Exposure to Cerium Dioxide Nanoparticles Differently Affect Swimming Performance and Survival in Two Daphnid Species

The CeO(2) NPs are increasingly used in industry but the environmental release of these NPs and their subsequent behavior and biological effects are currently unclear. This study evaluates for the first time the effects of CeO(2) NPs on the survival and the swimming performance of two cladoceran species, Daphnia similis and Daphnia pulex after 1, 10 and 100 mg.L(−1) CeO(2) exposures for 48 h. Acute toxicity bioassays were performed to determine EC(50) of exposed daphnids. Video-recorded swimming behavior of both daphnids was used to measure swimming speeds after various exposures to aggregated CeO(2) NPs. The acute ecotoxicity showed that D. similis is 350 times more sensitive to CeO(2) NPs than D. pulex, showing 48-h EC(50) of 0.26 mg.L(−1) and 91.79 mg.L(−1), respectively. Both species interacted with CeO(2) NPs (adsorption), but much more strongly in the case of D. similis. Swimming velocities (SV) were differently and significantly affected by CeO(2) NPs for both species. A 48-h exposure to 1 mg.L(−1) induced a decrease of 30% and 40% of the SV in D. pulex and D. similis, respectively. However at higher concentrations, the SV of D. similis was more impacted (60% off for 10 mg.L(−1) and 100 mg.L(−1)) than the one of D. pulex. These interspecific toxic effects of CeO(2) NPs are explained by morphological variations such as the presence of reliefs on the cuticle and a longer distal spine in D. similis acting as traps for the CeO(2) aggregates. In addition, D. similis has a mean SV double that of D. pulex and thus initially collides with twice more NPs aggregates. The ecotoxicological consequences on the behavior and physiology of a CeO(2) NPs exposure in daphnids are discussed.