Titanium Dioxide Nanoparticles Induce Root Growth Inhibition in Soybean Due to Physical Damages

Abstract

Titanium dioxide (TiO2) nanoparticles (NPs) are the most widely released nanomaterials in the environment and are considered an emerging contaminant. Although the phytotoxicity mechanism of TiO2 NPs on plants involves the elevated generation of reactive oxygen species (ROS), it is still not well established in soybean. Herein, we evaluated the effects of 250–1000 mg L−1 TiO2 NPs on seed germination, growth, content of ROS, lipid peroxidation, and activity of antioxidant enzymes in roots of soybean plants. Our data revealed that up to 1000 mg L−1 TiO2 NPs did not affect soybean seed germination. Transmission electron microscopy images and determinations of zeta potential and hydrodynamic diameter of a suspension of TiO2 NPs demonstrated that they form aggregates, favoring their adsorption to the root surface with consequent physical damage. The main deleterious effects noted on roots were reduced cell viability, reduced root hair number, striated aspect of root apexes, and reduced fresh and dry weights of roots. In disagreement with other studies, plant exposure to TiO2 NPs reduced the level of total ROS and lipid peroxidation, probably due to increased superoxide dismutase (SOD) activity. Altogether, our data suggest that the toxicity mechanism of TiO2 NPs on soybean roots involves physical damage resulting from their adsorption to the root surface, but not the generation of ROS.