TiO₂ nanoparticle exposure and illumination during zebrafish development: Mortality at parts per billion concentrations

Photoactivation of titanium dioxide nanoparticles (TiO₂NPs) can produce reactive oxygen species (ROS). Over time, this has the potential to produce cumulative cellular damage. To test this, we exposed zebrafish (Danio rerio) to two commercial TiO₂NP preparations at concentrations ranging from 0.01 to 10 000 ng/mL over a 23 day period spanning embryogenesis, larval development, and juvenile metamorphosis. Fish were illuminated with a lamp that mimics solar irradiation. TiO₂NP exposure produced significant mortality at 1 ng/mL. Toxicity included stunted growth, delayed metamorphosis, malformations, organ pathology, and DNA damage. TiO ₂NPs were found in the gills and gut and elsewhere. The two preparations differed in nominal particle diameter (12.1 ± 3.7 and 23.3 ± 9.8 nm) but produced aggregates in the 1 μm range. Both were taken up in a dose-dependent manner. Illuminated particles produced a time- and dose-dependent increase in 8-hydroxy-2′-deoxyguanosine DNA adducts consistent with cumulative ROS damage. Zebrafish take up TiO₂NPs from the aqueous environment even at low ng/mL concentrations, and these particles when illuminated in the violet-near UV range produce cumulative toxicity.