Effects of aggregation and settling of photoactive TiO2 nanoparticles on Microcystis aeruginosa and extracellular matters release

Owing to their diverse applications, TiO₂-nanoparticles have been extensively discharged into the aquatic environment, posing serious threats to aquatic life and human health. Meanwhile, the aquatic organisms such as cyanobacteria affect the mobility and fate of the nanoparticles, in turn, these aquatic organisms also may be influenced by the nanoparticles, and which further elicits more hazard to ecosystem. In this study, the different concentration of TiO₂ nanoparticles were added into the algal solution to observe the status of TiO₂ nanoparticles and assess their influences, especially for photocatalytic toxicity on algal growth. The results demonstrated that algal cells and extracellular polymeric substances (EPS) simultaneously affected the TiO₂ aggregation and settling in algae culture. In addition, TiO₂ NPs inhibited the growth of algal cells through the multiple effects on the light adsorption, photosynthetic activity, oxidative stress and lipid peroxidation. Particularly, the reactive oxygen species generated by photoactive TiO₂ NPs caused the changes of EPS and microcystin-LR (MC-LR) release, and these extracellular matters were crucial intermediate to the state of TiO₂ NPs and algal cells growth. This study will not only be significant for understanding TiO₂ behavior in the real aquatic environment but also be helpful for exploring the effects of TiO₂ nanoparticles on cyanobacteria, especially for the released extracellular matters.