The toxicological response of Brazilian chrysotile asbestos : A multidose sub-chronic 90-day inhalation toxicology study with 92 day recovery to assess cellular and pathological response.Inhal Toxicol.,18

Inhalation toxicology studies with chrysotile asbestos have in the past been performed at exceed-ingly high doses without consideration of fiber number or dimensions. As such, the exposures have exceeded lung overload levels, making quantitative assessment of these studies difficult if not impossible. To assess the cellular and pathological response in the rat lung to a well-characterized aerosol of chrysotile asbestos, a 90-day subchronic inhalation toxicology study was performed using a commercial Brazilian chrysotile (CA 300). The protocol was based on that established by the European Commission for the evaluation of synthetic vitreous fibers. The study was also designed to assess the potential for reversibility of any such changes and to permit association of responses with fiber dose in the lung and the influence of fiber length. Wis-tar male rats were randomly assigned to an air control group and to 2 CA 300 exposure groups at mean fiber aerosol concentrations of 76 fibers L> 20 µm/cm3 (3413 total fibers/cm3; 536 WHO fibers/cm3) or 207 fibers L> 20 µm/cm3 (8941 total fibers/cm3; 1429 WHO fibers/cm3). The animals were exposed using a flow-past, nose-only exposure system for 5 days/wk, 6 h/day, during 13 consecutive weeks (65 exposures), followed by a subsequent nonexposure period last-ing for 92 days. Animals were sacrificed after cessation of exposure and after 50 and 92 days o