Nano-TiO₂ affects Cu speciation, extracellular enzyme activity, and bacterial communities in sediments

In aquatic ecosystems, titanium dioxide nanoparticles (nano-TiO₂) coexist with heavy metals and influence the existing forms and toxicities of the metal in water. However, limited information is available regarding the ecological risk of this coexistence in sediments. In this study, the effect of nano-TiO₂ on Cu speciation in sediments was investigated using sequential extraction. The microcosm approach was also employed to analyze the effects of the coexistence of nano-TiO₂ and Cu on extracellular enzyme activity and bacterial communities in sediments. Results showed that nano-TiO₂ decreased the organic matter-bound fraction of Cu and increased the corresponding residual fraction Cu. As a result, speciation of exogenous Cu in sediments changed. During the course of the 30-day experiment, the presence of nano-TiO₂ did not affect Cu-induced changes in bacterial community structure. However, the coexistence of nano-TiO₂ and Cu restrained the activity of bacterial extracellular enzymes, such as alkaline phosphatase and β-glucosidase. The degree of inhibition also varied because of the different properties of extracellular enzymes. This research highlighted the importance of understanding and predicting the effects of the coexistence of nanomaterials and other pollutants in sediments.