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Impact of natural organic matter on particle behavior and phototoxicity of titanium dioxide nanoparticles
Li, S., H. Ma, L. Wallis, M. Etterson, B. Riley, D. Hoff, AND S. Diamond. Impact of natural organic matter on particle behavior and phototoxicity of titanium dioxide nanoparticles. SCIENCE OF THE TOTAL ENVIRONMENT. Elsevier BV, AMSTERDAM, Netherlands, 542:324-333, (2016).
Ecological risk assessors face increasing demands to assess overwhelmingly increased nanomaterials in the following years. Lots of studies have been and are being conducted, aiming to jointly serve for future regulations of nanomaterials. Though toxic mechanisms have been increasingly addressed in nanotoxicological studies, effective environmental regulations encourage the full range of toxicological investigations, especially those that could contribute to a proper establishment of dose-effect assessment. This effort can be challenged by various confounding factors in the natural environment, of which a particular concern is natural organic matter (NOM). Some studies have investigated the impacts of NOM on the toxicity of nanomaterials. Unfortunately, inconsistent results were reported, mainly due to the existence of various/confounding interaction mechanisms between NOM and nanoparticles. To address this issue, we conducted a series of experiments to study the influences of NOM (TiO2 particle stabilization, UV attenuation, and photosensitization/ROS quenching) on the phototoxicity of TiO2 to D. magna and zebrafish larvae under environmentally relevant solar radiation conditions, and ultimately, we illustrated the relative importance of the above mentioned distinct interactions on the mode of action of photoactive nanomaterials in the presence of NOM in aquatic systems.
Due to their inherent phototoxicity and inevitable environmental release, titanium dioxide nanoparticles (nano-TiO2) are increasingly studied in the field of aquatic toxicology. One of the particular interests is the interactions between nano-TiO2 and natural organic matter (NOM). In this study, a series of experiments was conducted to study the impacts of Suwannee River natural organic matter (SRNOM) on particle behaviors and phototoxicity of nano-TiO2. The impact on particle behavior was both qualitatively and quantitatively examined. A global predictive model for particle behavior was developed with a three-way interaction of SRNOM, TiO2 concentration, and time and an additive effect of ionic strength. Based on power analyses, 96-h bioassays were recommended for nanoparticle-NOM interaction studies. The importance of reactive oxygen species (ROS) quenching of SRNOM was also systematically studied. These experiments were conducted with minimal impacts of other important interaction mechanisms (NOM particle stabilization, NOM UV attenuation, and NOM photosensitization). This study highlighted both the particle stabilization and ROS quenching effects of NOM on nano-TiO2 in an aquatic system. There is an urgent need for representative test materials, together with key environmental factors, for future risk assessment and regulations of nanomaterials.