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, 45 nm for CeO2 and 7, 20 nm for TiO2). An increase in the expression of the cyp35a2 gene, decrease in fertility and survival parameters were observed in the 15 and 45 nm of CeO2 and in the 7 nm 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 (7 nm of TiO2 and 15 nm of CeO2) seemed to be more toxic than larger sized ones (20 nm of TiO2 and 45 nm 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.