Impact of Titanium Dioxide Nanoparticles on Cd Phytotoxicity and Bioaccumulation in Rice (Oryza sativa L.)

The impact of engineered nanoparticles (ENPs) on the migration and toxicity of coexisting pollutants is still unclear, especially in soil media. This study aims to evaluate the impact of titanium dioxide nanoparticles (TiO₂ NPs) on the phytotoxicity of cadmium (Cd) to Oryza sativa L., and the migration of cadmium (Cd) in the soil-rice system. Three different Cd stress groups (C1 group: 1.0 mg kg^-1, C2 group: 2.5 mg kg^-1 and C3 group: 5.0 mg kg^-1) were set in the pot experiment, and the target concentration of TiO₂ NPs in each group were 0 mg kg^-1 (T0), 50 mg kg^-1 (T1), 100 mg kg^-1 (T2) and 500 mg kg^-1 (T3). Plant height and biomass decreased with the increasing of Cd content in paddy soil. TiO₂ NPs could lower the phytotoxicity of Cd in terms of the changes in the morphological and biochemical characteristics, especially in the tillering and booting stage. In the tillering stage, TiO₂ NPs addition caused a significant increase in plant height, biomass and the total chlorophyll content in the leaves of Oryza saliva L. In the booting stage, TiO₂ NPs addition caused a 15% to 32% and 24% to 48% reduction of malondialdehyde (MDA) content for the C2 and C3 group, respectively, compared to that of the respective control treatment (T0). TiO₂-NPs addition reduced the activity of peroxidase (POD) in the leaves in the booting and heading stage, and the activity of catalase (CAT) in the tillering stage. In the C1 and C2 group, the grain Cd content in the 100 and 500 mg kg^-1 TiO₂ NPs treatments reached 0.47-0.84 mg kg^-1, obviously higher than that of the treatment without TiO₂ NPs (0.27-0.32 mg kg^-1), suggesting that TiO₂-NPs could promote Cd migration in the soil-rice system.