Correlating dissolution kinetics, surface alterations, and chemical reactivity: new insights into the mechanisms of mineral fibre toxicity

Inhalation of respirable-sized asbestos and asbestiform mineral fibres has been associated with the development of several lung diseases, including pleural diseases [1]. Nevertheless, the understanding of the precise mechanisms driving the toxicity of mineral fibres remains incomplete. In this study, we aimed at providing further insights by i) modelling the kinetics of fibre dissolution in an artificial lysosomal fluid (ALF) that mimics the intracellular regions of phagocytic cells [2], and by ii) investigating possible fibre surface modification, following dissolution, and modulation in its chemical reactivity (as planned in the BRIC 2022 project; CUP: B87G23000090005). To comprehensively assess the possible different behaviour of mineral fibres, we studied UICC chrysotile, UICC crocidolite, fibrous tremolite (Basilicata, Italy) and two samples of fibrous antigorite (Calabria and Liguria, Italy). The samples were incubated in ALF at pH 4.5, up to 28 days at T = 37±1 °C. The leached cations were quantified by inductively coupled plasma optical emission spectrometry (ICP-OES). Chemical reactivity was evaluated following the generation of •OH radicals, an extremely reactive species, able to damage DNA, proteins, and lipids in vivo. Pristine and incubated fibres were tested up to 15 days using the spin trapping technique associated with electron paramagnetic resonance (EPR) spectroscopy. Due to the primary role of Fe in •OH radical generation [3], the chemical speciation of surface Fe was determined by X-ray photoelectron spectroscopy (XPS) on both pristine and incubated samples. The calculated dissolution rates, normalized to the specific surface area, revealed that the samples exhibit different biodurability (tremolite > crocidolite > antigorite > chrysotile). After dissolution the fibres undergo changes in surface composition, with alteration in surface Fe speciation, and reactivity. Our results suggest that different fibre dissolution rates may drive different surface chemical modifications, which in turn modulate •OH radical generation.