Petroleum Asphalt Inhalation by Mice

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Abstract
The effect on the tracheobronchial tree and lungs of 20 C57 black mice inhaling an aerosol of petroleum asphalt and another group of 30 mice inhaling smoke from heated petroleum asphalt were studied. The most frequent changes were peribronchial infiltration of round cells, bronchial dilatation, and destruction and atrophy of the epithelium. Thickening of the alveolar septa and emphysema were seen occasionally. Squamous metaplasia was infrequent but hyperplasia occurred. The changes were characterized by variability with respect to length of exposure and location of the lesion in each animal. If any generalization can be made regarding the changes in the lungs of these mice, it is the reduction in the amount of functional respiratory tissue. This is accomplished by a variety of pathological changes enumerated under "Results." The findings reported here sufficiently parallel those reported by others for the inhalation of cigarette smoke, artificial smog, and other air pollutants, so as to suggest the possibility that the changes in the tracheobronchial tree and lungs are only loosely related to the composition of the inhaled material. The concordance of findings by all investigators on the effects of air pollutants containing aromatic polycyclic hydrocarbons supports the suspicion that the changes are a general phenomena caused by the nonspecific irritating effect of the entire class of chemicals when inhaled over a long time. C 57 black mice were subjected to inhalation of a petroleum asphalt aerosol. In a second experiment mice breathed the smoke from boiling asphalt. Microscopic examination of the tracheobronchial tree and lungs was made when possible. In the first experiment, changes were minimal. Congestion, acute bronchitis, pneumonitis, bronchial dilatation, and some peribronchiolar round cell infiltration were the changes occasionally seen. In the second experiment, peribronchial round cell infiltration, bronchitis, pneumonitis, abscess formation, loss of cilia, epithelial atrophy, and necrosis were common. Squamous cell metaplasia was rare but hyperplasia was more commonly seen. In both experiments pathological changes were patchy and some animals were relatively refractory to treatment. The changes seen closely parallel those described in other studies of the effects of different air pollutants. The changes in the tracheobronchial tree and lungs of mice breathing air polluted with aromatic polycyclic hydrocarbons may be a general phenomenon and the degree of change is dose dependent.