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Researchers Study Worker Exposures at Carbon Nanotube Production Facility

Release Date: May 6, 2016

Carbon nanotubes (CNTs) are finding increased use in a variety of commercial applications, such as textiles, electronic devices, and sporting goods. Animal studies show certain types of CNTs can cause lung cancer and other respiratory effects, and laboratory investigations indicate that CNTs can cause genetic defects in human lung cells. Very little data is available on human health effects of CNT exposure, although the National Institute for Occupational Safety and Health (NIOSH) is conducting health (epidemiological) studies of workers at commercial CNT production facilities.

Most of the worker exposures conducted to date examined exposures in research and development (R&D) environments, where relatively small amounts of CNTs are used compared to the amounts used in production facilities. And of the few exposure studies conducted in production facilities, very little full-shift personal breathing zone data has been collected of the type which is typical of the sampling conducted in most industrial hygiene surveys. Researchers from the Netherlands, Belgium, and the United States have published the results of a study designed to fill in these data gaps in the April 2016 issue of Annals of Occupational Hygiene. The paper is entitled “Occupational Exposure to Multi-Walled Carbon Nanotubes During Commercial Production Synthesis and Handling,” and was authored by E. Kujpers, C. Bekker, W. Fransman, D. Brouwer, P. Tromp, J. Vlaanderen, L. Godderis, P. Hoet, Q. Lan, D. Silverman, R. Vermeulen, and A. Pronk.

Investigators measured worker exposures to multi-walled CNTs (MWCNTs) in the production area, an office that was connected to the production area, and a R&D laboratory, which was separate from both, at a commercial plant which produced more than 100 kilograms of MWCNTs per day. Workers in the lab conducted tasks that generally involved handling 500 grams or less of MWCNTs. Office workers did not handle MWCNTs, but were monitored to determine if there was any migration of MWCNTs from the production or R&D areas into the office area. Sophisticated laboratory analyses, such as elemental carbon (EC) analysis and electron microscopy, were utilized to analyze the samples collected in the breathing zones of the workers. EC analysis was used as an indicator of the concentration of MWCNT total (inhalable) dust in the worker breathing zones, and electron microscopy was used to determine the size and shape of the MWCNTs collected on the filters.

Results of the study included the following:

There is no Occupational Safety and Health Administration (OSHA) permissible exposure limit (PEL) for MWCNTs, although NIOSH has adopted a Recommended Exposure Limit (REL) of 1 ug/m3 of respirable MWCNT dust measured using the EC method. The NIOSH REL is based upon keeping exposure below the limit of detection of the analytical method. The investigators tried to get a handle on how much of the measured total (inhalable) MWCNT dust collected on the filters would be in the respirable range, and although the estimated respirable concentrations were lower, many were still above the NIOSH REL.

There are two important observations to note about the study. First, knowledge of the tasks and areas associated with the highest MWCNT exposures allows the plant to focus efforts on the implementation of control measures where they are needed the most. Second, the study indicates that more research is needed in developing monitoring methods and interpretation of the health effects of the measured exposures.

A free abstract of “Occupational Exposure to Multi-Walled Carbon Nanotubes During Commercial Production Synthesis and Handling” can be accessed by searching the Annals of Occupational Hygiene website at http://annhyg.oxfordjournals.org/. The full text can be downloaded for a fee.

For more information on CNTs, see NIOSH publication Current Intelligence Bulletin 65. Occupational Exposure to Carbon Nanotubes at http://www.cdc.gov/niosh/docs/2013-145/pdfs/2013-145.pdf and the NIOSH “Nanotechnology” resource website at http://www.cdc.gov/niosh/topics/nanotech/.

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