Fate and effect of inhaled chrysotile asbestos fibres.

An effective assessment of the relative toxicity of inhaled fibres requires an understanding of the rates of deposition and clearance, and of chemical or morphological changes which occur in fibres under the biochemical conditions of the lung. Although fibres of amphibole asbestos remain virtually unchanged after many years of residence in the lung, chrysotile fibres split longitudinally and leaching of both structural and trace elements occurs. In the experiments described, rats were exposed to airborne UICC chrysotile asbestos at 10 mg m −3 for 7 h per day, 5 days per week for periods of up to 18 months. During the exposure, groups of rats were killed at predetermined times, their lungs digested, the retained chrysotile fibres recovered, then counted and sized by scanning electron microscopy. The results showed that splitting of chrysotile fibres led to the number of long thin fibres in the lung increasing with time. The data describing the accumulation of chrysotile fibres, combined with the available evidence on the effects of the leaching of structural elements, provide an improved basis for interpreting the pathogenic effects of this fibre.