The presence of per-and poly-fluoroalkyl substances (PFAS) in environment poses a serious risks to organisms due to their persistence, bioaccumulation and negative effects. Among PFAS, perfluorooctanoate (PFOA) has been recognized as one of the most hazardous compounds. Despite extensive research on PFOA toxicity, its effects on ecosystem structure and functioning remain poorly understood, as most studies focused on classical model organisms providing limited information on ecosystem-level responses. The aim of this study is to investigate the potential ecosystem-level toxicity induced by PFOA, using microcosms which contain a simplified freshwater ecosystem. The microcosm-experiment was conducted at Wageningen University. Microcosms containing a 3cm sediment layer, 12L of natural pond water, phytoplankton and zooplankton communities, macroinvertebrates (Asellus aquaticus, Gammarus pulex and Physella acuta) and a macrophyte (Myriophyllum spicatum), which were exposed for seven weeks to four PFOA-concentrations (1000μg/L; 100μg/L; 10μg/L; 1μg/L). Each treatment was replicated four times and the control six times. Ecosystem processes were evaluated weekly through measurements of dissolved oxygen fluctuations and physicochemical water parameters, while PFOA concentrations in the water were monitored at selected time point. The focal endpoints evaluated were connected to ecosystem structure and functioning: 1) measurements of phytoplankton biomass (chlorophyll-a); 2) organic matter decomposition; 3) zooplankton community composition; 4) macroinvertebrate abundance and feeding activity; 5) macrophyte growth and biomass. At the end of the experiment oxidative stress biomarkers were used to assess potential negative effects at sub-individual level on macrocrustaceans. Our preliminary results showed no significant effects of PFOA on ecosystem functioning parameters, although the results of some endpoints are not available yet. However, based on previous findings on oxidative stress biomarkers, we expect PFOA exposure to alter the oxidative status of the investigated macroinvertebrates. Overall, these results highlight the value of ecosystem-level approaches for assessing the effects and ecological risks of PFAS in aquatic environments.