The fibrogenic activity and neurotoxicity of heat-treated chrysotile.

Thermal degradation of heated chrysotile results in dehydration and changes in its crystalline structure. The impact of heat treatment at 150-1200 degrees C on the biological activity of chrysotile was tested in rats. Heating the chrysotile produced an increase in its biological aggressiveness measured in terms of animal survival rate and fibrogenic activity after intratracheal administration of the dust. The highest death rate (100% of the animals) was noted after administration of chrysotile heated at 600 degrees C. Moreover, increased fibrogenic activity of chrysotile heated at 150 degrees C up to 800 degrees C was found. The biological effect of chrysotile heated at 1200 degrees C did not differ from the effect exerted by unheated chrysotile. After intraperitoneal administration of the dust, the most violent reaction could be observed when chrysotile dust was heated at 600 degrees C, which resulted in symptoms of nervous system impairment (of the hind legs, no reaction to nociceptive stimuli, drop of internal body temperature) and death of the test animals. In male rats, the period between dust administration and the manifestation of symptoms and death was found to be longer than in females.