Whole-Body Nanoparticle Aerosol Inhalation Exposures

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-TiO₂ inhalation toxicology studies. Critical components: 1) novel nano-TiO₂ aerosol generator; 2) 0.5 m³ whole-body inhalation exposure chamber; and 3) monitor and control system. Nano-TiO₂ aerosols generated from bulk dry nano-TiO₂ powders (primary diameter of 21 nm, bulk density of 3.8 g/cm³) 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/m³). The mass (M) of the collected particles was determined as M = (M_post-M_pre), where M_pre and M_post are masses of the filter before and after sampling (mg). The mass concentration was calculated as C = M/(Q*t), where Q is sampling flowrate (m³/min), and t is the sampling time (minute). The chamber pressure, temperature, relative humidity (RH), O₂ and CO₂ concentrations were monitored and controlled continuously. Nano-TiO₂ 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.