ABSTRACT
The purpose of this chapter is to describe the scientific basis for extrapolation of toxicity findings in laboratory animals to predict outcomes in human populations. Such
extrapolation is often said to comprise two components, one qualitative in nature, the second quantitative. Qualitative extrapolations generally concern the nature of the toxic response (are the specific toxicity endpoints observed in test animals also expected in similarly
of the dose at which human beings and test animals are expected to be at equal risk of toxicity. Although both types of extrapolation are important, scientific understanding of the basis for quantitative extrapolations across species is more limited than is the basis for qualitative extrapolations. At the same time, because results from animal toxicity studies have become such important determinants of regulatory and other public health protection activities and because the latter typically require the establishment of quantitative limits on human exposure, questions regarding quantitative extrapolations have come to be seen as ultimately of greater significance than those that are purely qualitative in character. Thus, as in many other areas in which science plays a significant role in the development of social policies, the questions that are of most importance tend to be those about which science has the least clear answers. It is therefore no surprise that there is so much public skepticism about the predictions of toxicologists and risk assessors.
