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Phototoxicity and Dosimetry of Nano-scale Titanium Dioxide in Aquatic Organisms
Citation:
DIAMOND, S. A., A. A. BRENNAN, AND J. D. FERNANDEZ. Phototoxicity and Dosimetry of Nano-scale Titanium Dioxide in Aquatic Organisms. Presented at Society of Environmental Toxicology and Chemistry (North America) Meeting, Portland, OR, November 07 - 11, 2010.
Impact/Purpose:
To document research results.
Description:
We have been testing nanoscale TiO2 (primarily Evonik P25) in acute exposures to identify and quantify its phototoxicity under solar simulated radiation (SSR), and to develop dose metrics reflective of both nano-scale properties and the photon component of its potency. Several exposures of medaka larvae have been completed in low ionic-strength water, an approach that consistently yields initial mean initial aggregate sizes of approximately 200 to 300 nm and does not involve the use of aggressive solvents or high-energy (probe sonication) techniques. Under these conditions, the LC50 value is estimated to be 2.42 mg TiO2/L (CI = 2.3 to 2.51), under levels of SSR equal to approximately 25 to 30% of clear-sky summer sunlight (in Duluth, Minnesota). In the absence of SSR the LC50 value is estimated to be ~ 383 mg/L. Reciprocal testing of pre-irradiated TiO2 (without fish), and fish pre-exposed (without of SSR) indicate that phototoxicity is not dependent on either relatively long-lived modification TiO2, or on uptake the material prior to irradiation. Similar approaches have also been used in 48-hr assays with Daphnia magna<'i>, resulting in an LC50 of 216.3 mg TiO2/L (CI = 169 to 288); about an order of magnitude lower relative to medaka. No toxicity was observed at levels up 500 mg TiO2/L under room standard laboratory. These findings provide the basis for a realistic assessment of the importance of solar radiation in estimating hazard and risk for TiO2. Nano scale-specific and photon-based dose metrics will be also be discussed.