require strict adherence to EPA protocols and quality assurance and quality control procedures.
Bioassays are effective tools for testing the toxicity of particular chemicals dissolved in water. They can also aid efforts to identify specific toxic compounds (Toxicity Identification Evaluations) or remove toxins from effluents (Toxicity Reduction Evaluations) (Mount and Anderson-Carnahan, 1988, 1989a,b). However, two important problems limit the use of bioassays as tools for protecting ecosystems from toxic effluents. First, the approved protocols present technical problems in application. Second and most important, effluent bioassay results do not enable the prediction of the effluent's impacts on other organisms or on ecosystem processes. In other words, acceptable toxicity in a bioassay is no guarantee that an effluent will not adversely affect the receiving habitat.
The results of effluent bioassays are sensitive to multiple variables unrelated to the effluents themselves, including genetic variation in test organisms, chemical composition of the water source used to dilute the effluent, and foods used in experiments. Therefore, bioassay results may not be reproducible if these variables are not held constant. In such cases, EPA may not be able to confirm the results of tests performed by effluent generators or other laboratories. However, the EPA must be able to reproduce test results submitted by independent laboratories if they are to carry out their enforcement responsibilities. Consequently, EPA protocols specify the use of "artificial waters" (solutions that combine distilled water with various salts in an effort to mimic a pristine, natural, standardized water source), particular food sources (e.g., commercially available fish food), and even particular clones (genotypes) of the test species (Baird et al., 1989; Finney, 1952a). The detailed specification of testing protocols has forced many entities subject to EPA regulations to hire independent testing laboratories to perform their tests. The resulting costs have led to widespread dissatisfaction with effluent bioassay requirements.
The second and more important shortcoming of effluent bioassays is the plethora of assumptions required to extrapolate test results to effects on receiving ecosystems. Neither a theoretical basis nor comprehensive test data validate the assumption that effluents that pass bioassays will not adversely affect receiving ecosystems. Such effluents may still harm ecosystems for either of two reasons: Test organisms may be less sensitive than other species to toxins in effluents, or