Investigation of number, amount and structural properties of engineering nanoparticles in terms of aquatic ecotoxicology

The release of Cerium oxide nanoparticles (nano-CeO2) to the environment has increased with extensive usage of them in many areas ranging from cosmetics to food industry. Therefore, it is included in the Organization for Economic Co‐operation and Development (OECD) priority list of engineered nanomaterials. The present study was carried out to assess the nano-CeO2 toxicity on the freshwater midge, Chironomus riparius larvae at concentrations of 2.5, 25, 250, 2500 mg of CeO2 NP/kg of sediment and freshwater mussels, Unio crassus, at concentrations of 10 mg, 25 mg, and 50 mg of CeO2 NP/L in freshwater. Firstly, the chemical and structural properties of nano-CeO2 were characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), X‐ray photoelectron spectroscopy (XPS), A Brunauer–Emmett–Teller (BET), dynamic light scattering (DLS) and zeta potential analyses. The prolonged exposure of midges to nano-CeO2 were designed according to OECD test guide 218. The following parameters were investigated: nano-CeO2 uptake by the larvae, oxidative stress parameters, in vivo genotoxic effect and life trait parameters (developmental time, emergence, mortality and survival rate). ICP-MS analysis showed significant positive correlation between the concentration of the nano-CeO2 in the sediment and its uptake by the larvae. No significant mortality was observed in Chironomus riparius and oxidative stress was not detected. Nevertheless, significant DNA damage was detected in the midges at concentrations of 25 mg/kg and higher, in a dose-dependent manner. Obtained results indicate that nano-CeO2 is not directly toxic to chironomids. Furthermore, the only significantly induced sublethal effect is genotoxicity which begin to manifest at a concentration of 25 mg/kg of sediment and is progressively increasing at higher concentrations. Two types of time intervals (48 hours and 7 days) were designed to investigate the effect of nano-CeO2 exposure on mussels. The following parameters were investigated: nano-CeO2 uptake by mussels, calculation of total hemocyte counts, histopathology and biochemical analysis (biomarker experiments). Although no significant mortality was observed during the experiments' time frame, histopathology results showed a positive correlation between the concentration of CeO2-NPs in the water and the amount of tissue damage. Furthermore, no significant alteration was detected in biomarker analysis. However, it was observed in binary comparisons that oxidation stress parameters were deviating. As a result, our experiment indicates that exposure to nano-CeO2 does not induce biological risk for freshwater midges and mussels during acute exposure. In addition, the location of midges and mussels in the ecosystem may pose a risk through trophic transfer to other organisms of the food web due to the significant accumulation and biomagnification of nano-CeO2 in the midges and mussels.