Enhanced Oxidative Stress and Physiological Damage in Daphnia magna by Copper in the Presence of Nano-TiO2

This study examines the potential hazard of an individual nanomaterial on the Cu biotoxicity to aquatic organisms. Daphnia magna in the absence or presence of nano-TiO2 was exposed to Cu. Maintaining nano-TiO2 at a safe concentration cannot eliminate its potential hazard. The biomarkers superoxide dismutase, catalase, and Na+/K+- ATPase in D. magna were measured. Cu in the presence of nano-TiO2 induced higher levels of oxidative stress and physiological damage because of the sorption of Cu. Nano-TiO2 also caused Na+/K+-ATPase inhibition possibly by impeding the Na+/K+ transfer channel. The correlations among the biomarkers, mortality, and accumulation further showed that the overloading reactive oxygen species generation caused by nano-TiO2 contributed to deeper oxidative stress and physiological regulation, thereby causing greater toxic injury.