Ecotoxicological investigation of CeO₂ and TiO₂ nanoparticles on the soil nematode Caenorhabditis elegans using gene expression, growth, fertility, and survival as endpoints

In this study, the potential harmful effect of cerium dioxide (CeO₂), and titanium dioxide (TiO₂) nanoparticles on the environment was investigated using Caenorhabditis elegans ecotoxicity tests. Multiple toxic endpoints, such as stress-response gene expression, growth, fertility, and survival, were analyzed in C. elegans, in response to the CeO₂ and TiO₂ exposure. To investigate relationship between sizes of nanoparticles and toxicity, C. elegans were exposed to nanoparticles to the different sizes of nanoparticles (15, 45nm for CeO₂ and 7, 20nm for TiO₂). An increase in the expression of the cyp35a2 gene, decrease in fertility and survival parameters were observed in the 15 and 45nm of CeO₂ and in the 7nm of TiO₂ nanoparticles exposed to C. elegans. Gene knock-down experiment using RNA interference (RNAi) suggested that physiological level disturbances may be related with the cyp35a2 gene expression. Smaller sized nanoparticles (7nm of TiO₂ and 15nm of CeO₂) seemed to be more toxic than larger sized ones (20nm of TiO₂ and 45nm of CeO₂) on the observed toxicity. The size-dependent effect in CeO₂ and TiO₂ nanoparticles-induced toxicity needs to be investigated under more detailed experimental settings with the various sizes of nanoparticles. Further studies on the mechanism by which CeO₂ and TiO₂ nanoparticles affect cyp35a2 gene expression, fertility, and survival are warranted to better understand the CeO₂ and TiO₂ nanoparticles-induced ecotoxicity in C. elegans, as are studies with the causal relationships between these parameters. Overall results suggest that CeO₂ and TiO₂ nanoparticles have a potential for provoking ecotoxicity on C. elegans and the data obtained from this study can comprise a contribution to knowledge of the ecotoxicology of nanoparticles in C. elegans, about which little data are available.