Effects of Titanium Dioxide Nanoparticles on Photosynthetic and Antioxidative Processes of Scenedesmus obliquus.

Zhou Li,Zhili He,Qingyun Yan,Shanquan Wang,Wei Zhang,Philippe Juneau,Cheng Wang,Yingli Lian,Kui Xu,Longfei Shu

doi:10.3390/plants9121748

Abstract

The effects of the photocatalytic toxicity of titanium dioxide nanoparticle (nano-TiO2) on phytoplankton are well understood. However, as UV light intensity decreases sharply with the depth of the water column, the effects of nano-TiO2 itself on deeper water phytoplankton, such as green algae, need further research. In this research, we investigated the effects of three sizes of TiO2 (10, 50 and 200 nm) on the photosynthetic and antioxidative processes of Scenedesmus obliquus in the absence of UV light. We found that 50 nm and 10 nm TiO2 (10 mg/L) inhibited growth rates and the maximal photosystem II quantum yield compared to the control in Scenedesmus obliquus. The minimal and maximal fluorescence yields, and the contents of reactive oxygen species and lipid peroxidation, increased, indicating that photosynthetic energy/electrons transferred to oxygen and induced oxidative stress in nano-TiO2-treated samples. In addition, we found that aggregations of algae and 10 nm TiO2 were present, which could induce cell membrane disruption, and vacuoles were induced to cope with nano-TiO2 stress in Scenedesmus obliquus. These results enhance our understanding of the effects of nano-TiO2 on the photosynthetic and antioxidative processes of green algae, and provide basic information for evaluating the ecotoxicity of nano-TiO2 in freshwater ecosystems.

Highlights

Since TiO2 nanoparticles are widely used in commercial and industrial fields [1,2], they are inevitably released into freshwater ecosystems [3,4]
We found that nano-TiO2 could directly disrupt the algal cell membrane, and inhibit the oxygen evolution and photosystem II (PSII) activity of S. obliquus, while it induced a series of response mechanisms to cope with these stress conditions
In order to explore the effect of TiO2 (10 mg/L) on the growth of S. obliquus, cell numbers were measured daily and growth rates were calculated during a 72 h TiO2 treatment

Summary

Introduction

Since TiO2 nanoparticles (nano-TiO2 ) are widely used in commercial and industrial fields [1,2], they are inevitably released into freshwater ecosystems [3,4]. It has been found that the concentration of nano-TiO2 ranges from 0.2 μg/L to 16 μg/L [5,6,7], and its modeled concentrations in waste water treatment plant effluents could reach up to 3 mg/L, and this is expected to dramatically increase in natural ecosystems in the future [8,9,10]. As abundant small (around 0.6–200 μm) single or clustered cells with high surface-to-volume ratios suspended in freshwater ecosystems [11], phytoplankton have a high probability of encountering suspended particles, such as TiO2 nanoparticles. The nano-TiO2 pollution in freshwater ecosystems could bring adverse effects on these photosynthetic. A better understanding of the toxicological effects and underlying mechanisms of TiO2 nanoparticles on phytoplankton is essential

Methods

Results

Conclusion