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1.
Am J Ind Med ; 58(5): 494-508, 2015 May.
Article in English | MEDLINE | ID: mdl-25675894

ABSTRACT

BACKGROUND: Airborne fiber size has been shown to be an important factor relative to adverse lung effects of asbestos and suggested in animal studies of carbon nanotubes and nanofibers (CNT/CNF). MATERIALS AND METHODS: The International Standards Organization (ISO) transmission electron microscopy (TEM) method for asbestos was modified to increase the statistical precision of fiber size determinations, improve efficiency, and reduce analysis costs. Comparisons of the fiber size distributions and exposure indices by laboratory and counting method were performed. RESULTS: No significant differences in size distributions by the ISO and modified ISO methods were observed. Small but statistically-significant inter-lab differences in the proportion of fibers in some size bins were found, but these differences had little impact on the summary exposure indices. The modified ISO method produced slightly more precise estimates of the long fiber fraction (>15 µm). CONCLUSIONS: The modified ISO method may be useful for estimating size-specific structure exposures, including CNT/CNF, for risk assessment research.


Subject(s)
Air Pollutants, Occupational/analysis , Asbestos/analysis , Microscopy, Electron, Transmission/methods , Nanofibers/analysis , Nanotubes, Carbon/analysis , Occupational Exposure/analysis , Particle Size , Environmental Monitoring/methods , Humans , Risk Assessment
2.
Acc Chem Res ; 46(3): 642-9, 2013 Mar 19.
Article in English | MEDLINE | ID: mdl-23210709

ABSTRACT

Carbon nanotubes (CNTs) are carbon atoms arranged in a crystalline graphene lattice with a tubular morphology. CNTs exhibit high tensile strength, possess unique electrical properties, are durable, and can be functionalized. These properties allow applications as structural materials, in electronics, as heating elements, in batteries, in the production of stain-resistant fabric, for bone grafting and dental implants, and for targeted drug delivery. Carbon nanofibers (CNFs) are strong, flexible fibers that are currently used to produce composite materials. Agitation can lead to aerosolized CNTs and CNFs, and peak airborne particulate concentrations are associated with workplace activities such as weighing, transferring, mixing, blending, or sonication. Most airborne CNTs or CNFs found in workplaces are loose agglomerates of micrometer diameter. However, due to their low density, they linger in workplace air for a considerable time, and a large fraction of these structures are respirable. In rat and mouse models, pulmonary exposure to single-walled carbon nanotubes (SWCNTs), multi-walled carbon nanotubes (MWCNTs), or CNFs causes the following pulmonary reactions: acute pulmonary inflammation and injury, rapid and persistent formation of granulomatous lesions at deposition sites of large CNT agglomerates, and rapid and progressive alveolar interstitial fibrosis at deposition sites of more dispersed CNT or CNF structures. Pulmonary exposure to SWCNTs can induce oxidant stress in aortic tissue and increases plaque formation in an atherosclerotic mouse model. Pulmonary exposure to MWCNTs depresses the ability of coronary arterioles to respond to dilators. These cardiovascular effects may result from neurogenic signals from sensory irritant receptors in the lung. Pulmonary exposure to MWCNTs also upregulates mRNA for inflammatory mediators in selected brain regions, and pulmonary exposure to SWCNTs upregulates the baroreceptor reflex. In addition, pulmonary exposure to MWCNTs may induce levels of inflammatory mediators in the blood, which may affect the cardiovascular system. Intraperitoneal instillation of MWCNTs in mice has been associated with abdominal mesothelioma. MWCNTs deposited in the distal alveoli can migrate to the intrapleural space, and MWCNTs injected in the intrapleural space can cause lesions at the parietal pleura. However, further studies are required to determine whether pulmonary exposure to MWCNTs can induce pleural lesions or mesothelioma. In light of the anticipated growth in the production and use of CNTs and CNFs, worker exposure is possible. Because pulmonary exposure to CNTs and CNFs causes inflammatory and fibrotic reactions in the rodent lung, adverse health effects in workers represent a concern. NIOSH has conducted a risk assessment using available animal exposure-response data and is developing a recommended exposure limit for CNTs and CNFs. Evidence indicates that engineering controls and personal protective equipment can significantly decrease workplace exposure to CNTs and CNFs. Considering the available data on health risks, it appears prudent to develop prevention strategies to minimize workplace exposure. These strategies would include engineering controls (enclosure, exhaust ventilation), worker training, administrative controls, implementation of good handling practices, and the use of personal protective equipment (such as respirators) when necessary. NIOSH has published a document containing recommendations for the safe handling of nanomaterials.


Subject(s)
Chemical Safety , Lung Injury/prevention & control , Nanofibers/toxicity , Nanotubes, Carbon/toxicity , Occupational Exposure , Animals , Cells, Cultured , Lung/drug effects , Mice , Models, Animal , Nanofibers/chemistry , Nanotubes, Carbon/chemistry , Rats , Risk Assessment
3.
Am J Ind Med ; 55(5): 395-411, 2012 May.
Article in English | MEDLINE | ID: mdl-22392774

ABSTRACT

There is still uncertainty about the potential health hazards of carbon nanotubes (CNTs) particularly involving carcinogenicity. However, the evidence is growing that some types of CNTs and nanofibers may have carcinogenic properties. The critical question is that while the carcinogenic potential of CNTs is being further investigated, what steps should be taken to protect workers who face exposure to CNTs, current and future, if CNTs are ultimately found to be carcinogenic? This paper addresses five areas to help focus action to protect workers: (i) review of the current evidence on the carcinogenic potential of CNTs; (ii) role of physical and chemical properties related to cancer development; (iii) CNT doses associated with genotoxicity in vitro and in vivo; (iv) workplace exposures to CNT; and (v) specific risk management actions needed to protect workers.


Subject(s)
DNA Damage , Inhalation Exposure/adverse effects , Lung/drug effects , Nanotubes, Carbon/toxicity , Neoplasms/etiology , Occupational Exposure/adverse effects , Pulmonary Fibrosis/chemically induced , Animals , Humans , Inhalation Exposure/prevention & control , Lung/pathology , Nanotubes, Carbon/chemistry , Occupational Exposure/prevention & control , Risk Management
4.
J Occup Environ Med ; 50(5): 517-26, 2008 May.
Article in English | MEDLINE | ID: mdl-18469620

ABSTRACT

OBJECTIVE: Health authorities, employers, and worker representatives are increasingly faced with making decisions about occupational health surveillance of workers potentially exposed to engineered nanoparticles. This article was developed to identify options that can be considered. METHODS: The published scientific literature on health effects from engineered and incidental nanoparticles and the principles of occupational health surveillance were reviewed to describe possible options and the evidence base for them. RESULTS: Various options for occupational health surveillance were identified. The options ranged from no action targeted to nanotechnology workers to an approach that includes documentation of the presence of engineered nanoparticles, identification of potentially exposed workers, and general and targeted medical testing. CONCLUSIONS: Although the first priority should be to implement appropriate primary preventive measures, additional efforts to monitor employee health may be warranted. Continued research is needed, and the collection of such information for exposure registries may be useful for future epidemiologic studies.


Subject(s)
Nanoparticles , Occupational Exposure , Population Surveillance/methods , Safety Management/methods , Environmental Monitoring , Evidence-Based Medicine , Humans , Nanoparticles/adverse effects , Nanoparticles/analysis , Occupational Diseases/prevention & control , Occupational Exposure/adverse effects , Occupational Exposure/prevention & control , Occupational Medicine/methods
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