Toxicity of CeO₂ nanoparticles on a freshwater experimental trophic chain: A study in environmentally relevant conditions through the use of mesocosms

Abstract

The toxicity of CeO₂ NPs on an experimental freshwater ecosystem was studied in mesocosm, with a focus being placed on the higher trophic level, i.e. the carnivorous amphibian species Pleurodeles waltl. The system comprised species at three trophic levels: (i) bacteria, fungi and diatoms, (ii) Chironomus riparius larvae as primary consumers and (iii) Pleurodeles larvae as secondary consumers. NP contamination consisted of repeated additions of CeO₂ NPs over 4 weeks, to obtain a final concentration of 1 mg/L. NPs were found to settle and accumulate in the sediment. No effects were observed on litter decomposition or associated fungal biomass. Changes in bacterial communities were observed from the third week of NP contamination. Morphological changes in CeO₂ NPs were observed at the end of the experiment. No toxicity was recorded in chironomids, despite substantial NP accumulation (265.8 ± 14.1 mg Ce/kg). Mortality (35.3 ± 6.8%) and a mean Ce concentration of 13.5 ± 3.9 mg/kg were reported for Pleurodeles. Parallel experiments were performed on Pleurodeles to determine toxicity pathways: no toxicity was observed by direct or dietary exposures, although Ce concentrations almost reached 100 mg/kg. In view of these results, various toxicity mechanisms are proposed and discussed. The toxicity observed on Pleurodeles in mesocosm may be indirect, due to microorganism’s interaction with CeO₂ NPs, or NP dissolution could have occurred in mesocosm due to the structural complexity of the biological environment, resulting in toxicity to Pleurodeles. This study strongly supports the importance of ecotoxicological assessment of NPs under environmentally relevant conditions, using complex biological systems.

• Amphibian
• chironomidae
• ecotoxicity
• litter decomposition
• microorganisms

Acknowledgements

Thanks to Umicore company for providing CeO₂ NPs. The authors also thank Sophie Caissaignon and Corinne Chaneac (Collège de France, Paris, France) for CeO₂ NP characterization and Sylvain Lamothe for his helpful technical assistance. The authors also thank the CNRS for funding the GDRi iCEINT. The English language of the manuscript has been corrected by an English language editing company.

Declaration of interest

This study was conducted in the frame of the ANR-10-NANO-0006/MESONNET project, funded by the French National Research Agency (ANR). The authors report no conflict of interest. The authors alone are responsible for the content and writing of the paper.

Supplementary material available online

Supplementary Figures S1-S5