Computer-automated silica aerosol generator and animal inhalation exposure system.

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 study was to develop an automated computer controlled system to expose small laboratory animals to precise concentrations of uniformly dispersed airborne silica particles. An acoustical aerosol generator was developed which was capable of re-suspending particles from bulk powder. The aerosolized silica output from the generator was introduced into the throat of a venturi tube. The turbulent high-velocity air stream within the venturi tube increased the dispersion of the re-suspended powder. That aerosol was then used to expose small laboratory animals to constant aerosol concentrations, up to 20 mg/m(3), for durations lasting up to 8 h. Particle distribution and morphology of the silica aerosol delivered to the exposure chamber were characterized to verify that a fully dispersed and respirable aerosol was being produced. The inhalation exposure system utilized a combination of airflow controllers, particle monitors, data acquisition devices and custom software with automatic feedback control to achieve constant and repeatable exposure environments. The automatic control algorithm was capable of maintaining median aerosol concentrations to within ±0.2 mg/m(3) of a user selected target concentration during exposures lasting from 2 to 8 h. The system was able to reach 95% of the desired target value in <10 min during the beginning phase of an exposure. This exposure system provided a highly automated tool for conducting inhalation toxicology studies involving silica particles.

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 σg < 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 m(3) 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/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(3)). The mass (M) of the collected particles was determined as M = (Mpost-Mpre), where Mpre and Mpost 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 (m(3)/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.

Computer controlled multi-walled carbon nanotube inhalation exposure system.

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.

Computer-controlled ozone inhalation exposure system.

Accurate systems designed to expose laboratory animals to carefully controlled concentrations of gases and aerosols are an important tool in inhalation toxicology studies. These systems are necessary for determining the dose-response relationship of toxicants under a variety of exposure conditions. The objective of this project was to develop a system, employing feedback control, to expose small laboratory animals to precise concentrations of ozone. This system needed the capability of maintaining exposures at selected levels between 0.2 to 3.0 ppm over specified periods ranging between 1 and 8 h in order to evaluate health risks associated with ozone. The overall goals of this study were (1) to develop a system capable of automatically controlling the ozone exposure levels so the steady-state error remained less than 1% and (2) to optimize the system's response time. By employing a tuned control algorithm, gas monitors, data acquisition, and a custom computer software program, these two goals were realized.

Inhalation exposure of rats to asphalt fumes generated at paving temperatures alters pulmonary xenobiotic metabolism pathways without lung injury.

Asphalt fumes are complex mixtures of various organic compounds, including polycyclic aromatic hydrocarbons (PAHs). PAHs require bioactivation by the cytochrome P-450 monooxygenase system to exert toxic/carcinogenic effects. The present study was carried out to characterize the acute pulmonary inflammatory responses and the alterations of pulmonary xenobiotic pathways in rats exposed to asphalt fumes by inhalation. Rats were exposed at various doses and time periods to air or to asphalt fumes generated at paving temperatures. To assess the acute damage and inflammatory responses, differential cell counts, acellular lactate dehydrogenase (LDH) activity, and protein content of bronchoalveolar lavage fluid were determined. Alveolar macrophage (AM) function was assessed by monitoring generation of chemiluminescence and production of tumor necrosis factor-alpha and interleukin-1. Alteration of pulmonary xenobiotic pathways was determined by monitoring the protein levels and activities of P-450 isozymes (CYP1A1 and CYP2B1), glutathioneS-transferase (GST), and NADPH:quinone oxidoreductase (QR). The results show that acute asphalt fume exposure did not cause neutrophil infiltration, alter LDH activity or protein content, or affect AM function, suggesting that short-term asphalt fume exposure did not induce acute lung damage or inflammation. However, acute asphalt fume exposure significantly increased the activity and protein level of CYP1A1 whereas it markedly reduced the activity and protein level of CYP2B1 in the lung. The induction of CYP1A1 was localized in nonciliated bronchiolar epithelial (Clara) cells, alveolar septa, and endothelial cells by immunofluorescence microscopy. Cytosolic QR activity was significantly elevated after asphalt fume exposure, whereas GST activity was not affected by the exposure. This induction of CYP1A1 and QR with the concomitant down-regulation of CYP2B1 after asphalt fume exposure could alter PAH metabolism and may lead to potential toxic effects in the lung.

Asphalt exposure enhances neuropeptide levels in sensory neurons projecting to the rat nasal epithelium.

Asphalt fumes have been reported to produce nasal irritation in road workers. Since inhaled irritants can increase substance P (SP) production in airway neurons, the effects of asphalt fumes on SP production in trigeminal ganglia (TG) sensory neurons innervating the nasal mucosa were investigated. The effects of asphalt fumes on nasal mucosal innervation were examined by measuring SP and calcitonin-gene-related peptide (CGRP) levels in rat TG neurons projecting to the nasal epithelium. Female Sprague-Dawley rats were exposed to asphalt fumes at 16.0 +/- 8.1mg /m3 for 5 consecutive days, 3.5 h/d. Inflammatory cells were measured in nasal cavity lavage fluid. SP and CGRP immunoreactivity (IR) was measured in the cell bodies of trigeminal ganglion sensory neurons projecting to the nasal cavity. A significant increase in neutrophils and macrophages was observed after asphalt fume exposure indicating an inflammatory response in the nasal cavity. The percentage of SP-IR neurons increased significantly in the asphalt-exposed rats, and the proportion of CGRP-IR neurons was also elevated following asphalt exposure. These results indicate that exposure to asphalt fumes produces inflammation and increases the levels of SP and CGRP in TG neurons projecting to the nasal epithelium. The findings are consistent with asphalt-induced activation of sensory C-fibers in the nasal cavity. Enhanced sensory neuropeptide release from nerve terminals in the nasal cavity may produce neurogenic inflammation associated with nasal irritation following exposure to asphalt fumes.