Inhalation experiments on retention and lung clearance of asbestos in combination with cigarette-smoking

Rats received nose-only exposure to 11,4 mg/m3 UICC crocidolite and 2,5mg/m3 UICC chrysotile A for 2 hours a week for a period of up to 1 year. One-half of the animals also inhaled cigarette smoke, diluted 1:5 with filtered air, twice daily for 34 minutes at a time, 5 days a week. Long-term lung clearance of a radioactively labeled aerosol was determined after 2 and 9 months of exposure. Cigarette smoking decreased lung clearance of inhaled labeled particles. After 2,6 and 12 months of exposure the animals were sacrificed, and organs were ashed in a low-temperature ashing furnace. The number of fibers, and their length and diameter distribution, were examined in both tissue samples and in samples of exposure chamber air, using a scanning electron microscope. Results showed a factor-of-two increase of crocidolite fibers in the lungs of groups also exposed to cigarette smoke, compared to the animals that did not inhale cigarette smoke. No such effect of cigarette-smoking was found on chr ysotile fiber retention. The difference between these results may be due to the different deposition patterns of the two fiber types.