Chronic Inhalation of Short Asbestos: Lung Fiber Burdens and Histopathology for Monkeys Maintained for 11.5 Years after Exposure

In an earlier report, presented the results of an 18-month inhalation exposure of rats and monkeys to short chrysotile asbestos. The mean chamber exposure level was 1.0 mg/m3with an average of 0.79 fibers/ml > 5 μ m in length. Gross and histopathological examination of exposed and control rats indicated no treatment-related lesions. Asbestos bodies adjacent to the terminal bronchioles, but no fibrosis, were found in lung biopsy tissue taken from the exposed monkeys at 10 months post-exposure. Fifteen monkeys (9 exposed and 6 controls) from this study were maintained for 11.5 years following exposure. Lung fiber burdens were determined by transmission electron microscopy. The mean lung burden (± standard deviation) for 59 samples from exposed monkeys was 63 ± 30× 106 fibers/g dry lung (range, 18–139 × 106). The geometric mean fiber length was 3.5 μ m with 35% of the fibers being > 5 μ m in length. These data indicate some chrysotile fibers are durable in vivo for a significant period of time. Lungs were ex...