Use of uncertainty factors by the European Commission Scientific Committee on Occupational Exposure Limits: a follow-up.

Decision on the safety margin, for instance by using uncertainty factors (UFs), is a key aspect in setting Occupational Exposure Limits (OELs). We analyzed the UFs in 128 OEL recommendations from the European Commission's Scientific Committee on Occupational Exposure Limits (SCOEL). We investigated factors expected to potentially influence the UFs, as well as a selection of factors that might influence how expert groups perceive quality or reliability of key studies. We extracted UFs explicitly stated in the recommendations (EUFs) and, when EUFs were missing, calculated an implicit safety margin (ISM) by dividing the point of departure (PoD) by the OEL. EUFs and ISMs were lower for recommendations based on human data than those based on animal data. EUFs and ISMs were also lower for No-Observed Adverse Effect Concentrations (NOAECs) than Lowest Observed Adverse Effect Concentrations (LOAECs). We saw no differences based on local vs systemic critical effects. Acute data resulted in lower EUFs and ISMs than subchronic. We saw no influence from status of key study (publication status, performer or funder), but high tonnage substances (1,000,000+ tonnes) have lower EUFs and ISMs than substances currently not registered under REACH. Although SCOEL methodology stated that UF should be documented, only 65 out of 128 OEL recommendations included an EUF. Indeed, the ratio of EUFs to ISMs even decreased from 1991-2003 to 2004-2017. Additionally, EUFs were, on average, 1.8 times higher than ISMs. We conclude that a more articulate framework for using UFs could enhance consistency and transparency of the SCOEL recommendations.