Re: Seidler A, Jänichen S, Hegewald J et al. Systematic review and quantification of respiratory cancer risk for occupational exposure to hexavalent chromium

Abstract

The review of Seidler and colleagues aimed at assessing the dose–response relation for occupational exposure to hexavalent chromium (Cr (VI)) and lung cancer in order to establish a risk-based occupational exposure limit (OEL) for Germany that currently lacks a binding threshold value (Seidler et al. 2012). The authors concluded that the excess risk could be ‘‘acceptable’’ (\4 cases/10.000 workers assuming 40 years of exposure) at 0.1 lg Cr(VI)/m or 4 lg Cr(VI)/m 9 years as lifetime exposure and may become ‘‘intolerable’’ beyond 1 lg/m or 40 lg/m 9 years, respectively. Although there are many industrial processes with exposure to Cr(VI), the assessment of Seidler and colleagues was only based on two historical cohorts in the US chromate industry (further referred to as Baltimore and Painesville cohort) (Gibb et al. 2000; Park et al. 2004; Crump et al. 2003; Luippold et al. 2003). Seidler et al. (2012) recognized this limitation but refrained from a discussion of risk estimates after major process changes and in other exposure circumstances like welding. Notably, no excess risk was observed at lower Cr(VI) concentrations in new chromate plants (Luippold et al. 2005). Welders comprise a considerably larger workforce exposed to Cr(VI) than chromate-producing workers. The excess risk presented by OSHA (U.S. Occupational Safety and Health Administration) for the IARC study in welders (Gerin et al. 1993) was lower than in chromate workers (OSHA 2006). These two chromate cohorts had been already subjected to previous risk assessments (e.g. (Goldbohm et al. 2006; Park and Stayner 2006)) and were preferred by OSHA in the determination of the permissible exposure limit (OSHA 2006). It is noteworthy that at least 80 % of the workers were smokers and that only four out of the 122 lung cancer cases of the Baltimore cohort were never smokers. Therefore, regression models had been applied to the individual exposure and covariate data to adjust relative risks for smoking (Gibb et al. 2000, Crump et al. 2003). OSHA’s risk assessment also refers to re-analyses of the original data with attempts to adjust for smoking or to exclude short-time exposed workers (OSHA 2006). However, Seidler et al. (2012) performed a risk assessment using published standardized mortality ratios (SMRs) for these cohorts calculated for grouped exposure data. These groups span across a wide range of individual Cr(VI) levels in particular for the respective lowest class: 0–28 lg/m 9 years in Park et al. (2004) and 0–60 lg/m 9 years in Gibb et al. (2000). This introduces an uncertainty about the precise exposure level associated with the lung cancer risk estimated for grouped exposure data. SMRs have various additional shortcomings, as the observed cases are compared with expected cases from an external reference population without adjusting for smoking. This might at least partially explain the increased lung cancer risk of 72 cases in the lowest exposure class of the Baltimore cohort that comprised many short-term exposed workers. The average exposure duration in the whole cohort was 5 months only. Seidler et al. (2012) performed a meta-analysis of the dose–response relation and depicted excess mortality risks in terms of additional cases per 1,000 workers for the male European population in Table 3 and 4. There is an apparent heterogeneity not only between the additional lung cancer cases per 1,000 workers in the individual studies but also This comment refers to the article available at doi: 10.1007/s00420-012-0822-0.