Influence of TiO2 nano-objects characteristics on Caernorhabditis elegans development

Metal oxide nanoparticles (NPs) such as titanium dioxide (TiO2) are in the center of attention, because of their outstanding properties and relatively low cost of production. However, synthesis and utilization of NPs potentially also involve release and accumulation in the environment. Few data are available concerning the potential toxicity of NPs on ecosystems. In this context, we study the ecotoxicological effects of both native and fluorescently-tagged TiO2 nano-objects with different morphologies (P25 Evonik, nanotubes, nanoneedles) on the nematode Caenorhabditis elegans population. This worm is commonly used in ecotoxicological assays because of its convenient handling in the laboratory, and its sensitivity to different stresses. NPs ingestion by L1 and L4 larvae was studied by fluorescence microscopy and ion beam analysis. NPs were found in the pharynx and in the intestine lumen whatever the larvae stage. The quantity of ingested and detected NPs was dependent of the presence of food during exposure in the medium. Without feeding, an increased NPs ingestion was found in association with a strong intestine anterior dilatation. This phenomenon was also generally observed following starvation and in a longer delay of experiment. The toxicity of TiO2 NPs in C. elegans was evaluated using three different endpoints: lethality, worm length and reproduction. Whatever the NPs and larvae stage, the resulting data obtained showed only mortality in L1 exposed with nanotubes. A significant decrease of worm length was observed for L1 and L4 exposed whatever the morphology of NPs as compared to untreated group. The reproduction of C. elegans was clearly affected with a decrease of the eggs number per worm. Our findings suggest that the NPs toxicity depends very much on their physico-chemical characteristics (size, morphology) and has a different impact on the larvae stage exposed.