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Exposure to asbestos and asbestos-like minerals has been related to the development of severe lung diseases, including cancer and malignant mesothelioma (MM). A high incidence of non-occupational MM was observed in New Caledonia (France) in people living in proximity of serpentinite outcrops, containing chrysotile and fibrous antigorite. Antigorite is a magnesium silicate, which shares with chrysotile asbestos the chemical formula. To achieve information on antigorite toxicity, we investigated the physico-minero-chemical features relevant for toxicity and cellular effects elicited on murine macrophages (MH-S) and alveolar epithelial cells (A549) of three fibrous antigorites (f-Atg) collected in a Caledonian nickel lateritic ore and subjected to supergene alteration. Field Atg were milled to obtain samples suitable for toxicological studies with a similar particle size distribution. UICC chrysotile (Ctl) and a non-fibrous antigorite (nf-Atg) were used as reference minerals. A high variability in toxicity was observed depending on shape, chemical alteration, and surface reactivity. The antigorites shared with Ctl a similar surface area (16.3, 12.1, 20.3, 13.4, and 15.6 m 2 /g for f-Atg1, 2, 3, nf-Atg, and Ctl). f-Atg showed different level of pedogenetic weathering (Ni depletion f-Atg1 ≪ f-Atg2 and 3) and contained about 50% of elongated mineral particles, some of which exhibited high aspect ratios (AR > 10 μm, 20%, 26%, 31% for f-Atg1, 2, and 3, respectively). The minerals differed in bio-accessible iron at pH 4.5 (f-Atg1 ≪ f-Atg3, < f-Atg2, nf-Atg < Ctl), and surface reactivity (ROS release in solution, f-Atg1 ≪ f-Atg2, 3, nf-Atg, and Ctl). f-Atg2 and f-Atg3 induced oxidative stress and pro-inflammatory responses, while the less altered, poorly reactive sample (f-Atg1) induced negligible effects, as well nf-Atg. The slow dissolution kinetics observed in simulated body fluids may signal a high biopersistence. Overall, our work revealed a significative cellular toxicity of f-Atg that correlates with fibrous habit and surface reactivity., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 The Authors. Published by Elsevier Inc. All rights reserved.)

Chrysotile asbestos is a carcinogenic mineral that has abundantly been used in industrial and consumer applications. The carcinogenicity of the fibers is partly governed by reactive Fe surface sites that catalyze the generation of highly toxic hydroxyl radicals (HO • ) from extracellular hydrogen peroxide (H 2 O 2 ). Chrysotile also contains Cr, typically in the low mass permille range. In this study, we examined the leaching of Cr from fibers at the physiological lung pH of 7.4 in the presence and absence of H 2 O 2 . Furthermore, we investigated the potential of cells from typical asbestos-burdened tissues and cancers to take up Cr leached from chrysotile in PCR expression, immunoblot, and cellular Cr uptake experiments. Finally, the contribution of Cr to fiber-mediated H 2 O 2 decomposition and HO • generation was studied. Chromium readily dissolved from chrysotile fibers in its genotoxic and carcinogenic hexavalent redox state upon oxidation by H 2 O 2 . Lung epithelial, mesothelial, lung carcinoma, and mesothelioma cells expressed membrane-bound Cr(VI) transporters and accumulated Cr up to 10-fold relative to the Cr(VI) concentration in the spiked medium. Conversely, anion transporter inhibitors decreased cellular Cr(VI) uptake up to 45-fold. Finally, chromium associated with chrysotile neither decomposed H 2 O 2 nor contributed to fiber-mediated HO • generation. Altogether, our results support the hypothesis that Cr may leach from inhaled chrysotile in its hexavalent state and subsequently accumulate in cells of typically asbestos-burdened tissues, which could contribute to the carcinogenicity of chrysotile fibers. However, unlike Fe, Cr did not significantly contribute to the adverse radical production of chrysotile.

In Naturally Occurring Asbestos (NOA) rich areas, water flows through asbestos bearing rocks and soils and generates waterborne fibres that may migrate in air and become a risk for humans. Research on the migration and dispersion after water vaporisation has been so far only marginally evaluated. This study investigates the migration in air of asbestos from a set of suspensions contaminated by chrysotile from Balangero (Italy), under controlled laboratory conditions. We evaluated i) the morphological modifications that might occur to chrysotile during migration from water to air, and ii) the amount of airborne chrysotile mobilised from standardised suspensions. Morphological alteration of asbestos fibres occurred during water-air migration and impacted on the analytical response of electron microscopy. Waterborne asbestos concentration higher than 40 ∙ 10 6 f/L generates in air concentration higher than 1 fibre per litre [f/L], the alarm threshold limit set by World Health Organization for airborne asbestos. A possible correlation between the waterborne fibre concentration as mass or number of fibres per volume unit [μg/L or f/L] was observed., (Copyright © 2021 The Authors. Published by Elsevier B.V. All rights reserved.)

The natural occurrence of asbestos (NOA) in rural areas is a serious concern for human health and the dispersion route of asbestos in the proximity of natural asbestos-rich settings has been marginally evaluated so far. NOA may affect air, but also water and soil quality. In rural areas population may be exposed to asbestos with a largely unknown impact on human health. This work investigates the potential exposure of a farmer cultivating a field nearby the largest former asbestos mine of Western Europe (Balangero, Italy). The concentration of waterborne asbestos in the stream used to water the field was measured (ca. 2×10(5) fibers per liter, ff/L) and the cultivated ultramafic topsoil characterized, evidencing a remarkable occurrence of chrysotile. The worker's personal exposure and the environmental fiber dispersion during a simulated agricultural activity (tillage) were quantified in two independent trials. During the trials, the worker was exposed to average concentrations of 16 and 26 ff/L, with a peak of 40 ff/L. These data inform about the possible exposure of an agricultural worker to asbestos concentration higher than the accepted threshold of 2 ff/L. The release of asbestos fibers into the environment was negligible (0-2 ff/L)., (Copyright © 2016 Elsevier B.V. All rights reserved.)

Asbestos shares with carbon nanotubes some morphological and physico-chemical features. An asbestos-like behaviour has been recently reported by some authors, though the mechanism of toxicity may be very different. To identify at the atomic level the source of toxicity in asbestos, the effect of progressive iron loading on a synthetic iron-free model nanofibre previously found non-toxic in cellular tests was studied. A set of five synthetic chrysotile nanofibres [(Mg,Fe)3(Si2O5)(OH)4] has been prepared with Fe ranging from 0 to 1.78 wt %. The relationship between fibre-induced free-radical generation and the physico-chemical characteristics of iron active sites was investigated with spin-trapping techniques on an aqueous suspension of the fibres and Mössbauer and EPR spectroscopies on the solids, respectively. The fully iron-free fibre was inert, whereas radical activity arose with even the smallest amount of iron. Surprisingly, such activity decreased upon increasing iron loading. Mössbauer and EPR revealed isolated iron ions in octahedral sites that undergo both axial and rhombic distortion and the occurrence of aggregated iron ions and/or extra-framework clustering. The isolated ions largely prevailed at the lowest loadings. Upon increasing the loading, the amount of isolated iron was reduced and the aggregation increased. A linear relationship between the formation of carbon-centred radicals and the amount of rhombic-distorted isolated iron sites was found. Even the smallest iron contamination imparts radical reactivity, hence toxicity, to any chrysotile outcrop, thereby discouraging the search for non-toxic chrysotile. The use of model solids that only differ in one property at a time appears to be the most successful approach for a molecular understanding of the physico-chemical determinants of toxicity. Such findings could also be useful in the design of safer nanofibres.

The mechanisms underlying asbestos toxicity mainly rely on experiments performed on "laboratory" fibers, but little data is available on naturally occurring asbestos (NOA). Human exposure to NOA is subject to their ecopersistence and the modulation of their potential toxicity following weathering. The effect of weathering on three fibrous minerals from the Italian Western Alps, chrysotile, tremolite, and balangeroite-a Fe-rich asbestiform mineral-was investigated by mimicking more than 100 yr of physical (freezing-thawing/wetting-drying cycles in a climatic chamber) and biochemical forces (incubation with oxalic acid). Ion release, evaluated by means of inductively coupled plasma-atomic emission spectroscopy (ICP-AES), and variation in chemical composition, evaluated by scanning electron microscopy coupled with energy-dispersive spectroscopy (SEM-EDS), indicated that weathering modified the fibers in the series: chrysotile > balangeroite > tremolite. Kinetics of ion release from the fibers (Mg, Fe, and Si) revealed different ion removal pathways. Tremolite was poorly affected. Chrysotile preferentially released cations up to a plateau, with physical and biochemical forces acting competitively. Conversely, for balangeroite, upon which weathering forces acted synergistically, the initial loss of ions facilitated further dissolution and more Si than Mg was released, suggesting an ongoing collapse of the crystal structure. Depletion of redox-reactive ions produced a significant reduction in fiber-derived *OH radicals (EPR, spin-trapping technique), but the fibrous nature was always retained. Despite weathered fibers appearing less toxic than "stored/laboratory" ones, NOA is to be considered far from safe because of fibrous nature and residual surface reactivity. Risk assessment needs to consider the effect of weathering on exposures. Both tremolite and balangeroite may contaminate, in some areas, chrysotile asbestos. However, in contrast to tremolite, balangeroite exhibits a low ecopersistence, similar to chrysotile behavior. Any contribution of balangeroite to chrysotile toxicity will thus be related to its quantitative occurrence and not to higher structural stability.

In a previous study several strains of soil fungi were reported to remove iron in vitro from crocidolite asbestos, a process that was envisaged as a possible bioremediation route for asbestos-polluted soils. Here, we get some new insight into the chemical basis of the fiber/fungi interaction by comparing the action of the most active fungal strain Fusarium oxysporum on three kind of asbestos fibers--chrysotile, amosite, and crocidolite--and on a surface-modified crocidolite. None of the fibers examined significantly inhibited biomass production. Even the smallest fibrils were visibly removed from the supernatant following adhesion to fungal hyphae. F. oxysporum, through release of chelators, extracted iron from all fibers; the higher the amount of iron at the exposed surface, the larger the amount removed, that is, crocidolite > amosite >> chrysotile. When considering the fraction of total iron extracted, however, the ranking was chrysotile > crocidolite > amosite > heated crocidolite, because of the different accessibility of the chelators to the metal ions in the crystal structure. Chrysotile was the easiest to deplete of its metal content. Iron removal fully blunted HO* radical release from crocidolite and chrysotile but only partially from amosite. The removal, in a long-term experiment, of more iron than is expected to be at the surface suggests a diffusion of ions from the bulk solid towards the surface depleted of iron by fungal activity. Thus, if the fibers could be treated with a continuous source of chelators, iron extraction would proceed up to a full inactivation of free radical release. The fungal metabolic response of F. oxysporum grown in the presence of chrysotile, amosite and crocidolite revealed that new extracellular proteins are induced--including manganese-superoxide dismutase, the typical antioxidant defense--and others are repressed, upon direct contact with the fibers. The protein profile induced by heated crocidolite was different, a result suggesting a key role for the state of the fiber/hyphae interface in protein induction.

The mechanism and kinetics of the extraction of iron ions from crocidolite asbestos have been investigated over long periods of time (30 days). Various chelators (endogenous, analytical reagents and iron sequestering drugs) have been employed. The various chelators extracted iron to different extents. Their potency was unrelated to the thermodynamic stability constant but appears linked to a sort of fitting of the molecule at the particle surface. The mechanism of extraction reveals a fast release of surface iron followed by slow ion diffusion, whereby iron flows out of the fibres. Substitution of iron by other ions present in the solution causes structural instability and collapse of the silica framework, confirmed by a parallel release of silicon into the supernatant at the end of the process. The surface shrinks and partly loses its original reactivity, however, new layers are progressively brought to the solid-liquid interface. Conversely, when the original fibres were in contact with iron bound to a weak chelator, such as Fe-NTA, the surface acts as a chelating agent and withdraws iron from the complex. This suggests that in vivo iron cycling may continuously take place at the particle surface. Modifications of the redox state of iron, following incubation in deferoxamine, are evident from cyclic voltammetry. Although deprived of iron, the deferoxamine-treated fibres exhibited a higher amount of redox cycling iron ions than the original ones. [ABSTRACT FROM AUTHOR]