non-ferrous smelter: the role of cadmium

Lung cancer mortality was examined in a cohort of 4393 men employed at a zinc-leadcadmium smelter. There was an excess oflung cancer (overall SMR = 124-5, 95% confidence interval 107-144) which was particularly evident for those employed for more than 20 years. A statistically significant trend in SMRs with increasing duration of employment was apparent. Quantitative estimates of exposure to cadmium and ordinal rankings for lead, arsenic, zinc, sulphur dioxide, and dust were used to calculate cumulative exposures from job histories. Matched logistic regression was used to compare the cumulative exposures of cases of lung cancer to those of controls matched for date of birth and date of starting work and surviving at the time of death of the matched cases. The increasing risk of lung cancer associated with increasing duration of employment could not be accounted for by cadmium and did not appear to be restricted to any particular process or department. Although lung cancer mortality was associated with estimates ofcumulative exposure to arsenic and to lead, it was not possible to determine whether the increased risk might be due to arsenic, lead, or to other contaminants in the smelter. These results are compared with findings from other non-ferrous smelters. In a study on the mortality of workers exposed to cadmium a cohort of almost 7000 men born before 1940 and exposed to cadmium for at least one year before 1970 was followed up until the end of 1979 by Armstrong and Kazantzis.' By contrast with the findings in some other studies,23 the cohort showed no excess mortality from prostatic cancer.'4 Nevertheless, a small but significant excess mortality from lung cancer was observed in men employed for more than ten years (standardised mortality ratio (SMR) 126, 95% confidence interval (CI) 102-153). The absence of any relation to intensity ofexposure, in contrast to the large excess mortality from chronic bronchitis where a significant dose response relation was observed, led to the conclusion that the excess lung cancer mortality was unlikely to be related to past exposure to cadmium. Subsequently, a high incidence oflung cancer in rats dosed with a cadmium chloride aerosol was reported by Takenaka et al5 and Thun et al 6 found a significant excess mortality from lung cancer in smelter workers *Present address: Department of Paediatric Epidemiology, Institute of Child Health, 30 Guilford Street, London WCIN 1 EH. Accepted 3 August 1987 exposed to cadmium, with evidence of a dose response relationship.6 It was therefore decided to make a further study of lung cancer (ICD 8th revision 162-01629) in the cohort described by Armstrong and Kazantzis.' Attention was restricted to a large nonferrous smelter (identified as cohort Cl. 1 in the study by Armstrong and Kazantzis4) which comprised 64% of the entire cohort for which job/exposure data for cadmium were already available from this previous study, requiring only the collection of information to control for exposure to other contaminants. SMRs were calculated to assess mortality in the smelter as a whole. To examine the contribution of specific departments, processes, and contaminants in the smelter a matched case-control analysis was performed.