There is presently, a substantial amount of information being gathered concerning the environmental risk associated with the perfluorooctanoic acid (PFOA) compound. The aim of this paper was to determine a 35 day community no observable effect concentration (NOEC(community)) or lowest observable effect concentration (LOEC) for freshwater zooplankton exposed to PFOA during a study in 30 l indoor aquatic microcosms. Some significant (P < 0.01) temporal fluctuations in zooplankton abundance were observed, however, a NOEC(community) could not be calculated. LOEC for various species varied between 10 and 70 mg l(-1). According to LOEC values, the tentative order of descriptors sensitivity was as follows: Daphnia magna > richness > or = Cyclops canthocamptus staphylinus > Cyclops diaptomus>total zooplankton > or = Rotifera sp. The long term ecological significance of these temporal fluctuations could not be determined in this study, however, the overall study cessation analysis showed that the structure of the ecosystem was changed from a more diverse community dominated by larger species towards a less diverse community dominated by smaller more and robust species (P < 0.05). Additional chronic toxicity testing should also be addressed since these compounds are so persistent and recalcitrant.