Coating with polysaccharides influences the surface charge of cerium oxide nanoparticles and their effects to Mytilus galloprovincialis

This study focused on the effects of surface coating, acquired through the interaction with natural biomolecules, on the behavior and ecotoxicity of nanoparticles (NPs). To this aim, the effects of Cerium Oxide Nanoparticles (CeO2NPs) naked and coated with chitosan and alginate on the marine mussel Mytilus galloprovincialis were compared. Mussels were exposed for 7 days to 100 μg L−1 of CeO2NPs and for 28 days to 1 μg L−1 of CeO2NPs. In both experiments CeO2NPs were used naked and coated with the two polysaccharides. The lowest tested concentration allowed to understand the environmental relevance of this biological process. A set of biomarkers related to oxidative stress/damage and energy metabolism was applied to assess the ecotoxicity of CeO2NPs. The aggregation and stability in water of CeO2NPs were measured through dynamic light scattering analysis and the levels of Ce in the exposure media and in mussels soft tissues were determined by inductively coupled plasma-mass spectrometry. Results showed a different hydrodynamic behavior and stability of CeO2NPs in saltwater related to the different coatings. Despite this, no differences in the bioaccumulation of CeO2NPs were observed among the experimental groups. Different coatings affected also CeO2NPs toxicological outcomes in both 7- and 28-days exposures. Coating with chitosan enhanced antioxidant enzyme activities while coating with alginate triggered oxidative damage. Although the oxidant pathways did not differ that much among the exposures, biomarkers of energetic supplies suggested a different strategy of defense in response to CeO2NP exposure at a lower concentration and for a longer period of time. The obtained results are in line with findings of a previous study on freshwater mussels, suggesting that the coating with biomolecules, which impart negative charge to the NPs, might enhance their biological effects. This study highlighted that interactions of NPs with natural biomolecules largely present in the aquatic environment could affect NPs toxicity altering the interaction towards organisms.