Effects of realistic concentrations of TiO₂ and ZnO nanoparticles in Prochilodus lineatus juvenile fish

Abstract

The impact of nanoparticles on fish health is still a matter of debate, since nanotechnology is quite recent. In this study, freshwater benthonic juvenile fish Prochilodus lineatus were exposed through water to three concentrations of TiO₂ (0.1, 1, and 10 μg l⁻¹) and ZnO (7, 70, and 700 μg l⁻¹) nanoparticles, as well as to a mixture of both (TiO₂ 1 μg l⁻¹ + ZnO 70 μg l⁻¹) for 5 and 30 days. Nanoparticle characterization revealed an increase of aggregate size in the function of concentration, but suspensions were generally stable. Fish mortality was high at subchronic exposure to 70 and 700 μg l⁻¹ of ZnO. Nanoparticle exposure led to decreased acetylcholinesterase activity either in the muscle or in the brain, depending on particle composition (muscle—TiO₂ 10 μg l⁻¹; brain—ZnO 7 and 700 μg l⁻¹), and protein oxidative damage increased in the brain (ZnO 70 μg l⁻¹) and gills (ZnO 70 μg l⁻¹ and mixture) but not in the liver. Exposed fish had more frequent alterations in the liver (necrosis, vascular congestion, leukocyte infiltration, and basophilic foci) and gills (hyperplasia and epithelial damages, e.g., epithelial disorganization and epithelial loss) than the control fish. Thus, predicted concentrations of TiO₂ and ZnO nanoparticles caused detectable effects on P. lineatus that may have important consequences to fish health. But, these effects are much more subtle than those usually reported in the scientific literature for high concentrations or doses of metal nanoparticles.