A nested case-control study of 198 lung cancer deaths among a cohort of 12,315 mine workers “showed a strong and consistent relation between quantitative exposure to diesel exhaust and increased risk of dying of lung cancer,” researchers reported in the Journal of the National Cancer Institute.¹ “To our knowledge, this is the first report of a statistically significant exposure–response relationship for diesel exposure and lung cancer based on quantitative estimates of historical diesel exposure with adjustment for smoking and other potential confounders,” the researchers stated.

The mineworkers had been employed in a blue-collar job for at least 1 year after the introduction of diesel equipment into the mining facility. The eight mining facilities where they worked were all in the United States, and “considered to have had high air levels or diesel exhaust underground but low levels of potential occupational confounders (ie, radon, silica, asbestos),” according to the study report

The researchers estimated diesel exhaust exposure, represented as respirable elemental carbon, using extensive retrospective assessment at each mining facility. “We observed statistically significant increasing trends in lung cancer risk with increasing cumulative [respirable elemental carbon] and average [respirable elemental carbon] intensity,” the researchers reported. Workers in the top quartile of exposure had a three times greater lung cancer risk than workers in the lowest quartile.

Study Implications

“Our findings are important not only for miners but also for the 1.4 million American workers and the 3 million European workers exposed to diesel exhaust and for urban populations worldwide,” the authors noted. “Some of the higher average elemental carbon levels reported in cities,” the authors pointed out, include Los Angeles, the Bronx, nine urban sites in China, Mexico City, and Estarreja, Portugal.

“Environmental exposure to average elemental carbon levels in the 2–6 µg/m³ range over a lifetime as would be experienced in highly polluted cities approximates cumulative exposures experienced by underground miners with low exposures in our study. Because such workers had at least a 50% increased lung cancer risk, our results suggest that the high air concentrations of elemental carbon reported in some urban areas may confer increased risk of lung cancer. Thus, if the diesel exhaust/lung cancer relation is causal, the public health burden of the carcinogenicity of inhaled diesel exhaust in workers and in populations of urban areas with high levels of diesel exposure may be substantial.” ■

Reference

1. Silverman DT, Samanic CM, Lubin JH, et al: The diesel exhaust in miners study: A nested case-control study of lung cancer and diesel exhaust. J Natl Cancer Inst 104:855-868, 2012.