Correlating Quantitative Measurements of Radical Production by Photocatalytic TiO2 to Daphnia magna Toxicity.

Increased use of titanium dioxide (TiO2 ) nanoparticles in domestic and industrial applications has increased risk for adverse environmental outcomes based on an elevated likelihood of organism exposure. Anatase TiO2 nanoparticle exposure to UV-A radiation in aquatic environments generates radical oxygen species (ROS), which may ultimately be responsible for increased organism toxicity. Herein we identify and measure the two most relevant ROS species, hydroxyl and superoxide radicals, and describe that ROS can be modeled using the highly reactive hydroxyl radical to provide an upper-bound for toxicity. TiO2 nanoparticles were co-exposed to increasing NOM amounts (measured as concentration of dissolved organic carbon (DOC)) and simulated-sunlight UV-A intensities. Radical production rate was determined using fluorescence spectroscopy and positively correlated with increases in TiO2 concentration and UV-A intensity, and negatively correlated to increased DOC concentration. D. magna toxicity was also found to decrease with NOM addition, which is attributed to the decreased radical production rate with increased DOC concentrations. This research demonstrates that the rate of ROS production from simulated-sunlight irradiated TiO2 nanoparticles can be quantified using relatively simple fluorescent techniques. We show that toxicity to TiO2 nanoparticle varies greatly with conditions, and that concentration alone is a poor predictor of toxicity. Describing toxicity per hydroxyl radical measurement may be a more accurate way to describe overall risk. We provide a framework for a simple model to describe toxicity per hydroxyl radical. These conclusions demonstrate the importance of considering exposure conditions as a means of risk management during TiO2 nanoparticle toxicity testing, waste management and regulatory decisions. This article is protected by copyright. All rights reserved.