Chronic toxicity of tar from heavy-duty diesel exhaust following intratracheal instillations to the lungs of hamsters

Chronic toxicity of tar from heavy-duty diesel exhaust (HD tar) was studied in male Syrian golden hamsters which received 15 mg, 7.5 mg or 1.5 mg of HD tar as the total dosages by intratracheal instillations once a week for 15 weeks. As a control group, hamsters were treated with the 0.1 ml of Tween 60: ethanol: phosphate buffer (pH 6.88, 0.25 M) solution (5.8: 8.7: 100 by volume) once a week in the same manner. The survival rate during the instillation period in the group given 15 mg of HD tar, the high-dose group of HD tar, was the lowest, and the effect was dose-dependent. However, the survival rates during the subsequent observation period showed no marked differences among HD tar treated groups. During their total life span, one papilloma in the larynx was seen in the 44 hamsters in the group given 1.5 mg of HD tar, one papilloma in the larynx was appeared in the 59 hamsters in the group given 1.5 mg of HD tar and one lung adenoma was developed in the 58 hamsters in the control group. There were no tumors in the respiratory tract in the group given 7.5 mg of HD tar. Concerning the histopathological findings of the lung, the incidence of alveolar cell or bronchiolar cell hyperplasia in the group given 1.5 mg of HD tar was significantly higher than that in the control group. From these results, although we could not observe any tumorigenicity or carcinogenic effect of HD tar, it would seem that HD tar caused weak but positive damage to the lungs of hamsters.