Poly(acrylic acid)-coated titanium dioxide nanoparticle and ultraviolet light co-exposure has minimal effect on developing zebrafish (Danio rerio)

Widespread production of titanium dioxide nanoparticles (TiO₂ NPs) for use in various consumer products has increased the potential for their release into the environment. Most studies examine TiO₂ NP toxicity under laboratory lighting that emits little to no ultraviolet (UV) radiation, yet these nanoscale particles are wide band-gap semiconductors capable of generating reactive oxygen species. The purpose of this study was to examine poly(acrylic acid)-coated TiO₂ NP phototoxicity in vivo. Zebrafish (Danio rerio) embryos were exposed to 0.1, 1 or 10 mg L^-1 of characterized uncoated TiO₂ NPs (positive control), polymer-coated TiO₂ NPs, and the polymer coating alone (negative control) in the presence or absence of UV light. Survival, hatching success, malformation, thiobarbituric acid reactive substances (TBARS), catalase activity, total glutathione (TG) level, superoxide dismutase activity, and alteration in antioxidant-related gene expression were measured. Uncoated TiO₂ NPs produced hydroxyl radicals (OH^•), delayed hatch, induced lipid peroxidation, increased catalase activity and TG levels, and upregulated glutathione peroxidase 1a gene expression 1.59 fold in the presence of UV light. Polymer-coated TiO₂ NP increased both TBARS production and TG levels under simulated sunlight illumination. We suggest that the polymer coating plays a role in OH^•-mediated effects of TiO₂ NPs in developing zebrafish and that toxicity depends on UV illumination. Since the presence of UV light evidently affects TiO₂ NP toxicity, the need for more environmentally representative nanotoxicity studies that take sunlight activation into account is strengthened.