Diesel exhaust in the occupational setting. Current understanding of pulmonary health effects

Doll's landmark 1959 study of the epidemiology of occupational lung cancer failed to find an increased risk in workers exposed to petrol fumes and emissions. In it, he pointed out a critical issue that is not resolved today. With theoretically increased risk based on biological plausibility but an absence of positive findings, epidemiologic methodology cannot reliably distinguish between no risk and very little risk. Despite the ensuing nearly 40 years of research, neither human epidemiologic studies nor animal studies can support a causal relationship between either lung cancer or noncancer respiratory health effects at current levels of occupational exposure. Even with statistically significant but low relative risks, neither evidence of causality nor level of risk can be definitively established. Epidemiologic data suggest that an increased risk of lung cancer for diesel exhaust exposed workers may be comparable with that for environmental tobacco smoke. Monitoring and control of the particulate is necessary. Prudent policy dictates continued efforts to reduce emissions of soot from diesel engines and decrease occupational exposure as a matter of good health and safety practice. Improvements in engine design, soot filters, and fuel modification will provide the best approach to exposure control. Further research is also needed in the areas of carcinogenic mechanisms and development and validation of biomarkers of exposure before reliable estimates of risk of human health effects in the occupational setting can be made.