Animal inhalation studies have reported that adverse pulmonary, cardiovascular, and immune reactions may result from exposure to multi-walled carbon nanotubes (MWCNTs). At the present time, however, there is little guidance for adequate sampling and characterization of MWCNT aerosols for evaluating exposures and obtaining an applicable dose metric for risk assessment. This is mainly because MWCNTs tend to agglomerate and form complex structures making them difficult to characterize. To address this problem, we conducted detailed sampling and characterization studies of MWCNTs that had similar particle morphologies to those found in the workplace. Representative samples were collected using filters, a cascade impactor, and direct reading instruments, and they were used for microscopic observation, gravimetric analysis, and real-time monitoring. Particle number distributions on a filter (0.008-0.10 particles/microm2), and mass distributions using an impactor (0.1-0.3 mg on peak stages) were determined. Microscopic analyses indicated that MWCNTs can be classified into three shape categories: irregular, isometric, and fibrous particle structures. Each particle structure contained a mean of 18 nanotubes, and 1 microg of MWCNTs contained 2.7 x 106 particle structures composed of 4.9 x 107 individual nanotubes. Impactor measurements showed that the mass median aerodynamic diameter of the aerosol was 1.5 microm with a geometric standard deviation of 1.67. The shape factor of individual fibers was 1.94-2.71, and the isometric particles had an effective density of 0.71-0.88 g/cm3. Results also indicated that real-time particle number counts were realistic, but without an index of agglomeration, they were insufficient for adequate risk assessment. Information from this study can be used to estimate initial lung burden and to design an improved lung deposition model that considers three individual MWCNT particle shapes. The described methods can be used as guidance for sampling and characterizing other engineered nanoparticles.
Toxicology; Nanotechnology; Aerosols; Laboratory-techniques; Exposure-assessment; Exposure-levels; Inhalation-studies; Pulmonary-system; Lung-burden; Dose-response; Risk-analysis; Sampling; Aerosol-sampling; Particulate-sampling-methods; Morphology; Microscopic-analysis; Gravimetric-analysis; Particle-aerodynamics; Particle-counters; Physical-chemistry; Physical-properties; Physiological-measurements; Analytical-models; Analytical-processes
The Toxicologist. Society of Toxicology 52nd Annual Meeting and ToxExpo, San Antonio, Texas, March 10-14, 2013