Occupational Exposure to Carbon Nanotubes and Nanofibers

observed to be task-specific and short-term in duration,with exposure concentrations (frequentlyreported as particle number or mass concentrations)found to exceed background exposure measurementswhen appropriate engineering controlsare not used to reduce exposures [Maynard et al.2004; Methner et al. 2007; Han et al. 2008a; Bello etal. 2009; Tsai et al. 2009; Bello et al. 2010; Evans et al.2010; Johnson et al. 2010; Lee et al. 2010; Cena andPeters 2011; Dahm et al. 2011]. Results from studiesalso suggest that the airborne concentration andthe physical-chemical characteristics of particles(e.g., discrete versus agglomerated CNT) releasedwhile handling CNT may vary significantly withproduction batch and work process. Comprehensiveworkplace exposure evaluations are needed tocharacterize and quantify worker exposure to CNTand CNF at various job tasks and operations, andto determine what control measures are the mosteffective in reducing worker exposures.The findings of adverse respiratory effects (i.e., pulmonaryfibrosis, granulomatous inflammation) andsystemic responses in animals indicate the needfor protective measures to reduce the health risk toworkers exposed to CNT and CNF. Availableevidence also indicates that the migration of MW-CNT into the intrapleural space could potentiallyinitiate mesothelial injury and inflammation thatover time cause pleural pathology, including mesothelioma.Long-term inhalation studies are neededto determine whether CNT and CNF of specificdimension and chemistry can cause cancer inlaboratory animals at doses equivalent to potentialworkplace exposures. In addition, the potential formigration of CNT through the lungs and for accumulationin the intrapleural space with time afterinhalation requires further investigation. Until resultsfrom animal research studies can fully explainthe mechanisms in which inhalation exposure toCNT and CNF cause adverse lung effects and possiblesystemic effects, all types of CNT and CNFshould be considered an occupational respiratoryhazard, and the following actions should be takento minimize health concerns:1. Minimize workplace exposures.2. Establish an occupational health surveillanceprogram for workers exposed to CNT and CNF(Section 6, Appendix B).NIOSH CIB 65 • Carbon Nanotubes and Nanofibers35