Effects of the interaction between TiO(2) with different percentages of exposed {001} facets and Cu(2+) on biotoxicity in Daphnia magna

Anatase TiO(2) nanosheets (NSs) with exposed {001} facets have been widely used because of their high activity and particular surface atomic configuration. However, investigations on their biotoxicity are rare. In this study, bioaccumulation of five different TiO(2) (with 10%, 61%, 71%, 74% and 78% exposed {001} facets), as well as copper and enzyme activities in Daphnia magna, are systematically investigated and rationalized. The results indicated that the addition of Cu(2+) enhanced agglomeration–sedimentation of TiO(2), resulting in the reduction of TiO(2) bioaccumulation by 10% to 26%. TiO(2) nanoparticles (NPs) increased copper bioaccumulation by 9.8%, whereas the other four TiO(2) nanosheets (NSs) decreased it by 43% to 53%, which depended on TiO(2) variant adsorption and free Cu(2+) concentrations in the supernatant. The levels of superoxide dismutase (SOD) enzyme and Na(+)/K(+)-ATPase activities suggested that oxidative stress, instead of membrane damage, was the main toxicity in D. magna. Meanwhile, the SOD enzyme activities increased with decreasing Cu accumulation and increasing Ti accumulation because of the different functions of Cu and Ti in organisms. This research highlighted the important role of the percentage of exposed {001} facets in nanostructured TiO(2) on bioaccumulation and biotoxicity of TiO(2) and Cu(2+) in Daphnia magna.