Jointed toxicity of TiO2 NPs and Cd to rice seedlings: NPs alleviated Cd toxicity and Cd promoted NPs uptake.

Previous studies have reported that nanoparticles (NPs) and heavy metals are toxic to the environment. However, the jointed toxicity is not yet well understood. This study was aimed to investigate the combined toxicity of TiO2 NPs and the heavy metal cadmium (Cd) to plants. Rice (Oryzasativa L.) was selected as the target plant. The rice seedlings were randomly separated into 12 groups and treated with CdCl2 (0, 10 and 20 mg/L) and TiO2 NPs (0, 10, 100 and 1000 mg/L). The plant height, biomass and root length indicated significant toxicity of Cd to the growth, but TiO2 NPs exhibited the potential ability to alleviate the Cd toxicity. Transmission electron microscopy (TEM) and energy dispersive spectrometer (EDS) confirmed the existence of TiO2 NPs in plants. Elemental analysis of Ti and Cd suggested that the presences of Cd significantly decreased the Ti accumulation in the rice roots in the co-exposure treatments. Interestingly, TiO2 NPs could lower the Cd uptake and distribution in rice roots and leaves. The results of antioxidant enzyme activity, lipid peroxide as well as phytohormones varied in the different treatments. Comparing with the Cd alone treatment, the net photosynthetic rate and chlorophyll content were significantly increased in the co-exposure treatments, suggesting that TiO2 NPs could tremendously reduce the Cd toxicity.