Effects of light condition and particle size on toxicity of nano-TiO2 on Daphnia magna

Abstract

Background Titanium dioxide (TiO2) is known to have photocatalytic activity and ultraviolet absorbing property. Nano-sized TiO2 has been widely used in photocatalysts, pigments, and cosmetic additives, and toothpaste. These a lot of utilities led to releasing nanometrerials into the environment or discharge to the environment. As a result of ozone layer decrease, ultraviolet light could reach on the earths surface. Because TiO2 has photocatalytic activity, toxic effects could be changed. However little is known about the phototoxicity of TiO2 in aquatic organisms such as Daphnia magna (D. magna). Objectives The aim of this study was to evaluate the effect of light condition and particle size of TiO2 on Daphnia magna. Methods Aucte toxicity test and antioxidant enzyme toxicity test was performed. Acute toxicity test was performed on D. magna using pyrophosphated coated TiO2 (pyro-TiO2P25-70) and uncoated TiO2 (TiO2P25-70) under different light condition such as fluorescent light, ultraviolet-B (UV-B) light and solar light. In addition, antioxidant enzymes such as catalase (CAT), superoxide dismutase (SOD), glutathione s-transferase (GST), and lipid peroxidation (MDA) were analyzed to understand the mechanism of phototoxicity. Results TiO2 toxicity changed with light condition. TiO2 toxicity increased under UV-B and solar light condition. D. magna was more susceptible to TiO2P25-70 than pyro-TiO2P25-70. Antioxidant enzymes, CAT and SOD were similarly expressed to mortality however MDA expression shown reversely expressed pattern compared to CAT and SOD expression. Conclusion TiO2 could be occurred phototoxicity thus when it released to real environmental condition, TiO2 toxicity more increased. Micro size particles more toxic than nano size particle according to particle characteristics and test species. TiO2 could mainly affects test species through oxidative stress mechanisms but other toxic mechanisms such as biological surface coating were also considered. Present study is worth than other toxicity test under laboratory condition because we conducted toxicity test under real environmental condition.