ABSTRACT
Extrapolation is commonly used in human health and ecotoxicological risk assessment, either in a formal process or, more commonly, through the use of uncertainty factors derived from empirical experience or observation. Extrapolation is used in predictive risk assessment procedures, such as the setting of criteria or guidelines, as well as retrospective risk assessments, where organisms have already been exposed to a stressor. Matrix extrapolations are critical in understanding the bioavailability and fate of toxic substances and are driven by interactions between the matrix and the toxicant. Levels of biological organization are important for extrapolation, because more extrapolation data are available for lower levels of organization. Extrapolation between levels of biological organization is predicated on the correct choice of parameters to measure. Because most of the routine toxicity testing of environmentally important substances is carried out using species from temperate regions, spatial extrapolation is an important process in extending risk assessments to tropical or polar regions.
