[Biological effect of fibrous mineral dust. I. Fibrogenic properties of the products of the thermal degradation of chrysotile].

Chrysotile asbestos samples, on comminution, were exposed to temperatures typical for asbestos products exploitation. Subsequently, in an experiment on white rats the effects of temperature upon asbestos fibrous effects were evaluated. The highest aggressiveness was that of the sample heated at 600 degrees C. All the animals died as soon as 50 or 25 mg of dust had been administered intratracheally. Only 3 samples could be administered intratracheally at a dose of 50 mg: non-heated. heated at 400 degrees C and heated at 800 degrees C samples. The doses heated at 400 and 800 degrees C had be reduced by half. Samples heated at 150 to 800 degrees C induced higher hydroxyproline increases than the non-heated sample. The fibrogenic activity of the dust heated at 1200 degrees C was very similar to the fibrogenic activity of the non-heated dust.