Comment: Carcinogenicity of diesel-engine exhaust (DE)

Abstract

In June 2012, a working group of 24 experts convened by the section of monographs (IMO) of the International Agency for Research on Cancer (IARC) concluded ‘‘that there was ‘sufficient evidence’ in humans for the carcinogenicity of diesel-engine exhaust (DE)’’ (Benbrahim-Tallaa et al. 2012). It must be noted that this evaluation statement applies generally to all kinds of DE as there are no exceptions defined. Two of us, DP and PM, were present as IMO meeting observers. We believe that relevant issues for a thorough evaluation of DE remained unaddressed in the preliminary publication that is available in Lancet Oncology (Benbrahim-Tallaa et al. 2012), and therefore, we intend to stimulate further discussions on this important public health issue. As Lancet Oncology does not publish letters or comments on news articles, we thank the Editor of Archives of Toxicology to provide the opportunity to publish this Comment. First of all, it must be noted that the conclusion of ‘‘sufficient evidence’’ for the carcinogenicity of DE is mainly based on selected epidemiological studies evaluating traditional DE (Benbrahim-Tallaa et al. 2012), which has the following implications. The publication on the US miners study states: ‘‘Initial (i.e., a priori defined) analyses from the complete cohort did not reveal a clear relationship of lung cancer mortality with DE exposure’’ (Attfield et al. 2012). Although the SMR for surface-only workers was higher than for everunderground workers (1.33 vs. 1.21), mean DE exposures were about 75-fold higher in ever-underground workers. However, further analyses for the complete cohort associating an increased lung cancer risk with higher DE exposures—even in the case–control study—were conditional on a mean hazard ratio for surface-only versus everunderground work of 1.9 (Attfield et al. 2012; Silverman et al. 2012). Since other possible exposures were considered to be negligible, it is unclear which risk factors could explain such different risks between the workers at these two locations. Both US miners study papers (Attfield et al. 2012; Silverman et al. 2012) suffer from weaknesses in exposure assessment, based on respirable elemental carbon (REC) measurements in 1998–2001 for workers employed between 1947 and 1997. The REC exposure assessment was mainly based on a correlation between CO and REC measurements (Vermeulen et al. 2010). The authors commented ‘‘...that the observed coefficient derived from this cross-sectional study might not apply longitudinally to past conditions.’’ Moreover, Crump and van Landingham D. Pallapies (&) D. Taeger Institute for Prevention and Occupational Medicine, German Social Accident Insurance, Institute of the Ruhr-University Bochum (IPA), Burkle-de-la-Camp-Platz 1, 44789 Bochum, Germany e-mail: pallapies@ipa-dguv.de