A study of the short-term retention and clearance of inhaled asbestos by rats, using U.I.C.C. standard reference samples.

Rats have been dosed over a 6-week period with U.I.C.C. standard reference samples of amosite, crocidolite and chrysotile A, each at three concentrations: 1,5 and 10 mg/m3. Mass concentrations in the exposure chambers were monitored daily. Because the M.R.E. gravimetric sampler was found to undersample some of these dusts at high concentrations, a sampler with a vertical elutriator was developed. Data on other physical parameters of the dust clouds were also obtained and it was found that the fibre number (greater than 5 micron in length) vs. mass correlation varied markedly between asbestos varieties. After dusting, the rats were sacrificed in five batches over a period of 4 months. The lungs of some animals were retained for pathological examination. This did not reveal any fibrosis although large numbers of fibres were visible, mostly within alveolar macrophages. The remaining lungs were analysed for their asbestos contents by a method based upon infrared spectrophotometry. The clearance data confirm earlier published reports that for rats dosed at similar mass concentrations of chrysotile and amphibole, those dosed with chrysotile retain considerably less dust in their lungs. The data also suggest that the retention and clearance of amphibole abestos may be dose related. Some mathematical treatment of the clearance data has been undertaken.