Computer controlled multi-walled carbon nanotube inhalation exposure system

Abstract

Inhalation exposure systems are necessary tools for determining the dose–response relationship of inhaled toxicants under a variety of exposure conditions. The objective of this project was to develop an automated computer controlled system to expose small laboratory animals to precise concentrations of airborne multi-walled carbon nanotubes (MWCNT). An aerosol generator was developed which was capable of suspending a respirable fraction of multi-walled carbon nanotubes from bulk material. The output of the generator was used to expose small laboratory animals to constant aerosol concentrations up to 12 mg/m³. Particle distribution and morphology of the MWCNT aerosol delivered to the exposure chamber were measured and compared to samples previously taken from air inside a facility that produces MWCNT. The comparison showed the MWCNT generator was producing particles similar in size and shape to those found in a work environment. The inhalation exposure system combined air flow controllers, particle monitors, data acquisition devices, and custom software with automatic feedback control to achieve constant and repeatable exposure chamber temperature, relative humidity, pressure, aerosol concentration, and particle size distribution. The automatic control algorithm was capable of maintaining the mean aerosol concentration to within 0.1 mg/m³ of the selected target value, and it could reach 95% of the target value in less than 10 minutes during the start-up of an inhalation exposure. One of the major advantages of this system was that once the exposure parameters were selected, a minimum amount of operator intervention was required over the exposure period.

Keywords::

• Carbon nanotube
• inhalation exposure
• exposure system
• computer control
• particle generation
• particle distribution
• feedback control

Acknowledgements

The authors gratefully thank Diane Schwegler-Berry for operating the TEM/SEM that provided the images shown in Figure 9, Mitsui & Co. for providing the bulk MWCNT material, and Amy Moseley, Michelle Donlin, and Jared Cumpston for assisting with MOUDI and filter samples taken from the air within the exposure chamber.

Declaration of interest: The findings and conclusions in this report are those of the authors and do not necessarily represent the views of The National Institute for Occupational Safety and Health.