Current laboratory tests examine only the responses of individuals, which are then averaged to give a mean response for the test species. With given constraints of limited finances and number of personnel, it is not possible to identify the most sensitive species or group of species. . . . The data are too limited in scope for extrapolations to be made from them to responses of other (even closely related) species. (pp. xi-xii)
After more than 15 years, we still do not know whether effluent bioassays sufficiently protect species in the field from direct toxic effects, and we do not have well-established methods for extrapolating from single-species toxicity measurements to community- and ecosystem-level effects of effluents. Although this is perhaps not surprising given the complexity of ecosystems and the number of variables involved, it must be recognized that this limitation in our understanding severely limits our ability to reliably extrapolate from the results of single-species bioassays to effects on receiving ecosystems.
It is important to define the proper role of single-species bioassays. Single-species bioassays are suitable for developing water-quality criteria for particular chemicals, based on the assumption that these criteria protect individuals and that no synergistic effects occur with other chemicals in the environment. They are also useful as an initial screen to detect effluent toxicity. However, bioassays alone cannot ensure that effluents will not harm the ecosystems into which they are released.
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