Objectives: To estimate the exposure-response function associating polycyclic aromatic hydrocarbons (PAH) exposure and lung cancer, with consideration of smoking.
Methods: Mortality, occupational exposure and smoking histories were ascertained for a cohort of 16,431 persons (15703 men and 728 women) who had worked in one of four aluminium smelters in Quebec from 1950-1999. A variety of exposure-response functions were fitted to the cohort data using generalised relative risk models.
Results: In 677 lung cancer cases there was a clear trend of increasing risk with increasing cumulative exposure to PAH. A linear model predicted a relative risk of 1.35 (95%CI 1.22-1.51) at 100 ug/m 3-BaP-years , but there was a significant departure from linearity in the direction of decreasing slope with increasing exposures. Among the models tried, the best fitting were a two-knot cubic spline and a power curve (RR=(1+bx)p), the latter predicting a relative risk of 2.68 at 100 ug/m 3-BaP-years. Additive models and multiplicative models for combining risks from occupational PAH and smoking fitted almost equally well, with a slight advantage to the additive.
Conclusion: Despite the large cohort with long follow-up, the shape of the exposure-response function and the mode of combination of risks due to occupational PAH and smoking remains uncertain. If a linear exposure-response function is assumed, the estimated slope is broadly in line with the estimate from a previous follow-up of the same cohort, and somewhat higher than the average found in a recent meta-analysis of lung cancer studies.
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