Toxicity investigation of CeO 2 nanoparticles coated with glucose and exopolysaccharides levan and pullulan on the bacterium Vibrio fischeri and aquatic organisms Daphnia magna and Danio rerio.

Cerium oxide nanoparticles (nCeO ₂ ) have widespread applications, but they can be hazardous to the environment. Some reports indicate the toxic effect of nCeO ₂ on tested animals, but literature data are mainly contradictory. Coating of nCeO ₂ 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 nCeO ₂ . 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 nCeO ₂ in comparison to uncoated nCeO ₂ using different model organisms. The aim of this study was to test the acute toxicity of carbohydrate-coated nCeO ₂ 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 nCeO ₂ 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 nCeO ₂ on Vibrio fischeri. The coating of nCeO ₂ did not affect the nanoparticles' accumulation/adsorption or mortality in Daphnia magna or Danio rerio. Monitoring of respiration in Daphnia magna revealed changes in CO ₂ production after exposure to coated nCeO ₂ , while the crustacean's O ₂ consumption was not affected by any of the coated nCeO ₂ . In summary, this study revealed that, at 200 mg L ^-1 , uncoated and carbohydrate-coated nCeO ₂ are not toxic for the tested organisms, however, the CO ₂ production in Daphnia magna is different when they are treated with coated and uncoated nCeO ₂ . The highest production was in glucose and levan-coated nCeO ₂ according to their highest suspension stability. Daphnia magna (D. magna), Danio rerio (D. rerio), Vibrio fischeri (V. fischeri).
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