Pulmonary Bioassay Studies with Nanoscale and Fine-Quartz Particles in Rats: Toxicity is Not Dependent upon Particle Size but on Surface Characteristics

Pulmonary toxicology studies in rats demonstrate that nanoparticles are more toxic than fine-sized particles of similar chemistry. This study, however, provides evidence to contradict this theory. The aims of the study were (1) to compare the toxicity of synthetic 50 nm nanoquartz I particles versus (mined) Min-U-Sil quartz ( approximately 500 nm); the toxicity of synthetic 12 nm nanoquartz II particles versus (mined) Min-U-Sil ( approximately 500 nm) versus (synthetic) fine-quartz particles (300 nm); and (2) to evaluate the surface activities among the samples as they relate to toxicity. Well-characterized samples were tested for surface activity and hemolytic potential. In addition, groups of rats were instilled with either doses of 1 or 5 mg/kg of carbonyl iron (CI) or various alpha-quartz particle types in phosphate-buffered saline solution and subsequently assessed using bronchoalveolar lavage fluid biomarkers, cell proliferation, and histopathological evaluation of lung tissue at 24 h, 1 week, 1 month, and 3 months postexposure. Exposures to the various alpha-quartz particles produced differential degrees of pulmonary inflammation and cytotoxicity, which were not always consistent with particle size but correlated with surface activity, particularly hemolytic potential. Lung tissue evaluations of three of the quartz samples demonstrated "typical" quartz-related effects--dose-dependent lung inflammatory macrophage accumulation responses concomitant with early development of pulmonary fibrosis. The various alpha-quartz-related effects were similar qualitatively but with different potencies. The range of particle-related toxicities and histopathological effects in descending order were nanoscale quartz II = Min-U-Sil quartz > fine quartz > nanoscale quartz I > CI particles. The results demonstrate that the pulmonary toxicities of alpha-quartz particles appear to correlate better with surface activity than particle size and surface area.