Relationship between Surface Properties and Cellular Responses to Crystalline Silica:  Studies with Heat-Treated Cristobalite

Abstract

A fibrogenic sample of cristobalite dust, CRIS (crystalline silica of mineral origin), was heated to 1300 degrees C (CRIS-1300) to relate induced physicochemical modifications to cytotoxicity. Heating did not affect dust micromorphology and crystallinity, except for limited sintering and decreased surface area of CRIS-1300. Thermal treatments deeply affected surface properties. Electron paramagnetic resonance showed surface radicals progressively annealed by heating, mostly disappearing at >/=800 degrees C. Surface hydrophilicity or hydrophobicity, evaluated with water vapor adsorption, still showed some hydrophilic patches in CRIS-800, but CRIS-1300 was fully hydrophobic. Heating modified the biological activity of cristobalite. Cytotoxicity, tested on proliferating cells of the mouse monocyte macrophage cell line J774, showed that CRIS was cytotoxic and CRIS-800 was still cytotoxic, but CRIS-1300 was substantially inert. Cytotoxicity of CRIS to the rat lung alveolar epithelial cell line, AE6, as measured by colony forming efficiency, was greatly reduced for CRIS-800 and eliminated for CRIS-1300. The rate of lactate dehydrogenase release by rat alveolar macrophages was lowered for CRIS-800, and release was completely inactivated for CRIS-1300. The absence of surface radicals and the onset of hydrophobicity may both account for the loss of cytotoxicity upon heating. Differences observed between CRIS-800 and CRIS-1300, both fully deprived of surface radicals, indicate that hydrophobicity is at least one of the surface properties determining the cytotoxic potential of a dust.

Silica Surface Features and Their Role in the Adsorption of Biomolecules: Computational Modeling and Experiments

“…606 The formation of a stable water monolayer on flat surfaces was later confirmed by ab initio works which characterized the water monolayer on crystalline surfaces as e.g. Q(0001) 542,554,574,576,590 ( Figure 46ab) and C (100) (Figure 47a).…”

Marine diatom growth on different forms of particulate silica: evidence of cell/particle interaction

“…Hydrophilic quartz (Min-U-Sil 5, Berkeley Springs Plant, ITC) is a highly pure commercial dust (SiO 2 , 98.7%) obtained by crushing quartz crystals: the grinding process causes the exposure of fresh surfaces with a high reactivity due to the presence of surface radicals and trace metal impurities. Such quartz particles (mean diameter 1.7 µm) are characterized by a high hydrophilicity due to the abundance of silanols at the surface, generated by the contact of water vapour with the newly formed surfaces (Fubini et al 1999). Hydrophobic quartz dust is obtained from the above hydrophilic quartz by heating it to 800 ± 1°C in a quartz container connected to a vacuum line.…”

“…The order of diatom growth, in fact, recalls the effect caused by molecules containing a planar diol moiety such as ascorbic acid and catechol, which increase the solubility of crystalline silica more than the amorphous silica substrates (Bennet 1991, Fubini et al 1999. To demonstrate the possible involvement of a similar mechanism, the solubility of the various particulate silica substrates was measured in the presence of ascorbic acid and catechol in a cell-free system in the same culture medium condi- tions used for diatoms.…”

High-resolution 3D analyses of the shape and internal constituents of small volcanic ash particles: The contribution of SEM micro-computed tomography (SEM micro-CT)

“…The morphology of particles also comes into play when considering health hazards (Blong, 1984) such as eye irritation and respiratory ailments, because the bio-reactivity of particles, mainly imputable to the presence of surface radicals (Horwell et al, 2003), increases along with the surface-to-volume ratio (Fubini et al, 1999;Tran et al, 2000;Hetland et al, 2001). Furthermore, the morphology of ash particles is a concern when dealing with aircraft safety (Casadevall, 1994) and infrastructure damage (Blong, 1984), as the abrasive power of ash is a function of angularity (Stachowiak, 2000).…”