Photodecomposition of bisphenol A on nanometer-sized TiO2 thin film and the associated biological toxicity to zebrafish (Danio rerio) during and after photocatalysis

We investigated the relationship between the TiO2 photocatalytic decomposition of bisphenol A and biological toxicity to zebrafish (Danio rerio). TiO2 particles, which prepared using a solvothermal method, were applied to produce a nanometer-sized TiO2 thin film. An alcoholic solution containing the TiO2 particles and an inorganic binder was directly coated on the UV-lamp substrate. It was equipped in a photoreactor that was manufactured in our laboratory. The attachment of the thin TiO2 film to the UV-lamp substrate resulted in a stable and transparent coating. The TiO2 particles on the thin film were approximately 20–30 nm in size, and the resulting film thickness was approximately 200 nm after a single coat. The bisphenol A, which was eluted from epoxy resin in a drinking water tank, was completely degraded by the TiO2 photocatalysis. We initially detected approximately 7.8 ng/ml of bisphenol A in the epoxy-resin tank, but its concentration was undetectable after a 48-h photocatalytic reaction over TiO2. We observed a decreased survival rate in zebrafish that were reared in water exposed to the leaching process of the epoxy resin. After the photocatalysis, however, no toxic effects on the hatching rates or morphogenesis of the zebrafish were observed. In summary, toxicity during the TiO2 photocatalysis was observed; however, toxicity was no longer observed once the bisphenol A was completely decomposed by the TiO2 photocatalysis. On the basis of these experimental observations, we suggest that TiO2 photocatalysis can be adopted as a treatment method to purify an epoxy-resin tank.