Simple laboratory aquatic ecosystem models composed of naturally coadapted communities of phytoplankton, bacteria, zooplankton, and small benthic invertebrates were developed and evaluated for their effectiveness and consistency in screening the ecological impacts of pesticides on community functions. These generic microcosm toxicity tests were used to rank the potential hazard of pesticides on community metabolic processes. The reproducibility of hazard rankings was evaluated in sequential experiments with the same microcosm inoculum, and in simultaneous experiments using two sets of microcosms with taxonomically different community inocula, but the same major functional groups present (i.e., primary producers, grazers, detritivores, and decomposers). Based on an integrated measure of system response, relative impact, which accounts for both the magnitude and duration of displacement of defined treatment effects from the normal range of control system functions, these generic test systems were remarkably consistent in ranking pesticide impacts on community metabolic activities.

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