Oxidative stress response of the aquatic macrophyte Hydrilla verticillata exposed to TiO₂ nanoparticles

The present study investigated the effects of titanium dioxide nanoparticles (TiO₂ -NPs) on the oxidative stress response in Hydrilla verticillata. Macrophytes were exposed to different concentrations of TiO₂ -NPs (0 mg/L, 0.01 mg/L, 0.1 mg/L, 1 mg/L, and 10 mg/L) for 24 h, based on currently predicted levels of nano-TiO₂ in surface waters. In addition, TiO₂ -NPs with varying crystalline status were used to assess the potential influence of crystalline phases on oxidative stress responses. The level of hydrogen peroxide (H₂ O₂ ), reduced and oxidized glutathione (GSH and GSSG), and activities of the antioxidative enzymes peroxidase (POD), catalase (CAT), and glutathione reductase (GR) were measured and compared with a bulk counterpart. Although POD was not considered to be active, the results imply an activation of the enzymatic defense system, because increased CAT and GR activities were observed. Exposure to bulk TiO₂ revealed lower enzyme activities at all exposure concentrations, suggesting a nano-specific influence on the antioxidative defense mechanisms in H. verticillata. Moreover, all TiO₂ -NP concentrations resulted in a decreased GSH/GSSG ratio, indicating high GSH-dependent metabolic activity to protect against the destructive effects of reactive oxygen species (ROS) generated during nano-TiO₂ exposure. As the level of H₂ O₂ was solely elevated after exposure to 10 mg/L of P25, it appears plausible that the adaptive metabolic mechanisms of H. verticillata are able to cope with environmentally relevant concentrations of TiO₂ -NPs. Environ Toxicol Chem 2016;35:2859-2866. © 2016 SETAC.