The lung cancer mortality of 5406 men (cohort 1) employed at one aluminum smelter on January 1, 1950, and of 485 men employed at a second plant (cohort 2) on January 1, 1951, is reported. For each man, the total number of years of exposure to tars, number of years since first exposure to tars and an index of exposure to tars expressed in tar-years were calculated.
More than 99% of the men in the first cohort and just less than 98% of the men in the second cohort were traced. As of December 31, 1973, 1070 men in cohort 1 had died and death certificates were obtained for 990 men (92.5%). As of December 31, 1973, 64 men in cohort 2 had died and death certificates were obtained for 58 (91%). There were 84 deaths from lung cancer in cohort 1 and 11 in cohort 2. The results showed that the mortality from lung cancer of that portion of the cohorts 1 and 2 combined who had ever been exposed to tars was similar to that of workers never exposed to tars. The mortality from lung cancer of men in cohort 1 was greater than that expected at Quebec provincial rates, but this was probably due to slightly increased lung cancer mortality in the communities serving the industries. Although the total number of cases in cohort 2 was small the lung cancer mortality was well in excess of that expected at Quebec rates and could not be explained on community experience.
There was a definite dose-response relationship between lung cancer mortality and tar-years and years of exposure. The standardized mortality ratio for persons exposed for more than 21 years to the higher levels of tars was 2.3 times that of persons not exposed to tars. Although smoking may still be a factor, the evidence suggests that the increased risk of lung cancer is related to employment in definite tar-exposed occupations.