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Carbon Nanotube and Nanofiber Exposure Assessments: An Analysis of 14 Site Visits.

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Title: Carbon Nanotube and Nanofiber Exposure Assessments: An Analysis of 14 Site Visits.
Authors: Dahm, Matthew M.1 mdahm@cdc.gov, Schubauer-Berigan, Mary K.1, Evans, Douglas E.2, Birch, M. Eileen2, Fernback, Joseph E.2, Deddens, James A.1
Source: Annals of Occupational Hygiene. Jul2015, Vol. 59 Issue 6, p705-723. 19p.
Subjects: Carbon, Statistical correlation, Electron microscopy, Environmental monitoring, Nanoparticles, Particles, National Institute for Occupational Safety & Health, Occupational hazards, Environmental exposure, Inhalation injuries, Descriptive statistics
Geographic Terms: United States
Abstract: Recent evidence has suggested the potential for wide-ranging health effects that could result from exposure to carbon nanotubes (CNT) and carbon nanofibers (CNF). In response, the National Institute for Occupational Safety and Health (NIOSH) set a recommended exposure limit (REL) for CNT and CNF: 1 μg m−3 as an 8-h time weighted average (TWA) of elemental carbon (EC) for the respirable size fraction. The purpose of this study was to conduct an industrywide exposure assessment among US CNT and CNF manufacturers and users. Fourteen total sites were visited to assess exposures to CNT (13 sites) and CNF (1 site). Personal breathing zone (PBZ) and area samples were collected for both the inhalable and respirable mass concentration of EC, using NIOSH Method 5040. Inhalable PBZ samples were collected at nine sites while at the remaining five sites both respirable and inhalable PBZ samples were collected side-by-side. Transmission electron microscopy (TEM) PBZ and area samples were also collected at the inhalable size fraction and analyzed to quantify and size CNT and CNF agglomerate and fibrous exposures. Respirable EC PBZ concentrations ranged from 0.02 to 2.94 μg m−3 with a geometric mean (GM) of 0.34 μg m−3 and an 8-h TWA of 0.16 μg m−3. PBZ samples at the inhalable size fraction for EC ranged from 0.01 to 79.57 μg m−3 with a GM of 1.21 μg m−3. PBZ samples analyzed by TEM showed concentrations ranging from 0.0001 to 1.613 CNT or CNF-structures per cm3 with a GM of 0.008 and an 8-h TWA concentration of 0.003. The most common CNT structure sizes were found to be larger agglomerates in the 2-5 μm range as well as agglomerates >5 μm. A statistically significant correlation was observed between the inhalable samples for the mass of EC and structure counts by TEM (Spearman ρ = 0.39, P < 0.0001). Overall, EC PBZ and area TWA samples were below the NIOSH REL (96% were <1 μg m−3 at the respirable size fraction), while 30% of the inhalable PBZ EC samples were found to be >1 μg m−3. Until more information is known about health effects associated with larger agglomerates, it seems prudent to assess worker exposure to airborne CNT and CNF materials by monitoring EC at both the respirable and inhalable size fractions. Concurrent TEM samples should be collected to confirm the presence of CNT and CNF. [ABSTRACT FROM AUTHOR]
Copyright of Annals of Occupational Hygiene is the property of Oxford University Press / USA and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)
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  Data: Recent evidence has suggested the potential for wide-ranging health effects that could result from exposure to carbon nanotubes (CNT) and carbon nanofibers (CNF). In response, the National Institute for Occupational Safety and Health (NIOSH) set a recommended exposure limit (REL) for CNT and CNF: 1 μg m−3 as an 8-h time weighted average (TWA) of elemental carbon (EC) for the respirable size fraction. The purpose of this study was to conduct an industrywide exposure assessment among US CNT and CNF manufacturers and users. Fourteen total sites were visited to assess exposures to CNT (13 sites) and CNF (1 site). Personal breathing zone (PBZ) and area samples were collected for both the inhalable and respirable mass concentration of EC, using NIOSH Method 5040. Inhalable PBZ samples were collected at nine sites while at the remaining five sites both respirable and inhalable PBZ samples were collected side-by-side. Transmission electron microscopy (TEM) PBZ and area samples were also collected at the inhalable size fraction and analyzed to quantify and size CNT and CNF agglomerate and fibrous exposures. Respirable EC PBZ concentrations ranged from 0.02 to 2.94 μg m−3 with a geometric mean (GM) of 0.34 μg m−3 and an 8-h TWA of 0.16 μg m−3. PBZ samples at the inhalable size fraction for EC ranged from 0.01 to 79.57 μg m−3 with a GM of 1.21 μg m−3. PBZ samples analyzed by TEM showed concentrations ranging from 0.0001 to 1.613 CNT or CNF-structures per cm3 with a GM of 0.008 and an 8-h TWA concentration of 0.003. The most common CNT structure sizes were found to be larger agglomerates in the 2-5 μm range as well as agglomerates &gt;5 μm. A statistically significant correlation was observed between the inhalable samples for the mass of EC and structure counts by TEM (Spearman ρ = 0.39, P &lt; 0.0001). Overall, EC PBZ and area TWA samples were below the NIOSH REL (96% were &lt;1 μg m−3 at the respirable size fraction), while 30% of the inhalable PBZ EC samples were found to be &gt;1 μg m−3. Until more information is known about health effects associated with larger agglomerates, it seems prudent to assess worker exposure to airborne CNT and CNF materials by monitoring EC at both the respirable and inhalable size fractions. Concurrent TEM samples should be collected to confirm the presence of CNT and CNF. [ABSTRACT FROM AUTHOR]
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  Data: &lt;i&gt;Copyright of Annals of Occupational Hygiene is the property of Oxford University Press / USA and its content may not be copied or emailed to multiple sites without the copyright holder&#39;s express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract.&lt;/i&gt; (Copyright applies to all Abstracts.)
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        Value: 10.1093/annhyg/mev020
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        Text: English
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        PageCount: 19
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    Subjects:
      – SubjectFull: Carbon
        Type: general
      – SubjectFull: Statistical correlation
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      – SubjectFull: Electron microscopy
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