Citation:

Al-Abed, S., J. Virkutyte, J. Ortenzio, R. McCarrick, L. Degn, R. Zucker, N. Coates, K. Cleveland, H. Ma, S. Diamond, K. Dreher, AND W. Boyes. Environmental aging alters AI(OH)3 coating of TiO2 nanoparticles enhancing their photocatalytic and phototoxicity activities. Environmental Science: Nano. RSC Publishing, Cambridge, Uk, , N/A, (2016).

Impact/Purpose:

A comprehensive evaluation of the potential for engineered nanomaterials (ENM) to cause unintended effects on human health or the environment must include consideration of its product life cycle, comprising manufacture, application, and eventual disposal (NRC, 2013). Particular areas of concern are assessing the potential for release and dispersion of nanomaterials across this life cycle, determining the potential transformations of ENM in the environment, and identifying subsequent changes in ENM reactivity.

Description:

It is important to evaluate the potential effects of engineered nanomaterials (ENM) across the lifecycle of nanomaterial-enabled products including transformations in the environment that mayeither gain or lose functional properties. For example, uncoated titanium dioxide (Ti02) ENMsexposed to UV radiation generate reactive oxygen species (ROS). As a component of sunscreenformulations, Ti02 ENM are coated with materials such as Al(OH)3 to prevent ROS fromcausing oxidative damage to skin. We investigated the stability of the Al(OH)3 coating byexposing 25 nm Al(OH)3•Ti02 ENM to simulated swimming pool water (SPW) for 0 minutes(min), 45 min, 1 day, 3 days, 10 days, or 14 days. Electron microscopy and spectroscopyindicated that the aging of Al(OH)3•Ti02 caused a redistribution of the Al(OH)3 particle coatingand the formation of hydroxyl radicals upon exposure to UV light. Increased photocatalyticactivity of aged particles was detected with the thiobarbituric acid reactive species (TBARS)procedure, but not by other assays of photocatalysis. Phototoxic tissue damage was evaluated bymeasuring cytotoxicity in a human-derived retinal pigment epithelium cell line (ARPE-19). Agedparticles showed significantly greater phototoxicity than un-aged ENM with up to 30% greatercytotoxicity under UVA irradiation. However, no significant statistical differences inphototoxicity were observed based on the duration of aging. Photocatalytic activity andphototoxicity of aged coated Ti02 was substantially less than that of the positive control-uncoated P25 Ti02. In summary, the aging of Al(OH)3•Ti02 ENM in SPW redistributed thecapping shield and reduced its protective properties to increase particle reactivity and potentialphototoxicity.452

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