The key problem faced by ecotoxicological scientists is to recognize the damaging effects of chemical pollutants on natural biota. On many occasions (for example, after accidental chemical releases or at sites of continuous point source discharges) damage is clearly visible,1–3 but insidious, long-term pollutant effects are more difficult to identify. During the last 20–30 years, ecotoxicologists have been compelled to attempt to predict whether a range of new chemicals that might potentially enter the natural environment is likely to affect ecosystems adversely. If such predictions suggest that certain chemicals pose real threats, managers and legislators must then be provided with information concerning the concentrations that will not elicit effects in the hope of setting safe limits and preventing environmental degradation. Current strategies of environmental management rely on:

Assessment of the potential toxicity of chemicals based on their physicochemical properties and, in particular, similarity to known toxicants — This is the so-called structure-activity relationship approach (SAR and QSARs).4

Assessment of actual toxicity under controlled laboratory conditions, with a limited number and variety of test organisms — Toxicity tests principally determine lethal concentrations of the chemical following uptake (usually from water in aquatic animals or from food in terrestrial animals) and no observable effect concentrations (NOECs), although increasing efforts are being made to assess effects on life cycles, fecundity, growth, etc.5 as well as effects on several species exposed simultaneously (multispecies toxicity tests).6

Monitoring studies — There are evaluations in which concentrations of the chemical in water, substrate, and selected biota are determined to evaluate the extent of contamination and to assess bioaccumulation and biomagnification.7

Ecological assessments — These are evaluations in which various ecological parameters (for example, species diversity, the presence or absence of key indicator organisms, nutrient cycling rates, etc.) are used to evaluate the impact of pollutants on various ecosystems.8