Aquatic invertebrates should be included in toxicity tests to assess the hazards of toxicants because of their ecological and economic importance and their morphological, physiological, and ecological diversity. The practical advantages to the use of aquatic invertebrates in toxicity tests are the small size and short life cycles of most species, and the fact that it is possible to produce genetically uniform cultures of certain species and to standardize stocks of other species. Considerations in designing toxicity tests with aquatic invertebrates include the lack of culture methods for many species, the variation in sensitivity of aquatic invertebrates throughout the life cycle and with previous exposure to toxicants, and the difficulty in ascertaining death.

Most laboratory toxicity tests are measures of acute lethality obtained under controlled and constant conditions; the data are available for relatively few species and usually have been obtained using single species. Since such data do not reflect environmental conditions and the complexity of aquatic ecosystems, they are often of limited use in predicting effects of toxicants on aquatic ecosystems or on aquatic organisms valued by man. The utility of laboratory toxicity tests can be increased by the use of protocols that emphasize the most sensitive procedures, such as life-cycle studies or tests with model ecosystems, and such tests should include several aquatic invertebrates from different levels in the food chain, exhibiting different responses to toxicants, plus other aquatic organisms. Laboratory test conditions should reflect, as far as possible, the test organism's ecological requirements and should not constrain the test organism's natural behavior. Additional studies also are required to describe the effect of toxicants on natural aquatic ecosystems to ensure that toxicity tests do predict the actual effects of toxicants on aquatic ecosystems.