Identification of iron compounds in chrysotile from the Balangero mine (Turin, Italy) by micro-Raman spectroscopy

Chrysotile, one of the six regulated asbestos minerals, is classified as carcinogenic to humans by the International Agency for Research on Cancer. The Balangero mine (Turin, Italy) was the largest asbestos mine in Europe, providing extraction of chrysotile fibers until 1990. Chrysotile from Balangero is currently of great interest in fibers toxicity studies focused on the understanding of the mechanisms that induce lung malignancies. One of the crucial factors in the biochemical reactions is the presence of Fe at the fibers surface. Surface reactivity is responsible for the generation of reactive oxygen species, which play an important role in asbestos cyto-genotoxicity. Moreover, the dissolution of Fe-bearing phases in the acidic environment of the lysosomes might be considered as possible release of hazardous Fe ions in the lungs. Here, chrysotile from Balangero was characterized by micro-Raman spectroscopy and scanning electron microscope-energy dispersive system (SEM-EDS) analysis to identify the Fe-bearing impurities associated with asbestos fibers. Micrometric crystals were recognized as Fe oxides, carbonates, and sulfides. Uncommonly reported phases in asbestos minerals were also identified, mainly as mackinawite (Fe(II)S), in different forms. The nature of the Fe compounds containing both Fe(II) and Fe(III) species was verified by micro-Raman spectroscopy combined with SEM-EDS analysis.