International audience Cerium nanoparticles (nCeO(2)) are widely used in everyday products, as fuel and paint additives. Meanwhile, very few studies on nCeO(2) sublethal effects on aquatic organisms are available. We tried to fill this knowledge gap by investigating short-term effects of nCeO(2) at environmentally realistic concentrations on two freshwater invertebrates; the amphipod Gammarus roeseli and the bivalve Dreissena polymorpha, using an integrated multibiomarker approach to detect early adverse effects of nCeO(2) on organism biology. Differences in the behaviour of the organisms and of nanoparticles in the water column led to differential nCeO(2) bioaccumulations, G. roeseli accumulating more cerium than D. polymorpha. Exposure to nCeO(2) led to decreases in the size of the lysosomal system, catalase activity and lipoperoxidation in mussel digestive glands that could result from nCeO(2) antioxidant properties, but also negatively impacted haemolymph ion concentrations. At the same time, no strong adverse effects of nCeO(2) could be observed on G. roeseli. Further experiments will be necessary to confirm the absence of severe nCeO(2) adverse effects in long-term environmentally realistic conditions.