In Vitro Analyses of Effect of Light on Toxicity of Titanium Dioxide Nanoparticles to Tetrahymena pyriformis Using Fourier Transform Infrared Spectra

The wide application of titanium dioxide nanoparticles (TiO2 NPs) has caused a large number of TiO2 NPs to be released into the water environment without treatment, which would inevitably result in unexpected toxic damage to aquatic animals. The objects of this research were to discuss the toxic effects of TiO2 NPs to Tetrahymena pyriformis (T. pyriformis) under dark and light conditions. The Fourier transform infrared (FTIR) spectra were utilized to investigate the biochemical constituent changes of T. pyriformis under the exposure of TiO2 NPs. The results showed that illumination had little effect on the cell numbers of T. pyriformis after 24hr exposure at 5mg/L of TiO2 concentration. However, the cell viability of TiO2 NP-exposed T. pyriformis under light illumination (81.4%) decreased compared with that in the dark environment (96.1%). The FTIR results showed that the typical absorption band of the CH2 asymmetric stretching vibration shifted from 2924.64 to 2925.49cm(-1) in the dark, which indicated an increase in membrane fluidity without illumination. A decreased intensity (p<0.05) was observed in amide I and amide II from 98.57 +/- 9.62 and 41.88 +/- 3.63 to 75.65 +/- 4.07 and 25.25 +/- 1.12 in the irradiated T. pyriformis, respectively, which suggested that the coexistence of TiO2 NPs and light could induce an obvious decrease of protein. In the light condition, the overproduction of ROS led to the breakdown of balance of the oxidative/antioxidative system, resulting in the lipid peroxidation and the death of cells. The results further reveal that TiO2 NPs under light conditions are more toxic than in the dark.