Longitudinal study of workers in an aluminum smelter.

We conducted a 6-y follow-up study that included workers in an aluminum smelter in British Columbia. Of the original cohort, 951 workers left the industry and 985 workers participated in both studies. Comparison of those who left and those who remained showed that those who left were (1) older, (2) had a slightly higher prevalence of respiratory symptoms, and (3) had lower lung function; this was especially true for workers who were 50 + y of age at the time the initial study was conducted. Analyses were conducted only on 586 male workers who did not change their job location or smoking habits between the initial and the follow-up study. Potroom workers in the "high-exposure" group had a significant reduction in the prevalence of cough, but experienced an increase in the prevalence of wheeze. There was no significant difference in the annual decline in forced expiratory volume in 1 sec and forced vital capacity between the potroom workers and controls. In general, older workers and smokers had a greater decline in lung function compared to younger workers and nonsmokers. Leukocyte count done during the initial study was found to be an independent predictor of longitudinal decline in lung function. The lack of exposure effect on longitudinal decline in lung function could be due to "healthy worker" effect and improvement in the working condition of the smelter.