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Aquatic multispecies tests are an extremely flexible and powerful tool in aquatic ecology, especially in the study of the fates and effects of xenobiotics, but are not amenable to the type of protocol development and precision required to be part of a formal hazard assessment scheme. Such methods are completely antithetical to the most efficient use of multispecies tests, which is the ability to design a system to elucidate particular mechanisms and interactions in specific ecosystems. One goal of hazard assessment schemes is to remove the subjectivity of individual researchers from the process. Multispecies tests will not achieve this goal. Instead, aquatic multispecies tests of all sizes and configurations should be used by researchers to answer questions posed about the behavior and effects of xenobiotics in aquatic environments. Therefore, rather than designing experiments to test whether multispecies toxicity tests are accurate or replicable they should be used to elucidate mechanisms and make tests of relevant hypotheses within the overall framework of aquatic ecotoxicology. Because of the diversity of interactions among organisms and xenobiotics and the environments on which they exist, one will never be able to absolutely establish the accuracy of multispecies tests. Simply because multispecies tests are more complex does not mean that they are more realistic or have more predictive power than single-species tests. In fact, they may be more prone to artifacts. There is no evidence to suggest that multispecies toxicity tests, as a class, are more sensitive than the more traditional method of establishing criteria from final chronic values, based on single-species tests. More research on multispecies replicability is not necessary. Replicability is a statistical problem rather than an intrinsic property, and appropriate tests and designs are available to determine the relative variability, and therefore the sensitivity of laboratory-scale multispecies test, and they allow the appropriate number of stratified replications to be determined to make the test sufficiently replicable to make precise conclusions. Multispecies tests may be more efficient than conducting several single-species tests because of a greater range of sensitivities of test organisms, however, this has not been established. The most useful types of multispecies toxicity tests will be in-situ-type systems where some replication can be accomplished in a more realistic system or multispecies tests of mesocosm-scale. Further research is needed in the area of validation studies of in-situ systems.
aquatic biology, communities, tests, microcosms, impact assessment, ecosystem
Professor and coordinator of environmental effects research, Center for Environmental Toxicology, Michigan State University, East Lansing, MI