title: Occupational exposure assessment in carbon nanotube and nanofiber primary and secondary manufacturers.
abstract: RESEARCH SIGNIFICANCE: Toxicological evidence suggests the potential for a wide range of health effects, which could result from exposure to carbon nanotubes (CNTs) and carbon nanofibers (CNFs). The National Institute for Occupational Safety and Health (NIOSH) has proposed a recommended exposure limit (REL) for CNTs/CNFs at the respirable size fraction. The current literature is lacking exposure information, with few studies reporting results for personal breathing zone (PBZ) samples in occupational settings. To address this gap, exposure assessments were conducted at six representative sites identified as CNT/CNF primary or secondary manufacturers.
  
  
  METHODS
  Personal and area filter-based samples were collected for both the inhalable mass concentration and the respirable mass concentration of elemental carbon (EC) as well as CNT structure count analysis by transmission electron microscopy to assess exposures. When possible, full-shift PBZ samples were collected; area samples were collected on a task-based approach.
  
  
  RESULTS
  The vast majority of samples collected in this study were below the proposed REL (7 μg m(-3)). Two of the three secondary manufacturers' surveyed found concentrations above the proposed REL. None of the samples collected at primary manufacturers were found to be above the REL. Visual and microscopy-based evidence of CNTs/CNFs were found at all sites, with the highest CNT/CNF structure counts being found in samples collected at secondary manufacturing sites. The statistical correlations between the filter-based samples for the mass concentration of EC and CNT structure counts were examined. A general trend was found with a P-value of 0.01 and a corresponding Pearson correlation coefficient of 0.44.
  
  
  CONCLUSIONS
  CNT/CNF concentrations were above the proposed NIOSH REL for PBZ samples in two secondary manufacturing facilities that use these materials for commercial applications. These samples were collected during dry powder handling processes, such as mixing and weighing, using fairly large quantities of CNTs/CNFs.
authors.affiliation: Industrywide Studies Branch, Division of Surveillance, Hazard Evaluations, and Field Studies, 4676 Columbia Parkway, MS-R14, Cincinnati, OH 45226, USA. mdahm@cdc.gov
authors.forename: Matthew M
authors.initials: MM
authors.lastname: Dahm
authors.forename: Douglas E
authors.initials: DE
authors.lastname: Evans
authors.forename: Mary K
authors.initials: MK
authors.lastname: Schubauer-Berigan
authors.forename: M Eileen
authors.initials: ME
authors.lastname: Birch
authors.forename: Joseph E
authors.initials: JE
authors.lastname: Fernback
mesh_terms: D000336:Aerosols / Q000032:analysis; D000395:Air Pollutants, Occupational / Q000009:adverse effects / Q000032:analysis*; D000818:Animals; D004784:Environmental Monitoring / Q000379:methods*; D005374:Filtration; D006801:Humans; D007221:Industry / Q000592:standards / Q000706:statistics & numerical data; D019570:Inhalation Exposure / Q000009:adverse effects / Q000032:analysis* / Q000706:statistics & numerical data; D057230:Limit of Detection; D051379:Mice; D046529:Microscopy, Electron, Transmission; D057139:Nanofibers / Q000009:adverse effects / Q000032:analysis*; D037742:Nanotubes, Carbon / Q000009:adverse effects / Q000032:analysis*; D009314:National Institute for Occupational Safety and Health, U.S.; D016273:Occupational Exposure / Q000032:analysis* / Q000592:standards / Q000706:statistics & numerical data; D010316:Particle Size; D014481:United States
chemical_list: D000336:Aerosols; D000395:Air Pollutants, Occupational; D037742:Nanotubes, Carbon