211 How to use reverse dosimetry to derive acceptable occupational exposure level from internal values

Abstract New approach methodologies (NAMs) are an integral part of Next Generation Risk Assessment (NGRA). NAMs consider in-vitro, in-silico, in-chemistry test methods. These can be linked by PBK modelling and in-vitro in-vivo extrapolation (IVIVE) to external exposure concentrations. Thus NAM-based test methods require translation from external exposure to internal exposure and vice versa. Additionally aggregated external human exposure by inhalation and dermal route will be often based on measurements or are estimated by tools usually applied under REACH. PBK modelling allows to predict chemical and metabolite concentrations over time and in relevant body compartments (human plasma and/or tissues) for given exposure scenarios (forward dosimetry). By turning around the approach (reverse dosimetry) acceptable external exposure levels (such as OEL) may be derived on internal thresholds (in-vitro effect data, compound specific threshold values, human biomonitoring data). Thereby, maximal external exposure concentrations below which human exposure is considered safe can be derived. The presentation will contain the description of the approach to derive acceptable occupational exposure levels (OELs) based on internal threshold values. The approach will be discussed with a case study to illustrate the applicability. The approach is beneficial especially for case compounds such as NMP where aggregated exposure is determined by inhalation and dermal by air.