Abstract

Studies in railroad workers, truck drivers, and miners reveal diesel exhaust to be carcinogenic. Although technology has evolved, a large capacity in the U.S and globally still comprises traditional diesel engine design in transportation, mining, construction and farming. The Diesel Exhaust in Miners Study (DEMS) with an extensive exposure assessment investigated 200 lung cancer deaths in non-coal and non-metal miners. A DEMS dataset was used to calculate the excess lifetime risk for airborne concentrations of respirable elemental carbon (REC). A healthy worker survivor effect and possible confounding by non-diesel power generation and other mining exposures (e.g., explosives) were investigated along with dose-rate effects using Poisson regression methods with high-resolution classification. Lung cancer mortality declined with employment duration and more so when REC and non diesel exposure effects were also estimated, revealing a strong survivor bias. Attenuation of the REC effect was also observed with increasing (lagged) cumulative REC exposure. In underground miners, the excess relative rate of lung cancer mortality was 0.67 (p < 0.0001) for a 10 year exposure to 200 µg/„m³ REC, a typical underground exposure. At occupational REC exposures of 200, 10 and 1 µg/m³ the excess lifetime risks, respectively, were 119, 43 and 8.7 per thousand. The estimated lifetime risk was greater than some previous estimates not accounting for heathy worker survival bias. This bias was addressed using employment duration and mine above/below ground status. A model-fitted function of cumulative exposure accommodated attenuation of exposure effect. The estimated excess lifetime risks of lung cancer at old diesel REC exposure levels common in occupational groups in the past exceed 5%.