Use of Uncertainty Factors by the SCOEL in their derivation of health-based Occupational Exposure Limits

Abstract

The aim of this study was to investigate how the Scientific Committee on Occupational Exposure Limits (SCOEL) of the European Commission uses uncertainty factors when proposing health-based indicative occupational exposure limit values (IOELVs). In total, 75 IOELVs in 62 summary documents published from 1991 to 2003 were analyzed. For 31 of the IOELVs, no explicit uncertainty factor (EUF) was stated. For these, we calculated an implicit safety margin (ISM) as the ratio between the point of departure (POD, derived from the NOAEL or LOAEL of the critical effect) and the proposed IOELV. We further analysed whether date of recommendation, type of critical effect, nature of POD or amount of available data influenced the magnitude of the EUFs and ISMs. The ISMs varied little (range 1-5), while the EUFs showed more variability (range 1-50). The EUFs remained unaffected over time and the ISMs decreased slightly. Significant differences in the magnitude of the EUFs, but not ISMs, were found between critical effects, however, contrary to expected the average EUFs and ISMs for irritation were similar to those for more severe systemic effects. The nature of the POD affected the ISMs and EUFs only slightly and less than expected. Both EUFs and ISMs showed a weak but significant negative correlation with the amount of available toxicological data, measured as the number of relevant publications in PubMed, whereas SCOEL statements on data sufficiency had no influence. Overall, the most striking difference was that between EUFs and ISMs, the former being on average 2.1 times higher.

Key words::

• Assessment factor
• regulatory toxicology
• risk assessment
• risk management
• safety factor

Acknowledgements

We are grateful to Professors Christina Rudén and Sven Ove Hansson for valuable comments during the elaboration of this manuscript.

Declaration of interest

The work has been partly performed as part of an ongoing project financed by the Swedish Work Environment Authority with the aim to elucidate the methodologies to derive OELs and DNELs. The authors′ affiliations are as shown on the cover page. Gunnar Johanson is a member of the SCOEL. The authors have sole responsibility for the content and writing of the paper.