The cerium oxide nanoparticles toxicity induced physiological, histological and biochemical alterations in freshwater mussels, Unio crassus

Abstract

**Introduction:** Releasing of cerium oxide nanoparticles (nano-CeO₂) to the nature has increased due to the widespread use in many fields ranging from cosmetics to the food industry. Therefore, nano-CeO₂ has been included in the Organization for Economic Co-operation and Development's (OECD) priority list for engineering nanomaterials. In this study, the effects of nano-CeO₂ on the freshwater mussels were investigated to reveal the impact on the freshwater systems on model organism.

**Methods:** First, the chemical and structural properties of nano-CeO₂ were characterized in details. Second, the freshwater mussels were exposed to environmentally relevant concentrations of nano-CeO₂ as 10 mg, 25 mg and 50 mg/L during 48-h and 7-d. Third, after the exposure periods, hemolymph and tissue samples were taken to analyse the Total Hemocyte Counts (THCs) histology and oxidative stress parameters (total antioxidant status, glutathione, glutathione-S-transferase, and advanced oxidative protein products).

**Results:** Significant decrease of the THCs was observed in the nano-CeO₂ exposed mussels compared to the control group (P < 0.05). The histological results showed a positive association between nano-CeO₂ exposure concentration in the water and level of tissue damage and histopathological alterations were detected in the gill and the digestive gland tissues. Oxidative stress parameters were slightly affected after exposure to nano-CeO₂ (P > 0.05). In conclusion, this study showed that acute exposure of freshwater mussels to nano-CeO₂ did not pose significant biological risk. However, it has been proven that mussels are able to accumulate nano-CeO₂ significantly in their bodies.

**Conclusion:** This suggests that nano-CeO₂ may be a potential risk to other organisms in the ecosystem through trophic transfer in the food-web based on their habitat and niche in the ecosystem.