Carbon nanotubes (CNT) are of great commercial interest. Theoretically, during processing and handling of CNT and in abrasion processes on composites containing CNT, inhalable CNT particles might be set free. For hazard assessment, we performed a 90-day inhalation toxicity study with a multiwall CNT (MWCNT) material (Nanocyl NC 7000) according to Organisation for Economic Co-operation and Development test guideline 413. Wistar rats were head-nose exposed for 6 h/day, 5 days/week, 13 weeks, total 65 exposures, to MWCNT concentrations of 0 (control), 0.1, 0.5, or 2.5 mg/m(3). Highly respirable dust aerosols were produced with a proprietary brush generator which neither damaged the tube structure nor increased reactive oxygen species on the surface. Inhalation exposure to MWCNT produced no systemic toxicity. However, increased lung weights, pronounced multifocal granulomatous inflammation, diffuse histiocytic and neutrophilic inflammation, and intra-alveolar lipoproteinosis were observed in lung and lung-associated lymph nodes at 0.5 and 2.5 mg/m(3). These effects were accompanied by slight blood neutrophilia at 2.5 mg/m(3). Incidence and severity of the effects were concentration related. At 0.1 mg/m(3), there was still minimal granulomatous inflammation in the lung and in lung-associated lymph nodes; a no observed effect concentration was therefore not established in this study. The test substance has low dust-forming potential, as demonstrated by dustiness measurements, but nonetheless strict industrial hygiene measures must be taken during handling and processing. Toxicity and dustiness data such as these can be used to compare different MWCNT materials and to select the material with the lowest risk potential for a given application.

Nanocomposites are the dominating class of nanomaterials to come into consumer contact, and were in general assumed to pose low risk. The first data is now emerging on the exposure from nanocomposites, but little is yet known about their hypothetical nanospecific physiological effects, giving ample room for speculation. For the first time, this comprehensive study addresses these aspects in a systematic series of thermoplastic and cementitious nanocomposite materials. Earlier reports that 'chalking', the release of pigments from weathered paints, also occurs for nanocomposites, are confirmed. In contrast, mechanical forces by normal consumer use or do-it-yourself sanding do not disrupt nanofillers (nanoparticles or nanofibers) from the matrix. Detailed evidence is provided for the nature of the degradation products: no free nanofillers are detected up to the detection threshold of 100 ppm. Sanding powders measuring 1 to 80 μm in diameter are identified with the original material, still containing the nanofillers. The potential hazard from aerosols generated by sanding nanocomposites up to the nuisance dust limit is also investigated. In-vivo instillation in rats is used to quantify physiological effects on degradation products from abraded nanocomposites, in comparison to the abraded matrix without nanofiller and to the pure nanofiller. In this pioneering and preliminary evaluation, the hazards cannot be distinguished with or without nanofiller.

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We have developed an instrument, Universal NanoParticle Analyzer (UNPA), for quasi-online measurement of gas-borne nanoparticle agglomerates. The UNPA utilizes a Differential Mobility Analyzer (DMA), a Condensation Particle Counter (CPC), and a Nanoparticle Surface Area Monitor (NSAM, including a unipolar charger combined with an electrometer), to determine the primary particle size and measure the number, surface area, and volume distributions of loose nanoparticle agglomerates. By loose agglomerates we refer to those that can be modeled as clusters of spherical primary particles with open structures and fractal dimensions less than two. The key parameter measured is the UNPA sensitivity, which is defined as the current measured by the NSAM divided by the number concentration measured by the CPC. Our experimental data and theoretical model have shown that the UNPA sensitivity S depends on the particle morphology. The sensitivity S is larger for loose agglomerates than for spheres at a fixed mobility diameter, and S for partly sintered agglomerates is between those for loose agglomerates and spheres. Thus the measured value of S gives a direct indication of the particle morphology. From UNPA sensitivities, the primary particle size is determined using a fitting procedure. Using the model of Lall and Friedlander (2006) for loose agglomerates, the number of primary particles in agglomerates can be computed. Then the surface area and volume of agglomerates can be obtained. Operated under the scanning mode, the UNPA can provide the number, surface area and volume distributions of loose agglomerates in the range of 50 to several hundred nanometers in several minutes.

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