Effects of Titanium Dioxide Nanoparticles on Photosynthetic and Antioxidative Processes of Scenedesmus obliquus

The effects of the photocatalytic toxicity of titanium dioxide nanoparticle (nano-TiO2) on phytoplankton are well understood. However, as UV light intensity decreases sharply with the depth of the water column, the effects of nano-TiO2itself on deeper water phytoplankton, such as green algae, need further research. In this research, we investigated the effects of three sizes of TiO2(10, 50 and 200 nm) on the photosynthetic and antioxidative processes ofScenedesmus obliquusin the absence of UV light. We found that 50 nm and 10 nm TiO2(10 mg/L) inhibited growth rates and the maximal photosystem II quantum yield compared to the control inScenedesmus obliquus. The minimal and maximal fluorescence yields, and the contents of reactive oxygen species and lipid peroxidation, increased, indicating that photosynthetic energy/electrons transferred to oxygen and induced oxidative stress in nano-TiO2-treated samples. In addition, we found that aggregations of algae and 10 nm TiO2were present, which could induce cell membrane disruption, and vacuoles were induced to cope with nano-TiO2stress inScenedesmus obliquus. These results enhance our understanding of the effects of nano-TiO2on the photosynthetic and antioxidative processes of green algae, and provide basic information for evaluating the ecotoxicity of nano-TiO2in freshwater ecosystems.Keywords:titanium dioxide nanoparticle;photosynthesis;oxidative stress;Scenedesmus obliquus