Titanium dioxide nanoparticles enhance mortality of fish exposed to bacterial pathogens

Nano-TiO₂ is immunotoxic to fish and reduces the bactericidal function of fish neutrophils. Here, fathead minnows (Pimephales promelas) were exposed to low and high environmentally relevant concentration of nano-TiO₂ (2 ng g^-1 and 10 μg g^-1 body weight, respectively), and were challenged with common fish bacterial pathogens, Aeromonas hydrophila or Edwardsiella ictaluri. Pre-exposure to nano-TiO₂ significantly increased fish mortality during bacterial challenge. Nano-TiO₂ concentrated in the kidney and spleen. Phagocytosis assay demonstrated that nano-TiO₂ has the ability to diminish neutrophil phagocytosis of A. hydrophila. Fish injected with TiO₂ nanoparticles displayed significant histopathology when compared to control fish. The interplay between nanoparticle exposure, immune system, histopathology, and infectious disease pathogenesis in any animal model has not been described before. By modulating fish immune responses and interfering with resistance to bacterial pathogens, manufactured nano-TiO₂ has the potential to affect fish survival in a disease outbreak.