Nanoparticles-containing spray can aerosol: characterization, exposure assessment, and generator design

Abstract

This is the first report demonstrating that a commercially available household consumer product produces nanoparticles in a respirable range. This report describes a method developed to characterize nanoparticles that were produced under typical exposure conditions when using a consumer spray product. A well-controlled indoor environment was simulated for conducting spray applications approximating a human exposure scenario. Results indicated that, while aerosol droplets were large with a count median diameter of 22 µm during spraying, the final aerosol contained primarily solid TiO₂ particles with a diameter of 75 nm. This size reduction was due to the surface deposition of the droplets and the rapid evaporation of the aerosol propellant. In the breathing zone, the aerosol, containing primarily individual particles (>90%), had a mass concentration of 3.4 mg/m³, or 1.6 × 10⁵ particles/cm³, with a nanoparticle fraction limited to 170 µg/m³, or 1.2 × 10⁵ particles/cm³. The results were used to estimate the pulmonary dose in an average human (0.075 µg TiO₂ per m² alveolar epithelium per minute) and rat (0.03 µg TiO₂) and, consequently, this information was used to design an inhalation exposure system. The system consisted of a computer-controlled solenoid ‘‘finger’’ for generating constant concentrations of spray can aerosols inside a chamber. Test results demonstrated great similarity between the solenoid ‘‘finger’’-dispersed aerosol compared to human-generated aerosol. Future investigations will include an inhalation study to obtain information on dose–response relationships in rats and to use it to establish a No Effect Exposure Level for setting guidelines for this consumer product.

Keywords::

• Engineered nanoparticles
• ultrafine TiO2
• aerosols
• sprays
• exposure assessment methods
• inhalation studies

Acknowledgements

The authors would like to acknowledge the expert technical assistance on the project of Amy Cumpston, Jared Cumpston, and Donny Leonard. B.T.C. would like to thank Dr. James S. Brown at US EPA for assistance in use of the MPPD model. The findings and conclusions in this paper are those of the authors and do not necessarily represent the views of the National Institute for Occupational Safety and Health or the Consumer Product Safety Commission. The mention of any company names or products does not imply an endorsement by NIOSH or CPSC, nor does it imply that alternative products are unavailable, or unable to be substituted after appropriate evaluation.

Declaration of interest

The authors thank the Consumer Product Safety Commission, which provided additional funding to support the project.