Effect of micromorphology and surface reactivity of several unusual forms of crystalline silica on the toxicity to a monocyte-macrophage tumor cell line

The fibrogenic or carcinogenic response to the inhalation of crystalline si lica dusts is strictly related to the physicochemical properties of the par ticles, which, in turn, are mostly determined by the "origin" and the histo ry of the dust. Several physicochemical properties I,ave been reported to m odulate silica pathogenicity. None of them simply correlate with the report ed toxicity in ali the systems used to study silica pathogenicity This conf irms, on the one hand, that several properties are implicated at the same t ime, and on the other that pathogenicity is the result of a multistage proc ess. There is a general consensus on the key role played by alveolar macrop hages in silica-related diseases. For this article the cytotoxicity of a la rge variety of silicas, including rather unusual forms, with controlled mic romorphology and surface properties, has been studied on a mouse monocyte-m achrophage tumor cell line successfully employed in previous studies on cri stobalite (Fubini el al., 1999). When com pared on a per unit surface basis , crystalline silicas were more cytotoxic than amorphous ones, with the not able exception of stishovite, the nonpathogenic crystalline polymorph, with octahedrally coordinated silicon atoms. Among the amorphous ones, a diatom aceous earth and a powdered silica glass exhibited an intermediate toxicity higher than what was elicited by a pyrogenic silica. In this study a new c lass of crystalline silicas have been considered, pure-silica zeolites, whi ch constitute a new morphological entity with which cells may be confronted . The cytotoxicity of these samples varies from inert to highly cytotoxic, covering all the range of toxicity covered by the traditional silica dusts. We discuss the influence of morphological properties and surface reactivit y on the cytotoxicity of several pure-silica zeolites. The extent of expose d surface and the shape of the particles correlate with cell toxicity The l ower cytotoxicity of one "non-pathogenic quartz" and of an aluminum-coated Min-U-Sil quartz, compared with the original pathogenic Min-U-Sil quartz, s uggest a depressive effect of the aluminum ions present at the surface of b oth quartzes. The extreme variability in the biological response to crystal line silicas is confirmed and a new class of materials is brought to the st udy of the mechanisms of silica pathogenicity.