Use of microcosm and fish toxicity data to select mesocosm treatment concentrations.

Data from Mixed Flask Culture (MFC) microcosms and fish single species toxicity tests were used to select treatment concentrations for littoral enclosure studies. Selected concentrations were evaluated by comparing the predicted responses to those observed in littoral enclosure studies with a pyrethroid pesticide, esfenvalerate (Lozano et al. 1989) and an organophosphate pesticide, azinphos-methyl (Knuth et al. 1992). Comparisons of the effects predicted by these laboratory studies and effects that occurred in the two littoral enclosure trials provided useful information on the accuracy associated with each prediction. Although the approach did not always predict the exact magnitude or breadth of response found in the littoral enclosures, response levels for each of the selected treatment concentrations were adequate to describe the dose-response relationship of the littoral ecosystem for the two pesticides. The evaluation suggests that selection of treatment concentrations for the two littoral enclosure studies could have been improved by using this approach.