The Application of Default Distributions of Assessment Factors in Human Health Risk Assessment. T. G. Vermeire, M. N. Pieters, M. A. J. Rennan, and P. M. J. Bos; RIVM, and TNO Nutrition and Food Institute
In the standard procedure for deriving Human Limit Values the NOAEL is divided by a number of assessment factors. These factors account for uncertainty and variability in the extrapolation from animal experimental results to humans. If substance-specific assessment factors cannot be derived, fixed default values are applied. A framework was proposed earlier in which it is acknowledged that in human risk assessment both the effect parameter and the assessment factors are uncertain and can best be described by lognormal distributions. The further operationalisation of this concept will be presented with regard to the use of default distributions of assessment factors. Default distributions are proposed for the interspecies and intraspecies assessment factors as well as for the factors used in the extrapolation from an experimental study of short duration to a study of longer duration. The probabilistic combination of the individual default distributions will be applied in the interpretation of the margin between the NOAEL and the expected human exposure (Margin Of Safety) and in the interpretation of the overall assessment factor as derived according to currently accepted methods. Examples are presented.
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