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Size distribution and characteristics of aerosol released from unrefined carbon nanotube material.
Xiong JQ; Heikkinen MSA; Cohen BS
Proceedings of the Interagency Workshop on the Environmental Implications of Nanotechnology, September 5-7. 2007, Washington, DC. Washington, DC: Environmental Protection Agency, 2007 Sep; :21, 119-124
Carbon nanotubes (CNTs) are among the most dynamic and fast-growing nanomaterials due to their novel properties. The potential of human exposure to this new type of material in the workplace, as well as in the general environment, is rising, and its impact on human health is of great concern. In this study, we have investigated the size distributions of airborne CNT particles that were laboratory-generated by using a vortex agitator and dispersed with a very low flow of HEPA-filtered air. The number-weighted particle size distributions were monitored by a 13-stage Electrical Low Pressure Impactor (ELPI) and a 6-stage Integrating Screen Diffusion Battery (ISDB). Several industrial-grade unrefined CNT samples (raw materials) of various types have been examined, including single-walled, double-walled, and multiwalled nanotubes. The CNT samples were collected onto the aluminum substrates placed on each stage of the ELPI. For ISDB sampling, the samples were collected on an array of stainless steel screens, as well as mica discs attached on the wall between the screens. The experimental data demonstrated that all types of CNT raw materials examined can be dispersed into the air to a significant extent. The sizes of particles generated were widely distributed across all 13 stages of the ELPI, including the filter stage ranging from 7 nm to 10 um. The ISDB results showed that the particles released from CVD-SWCNT material (HP-grade, Helix, TX) have a solo peak under 10 nm, with a mode of 2.5 nm and GSD of 1.24 in number-weighted distributions. The experimental data also showed that the size distributions varied with the type of CNTs and with the methods by which they were manufactured. The image analysis results by Atomic Force Microscopy showed that the CNTs tend to agglomerate rather than exist as single particles, physically. These results suggest that CNTs can possibly become airborne under certain agitation conditions during manufacturing and handling processes and can expose workers via inhalation and dermal absorption. As deposition efficiency and sites of inhaled particles within the respiratory system largely depend on particle size distribution, the deposition pattern of agglomerated CNT should be similar to those larger, equivalent-sized nonagglomerated particles. Nevertheless, entrained particles depositing on/in the deep lung surfaces of the bronchioles or alveoli will contact pulmonary surfactants in the surface hypophase and the agglomerated CNT are likely to (ultimately) be de-agglomerated. Therefore, to investigate human exposure to airborne CNTs, the full-size range of inhalable particles must be taken into account.
Nanotechnology; Particle-aerodynamics; Particulates; Particulate-dust; Aerosol-particles; Aerosols; Airborne-particles
Proceedings of the Interagency Workshop on the Environmental Implications of Nanotechnology, September 5-7. 2007, Washington, DC
University of Pittsburgh at Pittsburgh