Does the crystal habit modulate the genotoxic potential of silica particles? A cytogenetic evaluation in human and murine cell lines

Crystalline silica inhaled from occupational sources has been classified by IARC as carcinogenic to humans;in contrast, for amorphous silica, epidemiological and experimental evidence remains insufficient. Thegenotoxicity of crystalline silica is still debated because of the inconsistency of experimental results(“variability of silica hazard”), often related to the features of the particle surfaces. We have assessedthe role of crystal habit in the genotoxicity of silica powders. Pure quartz (crystalline) and vitreous silica(amorphous), sharing the same surface features, were used in an in vitro study with human pulmonaryepithelial (A549) and murine macrophage (RAW264.7) cell lines, representative of occupational andenvironmental exposures. Genotoxicity was evaluated by the comet and micronucleus assays, and cyto-toxicity by the trypan blue method. Cells were treated with silica powders for 4 and 24 h. Quartz but notvitreous silica caused cell death and DNA damage in RAW264.7 cells. A549 cells were relatively resistantto both powders. Our results support the view that crystal habit per se plays a pivotal role in modulatingthe biological responses to silica particles.