Risk assessment for conventional diesel exhaust (before 1990) and lung cancer in a cohort of miners

Diesel exhaust in the latter half of the 20th century has been found to be a lung carcinogen. Conventional diesel emissions continue in the transportation, mining, construction, and farming industries. From the Diesel Exhaust in Miners Study, a public-use dataset was used to calculate the excess lifetime risk of lung cancer associated with diesel exposure (1947-1997). Excess rates of lung cancer mortality associated with respirable elemental carbon (REC) and possible other mining exposures (e.g., oil mists, explosives emissions) were investigated using Poisson regression methods. Lung cancer mortality declined with increasing employment duration while increasing with cumulative REC and non-diesel exposures, suggesting a strong worker survivor effect. Attenuation of the REC effect was observed with increasing cumulative exposure. After adjustment for employment duration, the excess rate ratio for lung cancer mortality was 0.67 (95% CI = 0.35-0.99) for a 10-year lagged exposure to 200 μg/m³ REC, a typical below-ground exposure in the study mines. At exposures of 200, 10, and 1 μg/m³ REC, the estimated excess lifetime risks, respectively, were 119, 43, and 8.7 per thousand. Analysis of an inception cohort hired after dieselization commenced produced smaller and less certain estimates of lifetime risk. From exposures to conventional diesel engine exhaust common in occupational groups in the past, the excess lifetime risk of lung cancer was more than 5%. Ambient REC exposures in the general population were estimated to confer lifetime risks of 0.14 to 14 per thousand, depending on assumptions made.