This research examined the toxicity of complex industrial effluents as measured by chemical analyses, whole effluent toxicity (WET) tests and surveys of the receiving water biota. Toxicity of final effluents from 45 diverse facilities was examined to determine whether inferred toxicity based on presence and concentration of priority substances could predict WET, calculated from a battery of bioassays on bacteria, cladocerans and algae. Following corrections of inferred toxicity for particle-bound contaminants and adjustment for free ion activity, correlation between inferred and whole effluent toxicity was highly significant. Effluents with elevated metal concentrations exhibited lower WET than predicted, likely due to negative interactions among trace metals; kraft mill effluents exhibited higher WET than predicted which is consistent with findings in the literature. / The ability of laboratory WET tests to predict thresholds of invertebrate community response to a complex industrial effluent was examined. Patterns in invertebrate community structure were detrended for environmental factors and compared to measured instream effluent concentrations. Laboratory effect thresholds, reported as Maximum Allowable Toxicant Concentrations (MATC), were calculated from a battery of toxicity tests on bacteria, algae, cladocerans and fish. Declines in taxonomic richness corresponded to calculated lab thresholds, while changes in abundance of total taxa and sensitive taxa, (Ephemeroptera, Plecoptera, Trichoptera) occurred at lower concentrations than predicted from MATCs. The tendency for invertebrate abundance to decline at lower instream effluent concentrations than richness supports findings in the literature. Lack of correspondence between lab and field thresholds may be ameliorated by the addition of behavior endpoints, (e.g. avoidance) to toxicity tests.

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