veins within massive serpentinite. The 3D images of veins may help to identify NOA contained within serpentinite rocks.

References:

Bloise, A., Miriello, D., 2018. Multi-analytical approach for identifying asbestos minerals in situ. Geosci. 8 (4), 133. https://doi.org/10.3390/geosciences8040133.

Bloise, A., Ricchiuti, C., Lanzafame, G., Punturo, R., 2019. X-ray synchrotron microtomography: a new technique for characterizing chrysotile asbestos, Sci. Total Environ. https://doi.org/10.1016/j.scitotenv.2019.135675