Toxicity of Titanium Dioxide-Cerium Oxide Nanocomposites to Zebrafish Embryos: A Preliminary Evaluation

The widespread use of metal nanoparticles in different fields has raised many doubts regarding their possible toxicity to living organisms and the accumulation and discharge of metals in fish species. Among these nanoparticles, titanium dioxide (TiO₂) and cerium oxide (CeO₂) nanoparticles have mainly been employed in photocatalysis and water depuration. The aim of this research was to evaluate the potential toxic effects, after a co-exposure of TiO₂-3%CeO₂ nanoparticles, on zebrafish development, using an acute toxicity test. Increasing concentrations of TiO₂-3%CeO₂ nanoparticles were used (0.1-1-10-20 mg/L). The heartbeat rate was assessed using Danioscope^TM software (version 1.2) (Noldus, Leesburg, VA, USA), and the responses to two biomarkers of exposure (Heat shock proteins-70 and Metallothioneins) were evaluated through immunofluorescence. Our results showed that the co-exposure to TiO₂-3%CeO₂ nanoparticles did not affect the embryos' development compared to the control group; a significant difference (p < 0.05) at 48 hpf heartbeat for the 1, 10, and 20 mg/L groups was found compared to the unexposed group. A statistically significant response (p < 0.05) to Heat shock proteins-70 (Hsp70) was shown for the 0.1 and 1 mg/L groups, while no positivity was observed in all the exposed groups for Metallothioneins (MTs). These results suggest that TiO₂-3%CeO₂ nanocomposites do not induce developmental toxicity; instead, when considered separately, TiO₂ and CeO₂ NPs are harmful to zebrafish embryos, as previously shown.