Toxicity of a quartz with occluded surfaces in a 90-day intratracheal instillation study in rats

This 90-day study was aimed at characterizing the differences in biological activity between a crystalline ground reference quartz (DQ12) and a quartz with occluded surfaces (quartz isolate) obtained from a clay deposit formed 110 to 112 million years ago. In different test groups, rats were dosed with the same total mass and quartz level by intratracheal instillation, with a total high dose of 15.2 mg/kg (body weight, bw) or approximately 4.7 mg/rat of each quartz species in a saline suspension. The reference quartz was mixed with titanium dioxide to achieve a positive control mixture, which contained the same quartz content as in the quartz isolate. At 3 days post dosing, both quartz groups showed a significant inflammatory response based on total and differential cell counts from bronchoalveolar lavageate (BAL) analysis. At 28 and 90 days, the quartz isolate values were no longer statistically different from vehicle control group values; however, the positive control group values were approximately 12 and 65 times greater than those of the control group, respectively. After 28 days, histopathological evaluation showed moderate effects in the quartz isolate group compared to the saline control animals. These effects did not progress in severity at 90 days. In contrast, the positive control group exhibited more severe effects than the quartz isolate group and these effects showed a progression to a persistent and self-perpetuating inflammatory state. The toxicological properties of quartz particles can vary significantly dependent on their surface characteristics. Toxicity can range from a high-dose-induced, modest, transient inflammation from quartz with occluded surfaces, to a severe and persistent inflammatory state caused by ground quartz with fractured surfaces.