• inhibition concentration estimation;
  • hormesis;
  • bioconcentration factors;
  • weight of evidence


Legal mandates exist for the protection of wildlife and human health from the impacts of toxins released into the environment. To accomplish this objective, numeric environmental quality criteria are set. Toxicity test data are often analyzed in the development of such criteria. Regression-based estimators are frequently employed to calculate the concentration associated with a specified decrement/inhibition in response relative to control conditions. Non-monotonic concentration response patterns, often characterized as ‘hormesis’, may lead to alternative definitions of baseline responses for inhibition concentration calculations. In particular, the presence of hormesis may suggest that the definition of an impact measure is not always clear. In other cases, the impact measure may be clearly defined; however, adequate statistical study of such measures may not have been conducted. The bioconcentration factor, an index of how a toxicant accumulates within an aquatic organism relative to water, is an example where point estimates are often reported; however, reports of precision or confidence intervals are rare. A second example is the use of a no-observed-effect concentration, the highest concentration with responses that do not statistically differ from responses in the control group. Finally, multiple lines of evidence (e.g. toxicological, ecological, chemical, etc.) might be available to evaluate the degree of contamination at a particular site. The combination of this information to obtain overall site contamination assessment is a continuing challenge. These three issues provide a framework for discussing impact in environmental toxicology. Copyright © 2003 John Wiley & Sons, Ltd.