Exploiting XPS for clarifing toxicity of mineral fibers

The chemistry of surface layers of nanometer thickness can dramatically change the reac- tivity of a material. X-ray photoelectron spectroscopy (XPS) combines a high surface sensitivi- ty in the nm range with far greater spatial resolution and accuracy than ever before, allowing the understanding of the mechanisms of the chemical reactions occurring at the samples sur- face. These features together with the possibility of quantitative analysis of the outermost lay- ers of the materials make XPS technique extremely versatile for the characterization of mineral fibers, which are responsible for serious health problems and respiratory diseases. In the pre- sent work the results obtained investigating by XPS fluoro-edenite (Fantauzzi et al., 2012), crocidolite (Pacella et al., 2014), tremolite (Pacella et al., 2015) and, recently, erionite (Balli- rano et al., 2015) from different countries and after different surface treatments are summarized and discussed. Iron in fibrous minerals is reputed to be important for its biological effects, since it may catalyze the Haber – Weiss reaction, generating the reactive oxygen species ïOH. An analytical strategy was developed in order to be able to differentiate between Fe(II) and Fe(III), being the toxicity of the two cations different. In fluoro-edenite the iron chemical state was related to radical production and proposed to account for the toxicity of such fibers (Fantauzzi et al., 2012). Notably, fluoro-edenite has been declared highly dangerous for human health by the In- ternational Agency for Research on Cancer in 2014. The same XPS approach was also useful for the identification of iron chemical state following fiber incubation in solution. The surface composition of crocidolite (Pacella et al., 2014) and tremolite (Pacella et al., 2015) samples immersed in a buffered H2O2 solution (pH = 7.4) up to 168 h was monitored to shed a light on the dissolution dynamics that may occur in vivo.