George Pyrgiotakis, Samuel Gass, William Goldsmith, David Frazer, Jane Ma, Walter McKinney, Mark Barger, Bridget Dolash, Vincent Castranova, Philip Demokritou
Ceria nanoparticles are increasingly used for a number of industrial and commercial applications including catalysis, chemical mechanical polishing, UV-shielding, and nanocomposites. As the number of consumers and factory workers exposed to CeO2 nanoparticles increases, the need for a comprehensive toxicological characterization is pressing. While most in-vitro models predict minimal toxicity for nanosized CeO2, preliminary in-vivo animal models using instillation of CeO2 nanoparticles point to fibrogenicity and inflamation. However, to date, most toxicological evidence is limited to in-vitro studies, intratracheal instillation studies which however, do not represent realistic nanoscale exposure scenarios. Here, we present the first ever whole-body systematic animal inhalation study of nano-CeO2. In addition, the use of a nanothin amorphous SiO2 coating as means of mitigating CeO2 toxicity was evaluated as a safer formulation concept. CeO2 (uncoated and SiO2-coated) nanoparticles were synthesized using the Harvard Versatile Engineered Nanomaterial Generating System (VENGES), which enables the synthesis and coating of industrially relevant nanoparticles in the aerosol phase with precise control over primary particle size, aggregation, and aerosol concentration. The generated aerosol was diluted and introduced into a customized exposure chamber, that is fully automated and maintain very stable exposure conditions. The generated CeO2 particles (SiO2 coated and uncoated) were characterized (1) in-situ with respect to aerosol size distribution and number concentration (SMPS), aggregate morphology (TEM, SEM) and (2) ex-situ with respect to crystallinity and chemical composition (XRD, XPS, EDX), surface area (BET), and morphology (TEM, SEM). Exposure atmospheres in the chamber were monitored in real time and characterized with respect to particle number concentration as a function of size (CPC, SMPS), mass concentration (Gravimetric Filter Measurements),aerosol mass size distribution (MOUDI), temperature, humidity, CO, CO2, (Q-Track) and NOx concentrations. Sprague Dawley rats (n=12/group) were exposed to either coated or uncoated CeO2 (2.7 mg/m3, 2 h/day, 4 days). Exposed animals, along with particle free- controls, were sacrificed at either 1 or 84 days post exposure. Pathophysiological analysis was performed and inflammatory and cytotoxic biomarkers were measured in the bronchoalveolar lung lavage (BAL) of the animals. Preliminary results showed that CeO2 is associated with lung inflammation and cytotoxicity as demonstrated by elevated PMN and LDH levels in the BAL fluid. In addition, SiO2 coatings revealed a significant reduction of toxicity, a clear indication of the effectiveness of this safe by design concept.