Experimental studies on the effects of heated chrysotile asbestos and automobile brake lining dust injected into the body cavities of mice

A series of experiments with mice involving the intrapleural injection of chrysotile asbestos dust heated to varying temperatures up to 1000°C suggests that the physical shape of the dust particles is more important than the altered chemistry of the dust. Chrysotile heated to no more than 400°C produced dust samples containing many long fibers, and these samples resulted in large pleural granulomas. Chrysotile heated to more than 400°C produced dust containing mainly particles of low aspect ratio, and these produced very small granulomas. The initial size of the granulomas was very closely related to the final degree of fibrosis found in the animals and, therefore, chrysotile heated to 400°C or less was much more fibrogenic than when it was heated to higher temperatures. A sample of automobile brake lining dust was found to contain very little recognizable chrysotile, and consisted mainly of particles with a low aspect ratio. When this dust was injected into the pleural cavities of mice it produced very small granulomas and little fibrosis.