A critical review of the relationship between occupational exposure to diesel emissions and lung cancer risk

Abstract

In 2012, a working group of the International Agency for Research on Cancer classified diesel exhaust (DE) as a human carcinogen (Group 1). This decision was primarily based on the findings of the Diesel Exhaust in Miners Study (DEMS). The disparity between the results of various methodological approaches applied to the DEMS led to several critical commentaries. An expert panel was subsequently set up by the Health Effects Institute to evaluate the DEMS results, together with a large study in the trucking industry. The panel concluded that both studies provided a useful basis for quantitative risk assessments (QRAs) of DE exposure. However, the results of both studies were non-definitive as the studies suffer from several methodological shortcomings. We conducted a critical review of the studies used by the International Agency for Research on Cancer (IARC) working group to evaluate the relationship between DE and lung cancer. The aim was to assess whether the available studies support the statement of a causal relationship and, secondarily if they could be used for QRA. Our review highlights several methodological flaws in the studies, amongst them overadjustment bias, selection bias, and confounding bias. The conclusion from our review is that the currently published studies provide little evidence for a definite causal link between DE exposure and lung cancer risk. Based on two studies in miners, the DEMS and the German Potash Miners study, QRA may be conducted. However, the DEMS data should be reanalyzed in advance to avoid bias that affects the presently published risk estimates.

Keywords:

• Diesel exhaust
• lung cancer
• epidemiology
• review
• exposure–response
• risk estimation

Acknowledgements

The authors gratefully acknowledge the careful review provided by the anonymous reviewers. We also thank Dr. Norbert Kersten, Dr. Dagmar Pattloch and Anne Pohrt for their helpful comments on an earlier version of this manuscript. Finally, we thank Dr. Clare Barnett for language editing.

Declaration of interest

The employment affiliation of the authors is as shown on the first page. The Federal Institute for Occupational Safety and Health (BAuA) is a German Federal Departmental Research Institute. As a federal authority, it is directly responsible to the Federal Ministry of Labor and Social Affairs (BMAS). It conducts research and development in the field of safety and health at work, promotes the transfer of knowledge into practice, advises policymakers and performs sovereign functions (www.baua.de).

As part of their work activities, the authors act as advisors in several committees in Germany that discuss and provide policy advice on occupational health issues. MM is an advisor for the Permanent Senate Commission for the Investigation of Health Hazards of Chemical Compounds in the Work Area (MAK Commission) which proposes maximum workplace concentrations (MAK values) for volatile chemicals and dusts, biological tolerance values (BAT values), biological guide values (BLW), biological reference values for workplace substances (BAR) and analytical methods for substances in the air and biological material. Substances, which are carcinogenic, germ cell mutagenic, sensitizing or absorbed percutaneously or which pose a risk during pregnancy are classified accordingly (www.dfg.de/en/dfg_profile/statutory_bodies/senate/health_hazards/index.html). MM further is an advisor for the subcommittee “Risk Assessment” (UA III) of the Commission on Hazardous Substances (AGS), which counsels the BMAS on work safety with regard to hazardous substances, including classification and labeling. Evaluation of the risk associated with occupational exposure to diesel motor emissions is a current issue in both committees.

Furthermore, MM and AW provide epidemiologic advice for the Medical Expert Advisory Board Occupational Diseases, which counsels the BMAS on the scientific prerequisites with regard to new legal occupational diseases.

The authors take full responsibility for the analyses, interpretations and conclusions in the present review. The presented ideas and opinions are exclusively those of the authors and do not necessarily reflect those of the mentioned institutions.