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Background: Exposure to some - but not all - quartz particles is associated to silicosis, lung cancer and autoimmune diseases. What imparts pathogenicity to any single quartz source is however still unclear. Crystallinity and various surface features are implied in toxicity. Quartz dusts used so far in particle toxicology have been obtained by grinding rocks containing natural quartz, a process which affects crystallinity and yields dusts with variable surface states. To clarify the role of crystallinity in quartz pathogenicity we have grown intact quartz crystals in respirable size. Methods: Quartz crystals were grown and compared with a fractured specimen obtained by grinding the largest synthetic crystals and a mineral quartz (positive control). The key physico-chemical features relevant to particle toxicity - particle size distribution, micromorphology, crystallinity, surface charge, cell-free oxidative potential - were evaluated. Membranolysis was assessed on biological and artificial membranes. Endpoints of cellular stress were evaluated on RAW 264.7 murine macrophages by High Content Analysis after ascertaining cellular uptake by bio-TEM imaging of quartz-exposed cells. Results: Quartz crystals were grown in the submicron (n-Qz-syn) or micron (μ-Qz-syn) range by modulating the synthetic procedure. Independently from size as-grown quartz crystals with regular intact faces did not elicit cellular toxicity and lysosomal stress on RAW 264.7 macrophages, and were non-membranolytic on liposome and red blood cells. When fractured, synthetic quartz (μ-Qz-syn-f) attained particle morphology and size close to the mineral quartz dust (Qz-f, positive control) and similarly induced cellular toxicity and membranolysis. Fracturing imparted a higher heterogeneity of silanol acidic sites and radical species at the quartz surface. Conclusions: Our data support the hypothesis that the biological activity of quartz dust is not due to crystallinity but to crystal fragmentation, when conchoidal fractures are formed. Besides radical generation, fracturing upsets the expected long-range order of non-radical surface moieties - silanols, silanolates, siloxanes - which disrupt membranes and induce cellular toxicity, both outcomes associated to the inflammatory response to quartz. [ABSTRACT FROM AUTHOR]

Sugarcane combustion generates fine-grained particulate that has the potential to be a respiratory health hazard because of its grain size and composition. In particular, conversion of amorphous silica to crystalline forms during burning may provide a source of toxic particles. In this study, we investigate and evaluate the toxicity of sugarcane ash and bagasse ash formed from commercial sugarcane burning. Experiments to determine the main physicochemical properties of the particles, known to modulate biological responses, were combined with cellular toxicity assays to gain insight into the potential reactions that could occur at the particle-lung interface following inhalation. The specific surface area of the particles ranged from ∼16 to 90 m2 g−1. The samples did not generate hydroxyl- or carbon-centered radicals in cell-free tests. However, all samples were able to 'scavenge' an external source of hydroxyl radicals, which may be indicative of defects on the particle surfaces that may interfere with cellular processes. The bioavailable iron on the particle surfaces was low (2-3 μmol m−2), indicating a low propensity for iron-catalyzed radical generation. The sample surfaces were all hydrophilic and slightly acidic, which may be due to the presence of oxygenated (functional) groups. The ability to cause oxidative stress and membrane rupture in red blood cells (hemolysis) was found to be low, indicating that the samples are not toxic by the mechanisms tested. Cytotoxicity of sugarcane ash was observed, by measuring lactate dehydrogenase release, after incubation of relatively high concentrations of ash with murine alveolar macrophage cells. All samples induced nitrogen oxide release (although only at very high concentrations) and reactive oxygen species generation (although the bagasse samples were less potent than the sugarcane ash). However, the samples induced significantly lower cytotoxic effects and nitrogen oxide generation when compared with the positive control. © 2012 Wiley Periodicals, Inc. Environ Toxicol 29: 503-516, 2014. [ABSTRACT FROM AUTHOR]

To evaluate the effect of carbonaceous materials on thepathogenicactivity of quartz dusts, mixtures of carbon soot (1 and 10%) andquartz (Min-U-Sil) were prepared and then milled so to attain an intimateassociation of carbon and the quartz surface. Both cellular and cell-freetests show that carbon associated to quartz completely inhibits thetypical free radical generation of quartz dusts (through Fenton activityand homolytic cleavage of a C–H bond) and suppresses the oxidativestress and inflammation induced by quartz alone on MH-S murine macrophagecells (lipid peroxidation, nitric oxide release, and tumor necrosisfactor-α synthesis). The cytotoxic response to quartz is alsolargely reduced. An extremely pure quartz milled with 10% of sootshowed inactivating effects on the adverse reactions to quartz similarto Min-U-Sil quartz. None of these effects takes place when the sameexperiments are carried out with mechanically mixed samples, whichsuggests that carbon acts not just as a radical quencher but becauseof its association to the quartz surface. [ABSTRACT FROM AUTHOR]

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The continuous ash and gas emissions from the Tavurvur cone in Rabaul caldera, Papua New Guinea, during 2007-08, raised concerns regarding how exposure would affect the respiratory health of nearby populations and impact on the environment. As part of a formal evaluation of the effects of volcanic emissions on public health, we investigated the potential health hazard of the ash using a suite of selected mineralogical analyses and in vitro toxicity screening tests. The trachy -andesitic ash comprised 2.1-6.7 vol.% respirable (sub -4 μm diameter) particles. The crystalline silica content was 1.9-5.0 wt.% cristobalite (in the bulk sample) with trace amounts of quartz and/or tridymite. Scanning electron microscopy showed that the ash particles were angular with sparse, fibre -like particles (∼3-60 μm max. diameter) observed in some samples, which we confirmed to be CaSO (gypsum, at <6 wt.% in the bulk samples) and not asbestiform fibres. The ash specific surface area was low (0.1-2.7 m g). The leached solution from one of the ash samples was slightly acidic (pH 5.6), but did not contain high levels of toxic metals (such as F, Cu, Zn, Mn, As, Ni and Cd) when compared to previously tested volcanic ash leachates. Ash samples generated potentially -harmful hydroxyl radicals through an iron -mediated catalytic reaction, in the range of 0.15-2.47 μmol m (after 30 min of reaction). However, measurement of particle oxidative capacity (potential oxidative stress reaction using ascorbic acid) and silica -like injury to red blood cells (erythrolysis assay, i.e. measurement of cell death) nevertheless revealed low biological reactivity. The findings suggest that acute exposure to the ash would have a limited potential to exacerbate pre -existing conditions such as asthma or chronic bronchitis, and the potential for chronic exposure leading to silicosis was low. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Refractory ceramic fibres (RCFs) are amorphous fibres made up of various metal oxides (mainly Al2O3 and SiO2), used as high temperature insulation materials. We have examined the surface properties of three RCFs from the TIMA repository, RCF1, RCF3 and RCF4 (RCF1 heated at the expected working temperature), which showed different potentials for cytotoxicity and the induction of morphological transformation in Syrian hamster embryo cells, RCF4 being less active. The degree of surface hydrophilicity, evaluated by adsorption calorimetry, showed that RCF4 is less hydrophilic than RCF1, likely as a consequence of the prior thermal treatment. In order to investigate the effect of thermal treatment on the cellular response to RCFs we have heated (800°C for 24h) the most active fibre (RCF3) in air until it was converted to a fully hydrophobic material. The cytotoxic (colony forming efficiency) and transforming potencies of heated and unheated RCF3, measured at concentrations between 1 and 16 Îg/cm² of culture dish for 7 days, were then compared. Both cytotoxicity and potential to transform cells dramatically decreased when fibres were heated, indicating that hydrophobicity blunts the cellular response to RCF3. These results confirm that the state of the surface of RCFs modulates the biological response elicited and that a correlation exists between the degree of surface hydrophilicity and induction of cell damage and transformation. Thermal treatment, by lowering the surface affinity of RCFs for water, inhibits some cell-fibre interactions and decreases the extent of internalization of the fibres. [ABSTRACT FROM AUTHOR]

Oxygen radical generation due to surface radicals, inflammation, and iron release has been suggested as the mechanism of adverse effects of quartz, such as emphysema, fibrosis, and carcinogenic effects. Therefore, we measured iron release, acellular generation of hydroxyl radicals, and oxidative DNA damage and cytotoxicity in rat lung epithelial (RLE) cells by different coal fly ashes (CFA) that contain both quartz and iron. Seven samples of CFA with different particle size and quartz content (up to 14.1%) were tested along with silica (alpha-quartz), ground coal, and coal mine dust (respirable) as positive control particles, and fine TiO2 (anatase) as a negative control. Five test samples were pulverized fuel ashes (PFA), two samples were coal gasification (SCG) ashes (quartz content <0.1% ), and one sample was a ground coal. No marked differences between SCG and PFA fly ashes were observed, and toxicity did not correlate with physicochemical characteristics or effect parameters. Stable surface radicals were only detected in the reference particles silica and coal mine dust, but not in CFA. On the other hand, hydroxyl radical generation by all fly ashes was observed in the presence of hydrogen peroxide, which was positively correlated with iron mobilization and inhibited by deferoxamine, but not correlated with iron or quartz content. Also a relationship between acellular hydroxyl radical generation and oxidative DNA damage in RLE cells by CFA was observed. Differences in hydroxyl radical generation and oxidative damage by the CFA were not related to iron and quartz content, but the respirable ashes (MAT023, 38, and 41) showed a very extensive level of hydroxyl radical generation in comparison to nonrespirable fly ashes and respirable references. This radical generation was clearly related to the iron mobilization from these particles. In conclusion, the mechanisms by which CFA and the positive references (silica, coal mine dust) affect rat lung epithelial cells seem to be different, and the data suggest that quartz in CFA does not act the same as quartz in silica or coal mine dust. On the other hand, the results indicate an important role for size and iron release in generation and subsequent effects of reactive oxygen species caused by CFA. [ABSTRACT FROM AUTHOR]

An increased incidence of mesothelioma, a malignancy associated with asbestos exposure, was highlighted in some areas of New Caledonia, where ultrabasic units extend for more than a third of the land and economy largely relies on nickel mining activity. Ultramafic rocks exploitation includes, beside nickel, the natural occurrence of chrysotile and tremolite asbestos and asbestiform fibrous minerals, such as fibrous antigorite. In New Caledonia, fibrous antigorite is considered an asbestos by the law, despite limited toxicity assessment is available so far. This work delivers preliminary information on the in vitro toxicity of fibrous antigorite and comparatively discusses results with respect to chrysotile asbestos. Three fibrous antigorite samples, differing by the alteration level and containing about 50% of fibrous particles mostly in respirable size, were compared with chrysotile in terms of physico-chemical properties, cell-free reactivity tests, and cellular toxicity induced in human epithelial cells (A549) and in murine macrophages (MH-S). Samples with alteration grade 2 (low weathering) and 4 (high weathering) exhibited the same reactivity in terms of hydroxyl radicals release of UICC chrysotile, but did not catalyze carbon-centered radical generation and contained smaller amount of bioavailable iron. Weathered antigorite samples were cytotoxic in a dose-dependent manner and induced oxidative stress and a pro-inflammatory intracellular messenger (NO). A similar effect was obtained with chrysotile at 4-times lower dose. Conversely, the non-weathered antigorite (alteration grade 1) showed a very weak surface reactivity and did not trigger any cellular effect. Asbestos toxicity depends on fibrous habit, surface reactivity, and biopersistence. Our tests revealed that fibrous antigorite has a lower reactivity than chrysotile. However, fibrous antigorite showed a leaching kinetics in simulated body fluids slower than chrysotile, suggesting that antigorite biopersistence could be higher than chrysotile. Further research is needed to confirm antigorite higher biopersistence and lower reactivity of unaltered samples, with respect to weathered ones. [ABSTRACT FROM AUTHOR]

Among the physico-chemical features responsible for the so-called “variability of quartz hazard”, a key role has been assigned to the silica surface charge, evaluated by means of ζ potential measurement. The ζ potential of silica describes the protonation state of silanols which, in turn, determine interactions with cell membranes. To gain a molecular understanding of the role of silanols in silica pathogenicity, we conducted a systematic investigation of the variation of the ζ potential as a function of pH (ζ plot titration curve) on a large set of respirable quartz particles with different levels of metal contaminants. The membranolytic activity of the particles on red blood cells, used as a readout of pathogenic activity, was assessed in parallel. Pure quartz surfaces showed sigmoid-shaped ζ plots suggesting the presence of silanol families with similar acidity, whereas contaminated dusts exhibited convex-shaped ζ plots, indicating a higher silanol heterogeneity on contaminated surfaces with respect to the pure ones. The quartz particles with a higher surface heterogeneity related to metal contamination showed a higher membranolytic activity. By removing structural defects and chemical heterogeneity, the ζ plot shifted towards the typical shape of pure quartz and the membranolytic activity was reduced. We conclude that the ζ plot is a useful readout to measure the acid-base behavior of quartz surfaces and to describe the chemical heterogeneity of quartz silanols. Surface heterogeneity, here induced by metal contamination, is proposed as the main cause of quartz membranolytic activity, further supporting the hypothesis that surface silanol disorganization determines silica pathogenicity. [ABSTRACT FROM AUTHOR]

Industrial processing of materials containing quartz induces physico-chemical modifications that contribute to the variability of quartz hazard in different plants. Here, modifications affecting a quartz-rich sand during cast iron production, have been investigated. Composition, morphology, presence of radicals associated to quartz and reactivity in free radical generation were studied on a raw sand and on a dust recovered after mould dismantling. Additionally, cytotoxicity of the processed dust and ROS and NO generation were evaluated on MH-S macrophages. Particle morphology and size were marginally affected by casting processing, which caused only a slight increase of the amount of respirable fraction. The raw sand was able to catalyze OH and CO 2 − generation in cell-free test, even if in a lesser extent than the reference quartz (Min-U-Sil), and shows h Al radicals, conventionally found in any quartz-bearing raw materials. Enrichment in iron and extensive coverage with amorphous carbon were observed during processing. They likely contributed, respectively, to increasing the ability of processed dust to release CO 2 − and to suppressing OH generation respect to the raw sand. Carbon coverage and repeated thermal treatments during industrial processing also caused annealing of radiogenic h Al defects. Finally, no cellular responses were observed with the respirable fraction of the processed powder. [ABSTRACT FROM AUTHOR]