Acute Toxicity of Colloidal Silicon Dioxide Nanoparticles on Amphibian Larvae: Emerging Environmental Concern

Emerging contaminants derive from pharmaceuticals, pesticides, disinfection by-products, home and care products, and wood preservation and industrial chemicals that contain specific drugs, metals, metal oxides and metalloids as nanoparticles (NPs) in their formulations. Although the use of silicon dioxide (SiO2) NPs in commercial products increases, its impacts on the environment and on animal and human health are largely unknown. Thus, the aim of this study was to evaluate the ecotoxicity of colloidal SiO2-NPs in Rhinella arenarum larvae exposed to 0.001, 0.01, 0.1, and 1 mg/L colloidal SiO2-NPs for 48 h. Biotoxicological endpoints (median lethal concentration-LC50 ; 95% confidence limits), the no-observed-effect concentration (NOEC), the lowest-observed-effect concentration (LOEC), Toxic Units (TU), oxidative stress enzyme activity (glutathione S-transferase-GST), and genotoxicity (frequency of micronuclei, and other erythrocyte nuclear abnormalities-ENAs) were measured in exposed larvae. Scanning electron microscopy equipped with an energy dispersive X-ray system allowed detecting that SiO2-NPs aggregate on the dorsal skin of SiO2-treated larvae. The 48 h LC50 of colloidal SiO2-NPs was 0.0251 mg/L (0.0163- 0.0338 mg/L). The NOEC and LOEC values after 48 h were 0.001 mg/L and 0.01 mg/L, respectively. According to the hazard classification system for wastewaters discharged into the aquatic environment, the colloidal SiO2-NPs evaluated are Class V, i.e., of very high acute toxicity (TU = 3984.06). At 48 h of exposure to NOEC, GST activity and ENAs frequency were significantly increased (118.75 and 58%, respectively) with respect to controls. The results of the present study indicate that, at low concentration, colloidal SiO2-NPs exerted high toxicity on R. arenarum tadpoles.