Different approaches for calculating the Mixture Assessment Factor (MAF)

The Mixture Assessment (or Allocation) Factor (MAF) is a pragmatic instrument to take into account the risks of a mixture already in the risk and safety assessment of the individual chemicals within the framework of the prospective risk assessment. Based on existing monitoring data for surface waters and published ecotoxicological data as well as predicted no-effect concentrations (PNEC) or environmental quality standards (EQS), different approaches to calculate the MAF are compared with regard to (1) the assumptions made, (2) the data required for the calculation, (3) the possibility to calculate percentiles of the MAF distributions, (4) the resulting MAF values and (5) the interdependence of the different approaches. The results will be communicated with two audiences in mind: the scientific community, to enable peer review of the results, and regulators and policy makers, to maximise the likelihood that the results can be used in regulatory processes.