Diesel exhaust and lung cancer mortality in potash mining

Findings from experimental studies on rodents and from epidemiological studies suggest that diesel exhaust may cause lung cancer. There is evidence that in several occupations, e.g., truck drivers and railway workers, the risk of lung cancer increases with duration of employment, and exposure to diesel exhaust provides the most likely explanation for these elevations of risk.

We investigated the association between lung cancer mortality and exposure to diesel exhaust in a cohort study. The cohort comprised 5, 536 male potash miners who were followed from 1970 to 1994. Exposure was assessed from concentration measurements of the total carbon (i. e., elemental and organic carbon in total) in personal dust samples. The concentration values were multiplied by years of exposure to give a quantitative exposure measure. The concentration levels ranged from 0.12 to 0.39 mg/m(3) total carbon in fine dust. Work histories and smoking habit data were obtained from medical company records. Causes of death were ascertained from death certificates.

During the follow-up period, 424 deaths were recorded, including 133 of cancer, 38 of lung cancer. The relative risk of lung cancer between two groups with high and low exposure was 2.2 (95% confidence interval 0.8-6.0). With Cox regression, we found a lung cancer relative risk 1.7 (0.5-5.8) after twenty years of exposure. Extensive scrutiny proved smoking not to be a confounder in this study.

The principal finding of the study is a doubling of relative lung cancer risk after twenty years of exposure in the workplaces with highest exposure. However, the observed elevation is nonsignificant even at a 90% level. Further follow-up is intended to enhance the study power.