Cerium Oxide Nanoparticles are More Toxic than Equimolar Bulk Cerium Oxide in Caenorhabditis elegans
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Engineered cerium oxide nanoparticles (CeO2 NPs) are widely used in biomedical and engineering manufacturing industries. Previous research has shown the ability of CeO2 NPs to act as a redox catalyst, suggesting potential to both induce and alleviate oxidative stress in organisms. In this study, Caenorhabditis elegans and zebrafish (Danio rerio) were dosed with commercially available CeO2 NPs. Non-nano cerium oxide powder (CeO2) was used as a positive control for cerium toxicity. CeO2 NPs suspended in standard United States Environmental Protection Agency reconstituted moderately hard water, used to culture the C. elegans, quickly formed large polydisperse aggregates. Dosing solutions were renewed daily for 3 days. Exposure of wild-type nematodes resulted in dose-dependent growth inhibition detected for all 3 days (p < 0.0001). Non-nano CeO2 also caused significant growth inhibition (p < 0.0001), but the scale of inhibition was less at equivalent mass exposures compared with CeO2 NP exposure. Some metal and oxidative stress-sensitive mutant nematode strains showed mildly altered growth relative to the wild-type when dosed with 5 mg/L CeO2 NPs on days 2 and 3, thus providing weak evidence for a role for oxidative stress or metal sensitivity in CeO2 NP toxicity. Zebrafish microinjected with CeO2 NPs or CeO2 did not exhibit increased gross developmental defects compared with controls. Hyperspectral imaging showed that CeO2 NPs were ingested but not detectable inside the cells of C. elegans. Growth inhibition observed in C. elegans may be explained at least in part by a non-specific inhibition of feeding caused by CeO2 NPs aggregating around bacterial food and/or inside the gut tract.
KeywordsCerium CeO2 Paraquat United States Environmental Protection Agency Zebrafish Embryo
This work was supported by the National Science Foundation (NSF) and the USEPA under NSF Cooperative Agreement No. EF-0830093, Center for the Environmental Implications of NanoTechnology. Any opinions, findings, conclusions, or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the NSF or the USEPA. This work has not been subjected to USEPA review, and no official endorsement should be inferred. All strains except JF23 were originally provided by the C. elegans Reverse Genetics Core Facility at the University of British Colombia, which is part of the International C. elegans Gene Knockout Consortium and is supported by the National Institute of Health—Office of Research Infrastructure Programs (Grant No. P40 OD010440). We gratefully acknowledge Elena Turner, Xinyu Yang, and Axel Berky for experimental assistance.
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