Changing the dose metric for inhalation toxicity studies: Short-term study in rats with engineered aerosolized amorphous silica nanoparticles

Abstract

Inhalation toxicity and exposure assessment studies for nonfibrous particulates have traditionally been conducted using particle mass measurements as the preferred dose metric (i.e., mg or μg/m³). However, currently there is a debate regarding the appropriate dose metric for nanoparticle exposure assessment studies in the workplace. The objectives of this study were to characterize aerosol exposures and toxicity in rats of freshly generated amorphous silica (AS) nanoparticles using particle number dose metrics (3.7 × 10⁷ or 1.8 × 10⁸ particles/cm³) for 1- or 3-day exposures. In addition, the role of particle size (d₅₀ = 37 or 83 nm) on pulmonary toxicity and genotoxicity endpoints was assessed at several postexposure time points. A nanoparticle reactor capable of producing, de novo synthesized, aerosolized amorphous silica nanoparticles for inhalation toxicity studies was developed for this study. SiO₂ aerosol nanoparticle synthesis occurred via thermal decomposition of tetraethylorthosilicate (TEOS). The reactor was designed to produce aerosolized nanoparticles at two different particle size ranges, namely d₅₀ = ∼30 nm and d₅₀ = ∼80 nm; at particle concentrations ranging from 10⁷ to 10⁸ particles/cm³. AS particle aerosol concentrations were consistently generated by the reactor. One- or 3-day aerosol exposures produced no significant pulmonary inflammatory, genotoxic, or adverse lung histopathological effects in rats exposed to very high particle numbers corresponding to a range of mass concentrations (1.8 or 86 mg/m³). Although the present study was a short-term effort, the methodology described herein can be utilized for longer-term inhalation toxicity studies in rats such as 28-day or 90-day studies. The expansion of the concept to subchronic studies is practical, due, in part, to the consistency of the nanoparticle generation method.

Keywords::

• Amorphous silica particles
• dose metric
• inhalation toxicity studies
• lungs
• nanoparticles
• nanotoxicity studies
• particle aerosols; particle numbers
• particle size distribution

Acknowledgements

This study was performed at DuPont Haskell Global Centers for Health and Environmental Sciences, Newark, DE, and was supported by DuPont Haskell Global Centers for Health and Environmental Sciences. The authors are grateful for the technical advice and specifically particle mass calculations conducted by Dr. Lang Tran and Dr. Debbie Lander. Erin McDermott and Elizabeth Wilkinson provided expert technical support.

Declaration of interest

This study was supported by the DuPont Company. The authors alone are responsible for the content and writing of the paper. The authors report no declarations of interests.