Toxicity investigation of CeO2 nanoparticles coated with glucose and exopolysaccharides levan and pullulan on the bacterium Vibrio fischeri and aquatic organisms Daphnia magna and Danio rerio

Highlights: • Levan and pullulan coated CeO₂ nanoparticles decrease toxicity to V. fischeri. • Coating increased nanoparticles' bioaccumulation in Daphnia magna. • All coated CeO₂ decrease the toxicity of uncoated ones at 100 mg L⁻¹ in D. magna. • Glucose-coated CeO₂ increased the CO₂ production in Daphnia magna at 200 mg L⁻¹. • Uncoated and coated CeO₂ did not affect early zebrafish development and mortality. Cerium oxide nanoparticles (nCeO₂) have widespread applications, but they can be hazardous to the environment. Some reports indicate the toxic effect of nCeO₂ on tested animals, but literature data are mainly contradictory. Coating of nCeO₂ can improve their suspension stability and change their interaction with the environment, which can consequently decrease their toxic effects. Herein, the exopolysaccharides levan and pullulan, due to their high water solubility, biocompatibility, and ability to form film, were used to coat nCeO₂. Additionally, the monosaccharide glucose was used, since it is a common material for nanoparticle coating. This is the first study investigating the impact of carbohydrate-coated nCeO₂ in comparison to uncoated nCeO₂ using different model organisms. The aim of this study was to test the acute toxicity of carbohydrate-coated nCeO₂ on the bacterium Vibrio fischeri NRRL B-11177, the crustacean Daphnia magna, and zebrafish Danio rerio. The second aim was to investigate the effects of nCeO₂ on respiration in Daphnia magna which was performed for the first time. Finally, it was important to see the relation between Ce bioaccumulation in Daphnia magna and Danio rerio and other investigated parameters. Our results revealed that the coating decreased the toxicity of nCeO₂ on Vibrio fischeri. The coating of nCeO₂ did not affect the nanoparticles' accumulation/adsorption or mortality in Daphnia magna or Danio rerio. Monitoring of respiration in Daphnia magna revealed changes in CO₂ production after exposure to coated nCeO₂, while the crustacean's O₂ consumption was not affected by any of the coated nCeO₂. In summary, this study revealed that, at 200 mg L⁻¹, uncoated and carbohydrate-coated nCeO₂ are not toxic for the tested organisms, however, the CO₂ production in Daphnia magna is different when they are treated with coated and uncoated nCeO₂. The highest production was in glucose and levan-coated nCeO₂ according to their highest suspension stability. Daphnia magna (D. magna), Danio rerio (D. rerio), Vibrio fischeri (V. fischeri)