Understanding the behaviour of fibrous antigorite in artificial lysosomal fluid: Evidence for toxicity assessment

Antigorite, a serpentine polymorph, can occur in an asbestos-like morphology and may pose risks to human health. For example, in New Caledonia, exposure to fibrous antigorite has been identified as one of the contributing causes to the mesothelioma epidemic that affected its population (Baumann et al., 2011). However, the toxicity of antigorite has yet to be fully defined. In the perspective of assessing the hazard of this mineral, a crucial step is to investigate its key toxicologically relevant physico-chemical properties and compare them with those of asbestos minerals. This work aimed to model biodurability, fibre surface modification, and chemical reactivity following interaction with an artificial lysosomal fluid (ALF) simulating the intracellular environment of phagocytic cells (Marques et al., 2011). Two antigorite samples from Calabria and Liguria (Italy) were investigated, along with three asbestos samples: UICC chrysotile, UICC crocidolite, and fibrous tremolite (Basilicata, Italy). Biodurability was assessed by incubating the samples in the ALF at pH 4.5 for up to 28 days at T = 37±1 °C. The leached cations were quantified by inductively coupled plasma optical emission spectrometry (ICP-OES). Surface modifications following dissolution were monitored by X-ray photoelectron spectroscopy (XPS). The focus of these analyses is on the chemical speciation of surface Fe, since Fe can catalyse, through the Fenton reaction, the generation of highly reactive hydroxyl radicals (•OH) (Andreozzi et al., 2017) capable of inducing lipid peroxidation and oxidative damage to DNA (Mossman, 2018). Chemical reactivity was evaluated by testing the release of •OH radicals in the presence of H2O2 for up to 15 days, on both pristine and incubated fibres, using the spin trapping technique coupled with electron paramagnetic resonance (EPR) spectroscopy. Results show that the biodurability of the two antigorite samples is higher than that of UICC chrysotile but significantly lower than that of UICC crocidolite and fibrous tremolite. Dissolution causes changes in Fe speciation on the surface of the fibres, and the surface alteration, in turn, leads to changes in reactivity. The observed behaviour of fibrous antigorite seems to support the hypothesis of its potential toxicity, with consequent risk to human health.