Keywords: 
• copper ions /
• graphene oxide /
• Daphnia magna /
• bioaccumulation /
• oxidative stress response

Abstract: Graphene oxide (GO) has been extensively applied as a novel nanomaterial because of its unique physicochemical properties. It may affect the toxicity of traditional pollutants after entering the environment. In this research, Daphnia magna (D. magna) was selected as a test organism to assay how accumulation of Cu, toxicity and internal antioxidant system in D. magna were affected in the presence of GO. The results show that the adsorption effect of Cu²⁺ on GO was excellent so that Cu²⁺ concentration in test solution was largely reduced. With 1 mg·L^-1 and 2 mg·L^-1 GO, the accumulation of copper in D. magna decreased from 360 μg·g^-1 dry weight to 308 μg·g^-1 and 215 μg·g^-1 dry weight, respectively, after exposed to 19.2 μg·L^-1 Cu²⁺ solutions for 72 h. The presence of GO reduced the toxicity of Cu²⁺ to D. magna and the 72 h-LC₅₀ value of Cu²⁺ was increased from 19.2 μg·L^-1 to 56 μg·L^-1. When D. magna was exposed to Cu²⁺ alone, the SOD activity and GSH content were first induced and then inhibited, and MDA content increased gradually. Variation trend of antioxidant compounds and enzymes activities in D. magna in the presence of GO was similar to that in the absence of GO with single Cu²⁺ exposure, but the activity/content was lower than that after single Cu²⁺ exposure. It is indicated that addition of GO decreased the accumulation of Cu in D. magna, reduced the oxidative damage of Cu²⁺ to D. magna and showed certain alleviative effect to the toxicity of Cu²⁺.