Magnitude and mechanistic determinants of the interspecies toxicokinetic uncertainty factor for organic chemicals.

The interspecies uncertainty factor, UF(AH), of 10 was recently subdivided into two components to account separately for interspecies differences in toxicokinetics and toxicodynamics (UF(AH-TK)=3.16, UF(AH-TD)=3.16).

Probabilistic framework for the estimation of the adult and child toxicokinetic intraspecies uncertainty factors.

Human health risk assessments use point values to develop risk estimates and thus impart a deterministic character to risk, which, by definition, is a probability phenomenon. The risk estimates are calculated based on individuals and then, using uncertainty factors (UFs), are extrapolated to the population that is characterized by variability. Regulatory agencies have recommended the quantification of the impact of variability in risk assessments through the application of probabilistic methods.