Diminishing toxicity of P25 TiO2 NPs during continuous exposure to freshwater algae Chlorella

Nano-titanium dioxide (Nano-TiO 2 ) has been widely used in industrial manufacture and life science field due to its excellent physical and chemical properties in the past few decades, which makes it inevitably released into the aquatic environment. In freshwater ecosystem, Chlorella is the most commonly used species to study the effect brought by metal oxide nanoparticles. In this work, both the short term and long term effect of P25 TiO 2 on Chlorella were investigated. Here, we found that Nano-TiO 2 would cause serious damage to chlorella in a short period of time, as confirmed by oxidative stress and algal cell morphology. However, different from the short-term condition, the damaging effect was gradually weakened along with the prolongation of exposure time of chlorella to Nano-TiO 2 and the final observed inhibition rate of biomass was nearly zero. In addition, the other important finding of this work is that extracellular polymeric substance (EPS) has remarkably protective effect on algae cells. Algae cells with EPS removed were more vulnerable to nano titanium dioxide and exhibited more difficulties in returning back to normal growth compared with normal algae cells, which might be related to the attachment of nanoparticles to the cell surface.