Smoking inhibits asbestos clearance.

To determine whether smoking affects the clearance of asbestos fibers, guinea pigs were given amosite asbestos by intratracheal instillation and divided into 3 groups: (1) nonsmokers, (2) animals exposed to smoke only after asbestos instillation, and (3) animals exposed to smoke both before and after asbestos instillation. Asbestos fiber concentrations and sizes were measured at 1 wk and 1 month after exposure. Between 1 wk and 1 month the asbestos burden in nonsmokers decreased on average 6-fold, whereas both smoking groups failed to show a significant decrease. Over this time period, the mean length of retained fibers increased in the nonsmokers but decreased in both smoking groups. This phenomenon was seen in tissue samples and lavage samples, although lavaged fibers were consistently shorter than tissue fibers. We conclude that in this model, cigarette smoking impedes asbestos clearance, largely by increasing retention of short fibers. This increased pulmonary fiber burden may be important in the increased disease rate seen in asbestos workers who smoke.