Alginate coating modifies the biological effects of cerium oxide nanoparticles to the freshwater bivalve Dreissena polymorpha

Highlights: • Coatings with alginate or chitosan modified hydrodynamic behaviour of CeO2NPs • The different coatings did not affect Ce accumulation in zebra mussels. • Ce@Alginate NPs increased the level of several free amino acid in zebra mussels. • Ce@Alginate NPs seem to affect mussel energetic metabolism and osmoregulation. The adsorption of biomacromolecules is a fundamental process that can alter the behaviour and adverse effects of nanoparticles (NPs) in natural systems. While the interaction of NPs with natural molecules present in the environment has been described, their biological impacts are largely unknown. Therefore, this study aims to provide a first evidence of the influence of biomolecules sorption on the toxicity of cerium oxide nanoparticles (CeO₂NPs) towards the freshwater bivalve Dreissena polymorpha. To this aim, we compared naked CeO₂NPs and coated with alginate and chitosan, two polysaccharides abundant in aquatic environments. Mussels were exposed to the three CeO₂NPs (naked, chitosan- and alginate-coated) up to 14 days at 100 μg L⁻¹, which is a concentration higher than the environmental one predicted for this type of NP. A suite of biomarkers related to oxidative stress and energy metabolism was applied, and metabolomics was also carried out to identify metabolic pathways potentially targeted by CeO₂NPs. Results showed that the coating with chitosan reduced NP aggregation and increased the stability in water. Nonetheless, the Ce accumulation in mussels was similar in all treatments. As for biological effects, all three types of CeO₂NPs reduced significantly the level of reactive oxygen species and the activity of superoxide dismutase, glutathione peroxidase and glutathione-S-transferase. The effect was more pronounced in individuals exposed to CeO₂NPs coated with alginate, which also significantly induced the activity of the electron transport system. Metabolomics analysis of amino acid metabolism showed modulation only in mussels treated with CeO₂NPs coated with alginate. In this group, 25 metabolites belonging to nucleotides, lipids/sterols and organic osmolytes were also modulated, suggesting that the nanoparticles affect energetic metabolism and osmoregulation of mussels. This study highlights the key role of the interaction between nanoparticles and natural molecules as a driver of nanoparticle ecotoxicity.