Field evaluation of predictions of environmental effects from a multispecies-microcosm toxicity test

The predictive validity of a multispecies-microcosm toxicity test was evaluated. Predictions of biological response to a complex effluent were made from dose-response curves in laboratory tests and compared to observed effects in the receiving system. No effects on protozoan or macroinvertebrate communities were observed at the field site with effluent concentrations less than the chronic value of 1.7% effluent determined in laboratory tests. In addition, the microcosm test accurately predicted the magnitude of decreases in species richness in protozoan and macroinvetebrate communities in the receiving system at the first downstream site. Predictions of environmental effects for stations farther downstream were generally less accurate and too high, perhaps due to lack of persistence in the toxicity of the effluent. Stimulation of total biomass and algal growth were observed in both laboratory and field tests, but laboratory tests greatly overestimated the magnitude of enrichment responses in the receiving system.