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/m(3). 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/m(3) 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.

Our laboratory has previously demonstrated that application of an antimicrobial spray product containing titanium dioxide (TiO 2 ) generates an aerosol of titanium dioxide in the breathing zone of the applicator. The present report describes the design of an automated spray system and the characterization of the aerosol delivered to a whole body inhalation chamber. This system produced stable airborne levels of TiO 2 particles with a median count size diameter of 110 nm. Rats were exposed to 314 mg/m 3 min (low dose), 826 mg/m 3 min (medium dose), and 3638 mg/m 3 min (high dose) of TiO 2 under the following conditions: 2.62 mg/m 3 for 2 h, 1.72 mg/m 3 4 h/day for 2 days, and 3.79 mg/m 3 4 h/day for 4 days, respectively. Pulmonary (breathing rate, specific airway resistance, inflammation, and lung damage) and cardiovascular (the responsiveness of the tail artery to constrictor or dilatory agents) endpoints were monitored 24 h post-exposure. No significant pulmonary or cardiovascular changes were noted at low and middle dose levels. However, the high dose caused significant increases in breathing rate, pulmonary inflammation, and lung cell injury. Results suggest that occasional consumer use of this antimicrobial spray product should not be a hazard. However, extended exposure of workers routinely applying this product to surfaces should be avoided. During application, care should be taken to minimize exposure by working under well ventilated conditions and by employing respiratory protection as needed. It would be prudent to avoid exposure to children or those with pre-existing respiratory disease.

Inhalation is the most likely exposure route for individuals working with aerosolizable engineered nano-materials (ENM). To properly perform nanoparticle inhalation toxicology studies, the aerosols in a chamber housing the experimental animals must have: 1) a steady concentration maintained at a desired level for the entire exposure period; 2) a homogenous composition free of contaminants; and 3) a stable size distribution with a geometric mean diameter < 200 nm and a geometric standard deviation σ g < 2.5 5 . The generation of aerosols containing nanoparticles is quite challenging because nanoparticles easily agglomerate. This is largely due to very strong inter-particle forces and the formation of large fractal structures in tens or hundreds of microns in size 6 , which are difficult to be broken up. Several common aerosol generators, including nebulizers, fluidized beds, Venturi aspirators and the Wright dust feed, were tested; however, none were able to produce nanoparticle aerosols which satisfy all criteria 5 .A whole-body nanoparticle aerosol inhalation exposure system was fabricated, validated and utilized for nano-TiO 2 inhalation toxicology studies. Critical components: 1) novel nano-TiO 2 aerosol generator; 2) 0.5 m 3 whole-body inhalation exposure chamber; and 3) monitor and control system. Nano-TiO 2 aerosols generated from bulk dry nano-TiO 2 powders (primary diameter of 21 nm, bulk density of 3.8 g/cm 3 ) were delivered into the exposure chamber at a flow rate of 90 LPM (10.8 air changes/hr). Particle size distribution and mass concentration profiles were measured continuously with a scanning mobility particle sizer (SMPS), and an electric low pressure impactor (ELPI). The aerosol mass concentration (C) was verified gravimetrically (mg/m /min), and t is the sampling time (minute). The chamber pressure, temperature, relative humidity (RH), O 2 and CO 2 concentrations were monitored and controlled continuously. Nano-TiO 2 aerosols collected on Nuclepore filters were analyzed with a scanning electron microscope (SEM) and energy dispersive X-ray (EDX) analysis.In summary, we report that the nano-particle aerosols generated and delivered to our exposure chamber have: 1) steady mass concentration; 2) homogenous composition free of contaminants; 3) stable particle size distributions with a count-median aerodynamic diameter of 157 nm during aerosol generation. This system reliably and repeatedly creates test atmospheres that simulate occupational, environmental or domestic ENM aerosol exposures. Video LinkThe video component of this article can be found at http://www.jove.com/video/50263/ ProtocolThe whole-body nanoparticle inhalation exposure step-by-step operating procedures are described as follows.Note: 1) steps 1 and 3 should be performed in a fume hood; 2) operators must wear appropriate personal protective equipment (respirators, goggles and rubber gloves).

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