Comparative Toxicity of TiO₂ and Sn-Doped TiO₂ Nanoparticles in Zebrafish After Acute and Chronic Exposure

This study was conducted to assess the toxicological potential of synthesized pure and Sn-doped TiO₂ NPs (Sn-TiO₂ NPs) in zebrafish after acute and chronic exposure. The pure TiO₂ NPs, 4%, and 8% Sn-TiO₂ NPs were synthesized and characterized using X-ray diffraction, Scanning Electron Microscope, diffuse reflectance spectra, dynamic light scattering, and zeta potential analyses. The pure TiO₂ NPs, 4%, and 8% Sn-TiO₂ NPs were spherical with average sizes of about 40, 28, and 21 nm, respectively, indicating significant size reduction of TiO₂ NPs following Sn doping. According to our results, the LC_50-96h increased in the order of 8% Sn-TiO₂ NPs (45 mg L^-1) < 4% Sn-TiO₂ NPs (80.14 mg L^-1) < pure TiO₂ NPs (105.47 mg L^-1), respectively. Exposure of fish to Sn-TiO₂ NPs after 30 days resulted in more severe histopathological alterations in gills, liver, intestine, and kidneys than pure TiO₂ NPs. Furthermore, Sn-doping significantly elevated malondialdehyde levels and micronuclei frequency, indicating increased oxidative stress and genotoxicity. Expression analysis revealed altered expression of various genes, including upregulation of pro-apoptotic Bax gene and downregulation of anti-apoptotic Bcl-2 gene, suggesting potential induction of apoptosis in response to Sn-doped NPs. Additionally, antioxidant genes (Gpx, Sod, Cat, and Ucp-2) and stress response gene (Hsp70) showed altered expression, suggesting complex cellular responses to mitigate the toxic effects. Overall, this study highlights the concerning impact of Sn-doping on the toxicity of TiO₂ NPs in zebrafish and emphasizes the need for further research to elucidate the exact mechanisms underlying this enhanced toxicity.