TiO2 nanoparticles dose, application method and phosphorous levels influence genotoxicity in Rice (Oryza sativa L.), soil enzymatic activities and plant growth.

The present study focused on investigating the effect of titanium dioxide nanoparticles (TiO2NPs) on rice (Oryza sativa L.) growth and changes in soil health in two contrasting soil textures (silt-loam and clay). Moreover, response of rice to different methods of TiO2NPs application and phosphorous fertilizer levels were also evaluated. For toxicity assessment, pot experiment was carried out. TiO2NPs (0, 500, 750 mg kg-1) were applied and plants were grown till vegetative stage. After harvesting, physiological parameters, stress assay, soil microbial and enzymatic activities were determined. Based on the results of toxicity study, impact of three methods of TiO2NPs application (foliar, irrigation, soil) and four phosphorous fertilizer levels (0, 10, 20, 40 mg kg-1) on rice growth were assessed. During the 1st phase, results showed an adverse effect of TiO2NPs on plant growth and soil microorganisms in both soil textures at 750 mg kg-1. The H2O2 production, lipid peroxidation and leaf membrane injury index were increased by 4.3-, 2.4-, and 1.9-folds in clay soil upon 750 mg kg-1 TiO2NPs application. Likewise, at the same level of TiO2NPs; microbial biomass, dehydrogenase, and respiration were decreased by 0.91-, 0.79-, and 0.78- folds respectively. In 2nd phase, maximum shoot length, biomass, phosphorous uptake and rice grain protein content were observed under application of TiO2NPs (500 mg kg-1) through irrigation method in combination with 40 mg P kg-1. However, 20 and 40 mg P kg-1 performed equally well upon TiO2NPs application and the results were not statistically significant. The results suggest that 750 mg kg-1 of TiO2NPs negatively affect plant growth and soil enzymatic activities. Moreover, combined application of TiO2NPs (500 mg kg-1) through irrigation and 20 mg P kg-1 is recommended to be the optimum for growth of rice plant.