Occupational Exposure to Carbon Nanotubes and Nanofibers

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composite materials with local exhaust ventilationturned off. Four potential exposure-modifying factorswere assessed: (1) by composite type, (2) drillingrpm (low and high), (3) thickness of the composite,and (4) dry versus wet drilling. Replicate testmeasurements (10–30 measurements) lasting < 5minutes were performed on each composite material.A combination of real-time and integratedsamples were collected at the source and PBZ usingan FMPS, aerodynamic particle sizer (APS), CPC,diffusion charger, and cascade impactor to measureaerosol particle size, concentration, and chemicalidentification. An electrostatic precipitator (ESP)and thermal precipitator (TP) were used to collectparticles directly on TEM grids for electron microscopyanalysis. Aerosol concentrations duringhigh rpm drilling generally were higher than forlow rpm drilling for all composite materials withaerosol concentrations found to be higher fromalumina composites. Wet drilling was observed tosuppress the release of particles > 10 nm in diameter.High aspect-ratio fiber concentrations weredetermined using the sizing and counting criteriain NIOSH Method 7400 (> 5 µm long, aspect ratio> 3). Airborne exposure to both alumina fiber andCNT structures were found ranging in concentrationfrom 1.0 fibers/cm 3 (alumina composite) to1.9 fibers/cm 3 (carbon and CNT composite) forPBZ samples; similar concentrations were observedin area samples. Because sampling volume and fibersurface density on the samples were below theoptimal specification range of Method 7400, fiberconcentration values were determined to be firstorder approximations. The authors concluded thathigher input energies (e.g., higher drilling rpms,larger drill bits) and longer drill times associatedwith thicker composites generally produced higherexposures, and that the drilling of CNT-based compositesgenerated a higher frequency of nanofibersthan had been previously observed during the cuttingof CNT-based composites [Bello et al. 2009].Cena and Peters [2011] evaluated the airbornerelease of CNT during the weighing of bulk CNTand the sanding of epoxy nanocomposite sticksmeasuring 12.5 × 1.3 × 0.5 cm. Epoxy reinforcedtest samples were produced using MWCNT (Baytubes®)with 10–50 nm outer diameters and 1–20µm lengths. The purpose of the study was to (1)characterize airborne particles during handling ofbulk CNT and the mechanical processing of CNTcomposites, and (2) evaluate the effectiveness oflocal exhaust ventilation (LEV) hoods to captureairborne particles generated by sanding CNT composites.Airborne particle number and respirablemass concentrations were measured using a CPC(particle diameters 0.01 to 1 µm) and OPC (particlediameters 0.3 to 20 µm). Respirable mass concentrationswere estimated using the OPC data.Samples for TEM analysis were also collected forparticle and CNT characterization. PBZ and sourceairborne concentrations were determined duringtwo processes: weighing bulk CNT and sandingepoxy nanocomposite test sticks. Exposure measurementswere taken under three LEV conditions(no LEV, a custom fume hood, and a biologicalsafety cabinet). CPC and OPC particle concentrationswere measured inside a glove box in whichbulk CNT (600 mg) was transferred between two50-ml beakers; background particle concentrationswere measured inside the glove box beforethe process began. To study the sanding process, aworker manually sanded test sticks that contained2% by weight CNT. Aerosol concentrations weremeasured for 15–20 min in the worker’s breathingzone and at a site adjacent to the sanding process.The sanding process with no LEV was conductedon a 1.2 m by 2.2 m worktable. The sanding wasalso conducted inside a custom fume hood thatconsisted of a simple vented enclosure that allowedairflow along all sides of the back panel but had nofront sash or rear baffles. The average face velocityof the fume hood was 76 ft/min. Exposures fromthe sanding process were also assessed while usinga biological safety cabinet (class II type A2).Particle number concentrations determined duringthe weighing process contributed little to thatobserved in background samples (process to backgroundratio [P/B] = 1.06), however it did influencethe mass concentration (P/B = 1.79). TheGM respirable mass concentration inside the glove8 NIOSH CIB 65 • Carbon Nanotubes and Nanofibers
ox was reported as 0.03 µg/m 3 (background GM was0.02 µg/m 3 ). During the sanding process (includingno LEV, in a fume hood, and in a biological safetycabinet) the PBZ nanoparticle number concentrationswere negligible compared with backgroundconcentrations (P/B ratio = avg. 1.04). Particles generatedduring sanding were reported to be predominantlymicron sized with protruding CNT and verydifferent from bulk CNT that tended to remain inlarge (>1 µm) tangled agglomerates. Respirable massconcentrations in the worker’s breathing zone wereelevated. However, the concentrations were lowerwhen sanding was performed in the biological safetycabinet (GM = 0.2 µg/m 3 ) compared with those withno LEV (GM was 2.68 µg/m 3 ) or those when sandingwas performed inside the fume hood (GM =21.4 µg/m 3 ; p value
Page 1 and 2: CURRENT INTELLIGENCE BULLETIN 65Occ
Page 3 and 4: Current Intelligence Bulletin 65Occ
Page 5 and 6: ForewordThe Occupational Safety and
Page 7 and 8: Executive SummaryOverviewCarbon nan
Page 9 and 10: 2009; Pauluhn 2010a; Porter et al.
Page 11 and 12: neurogenic sig nals from sensory ir
Page 13 and 14: possible. Until the results from an
Page 15 and 16: ••Follow exposure and hazard as
Page 17 and 18: Periodic Evaluations••Evaluatio
Page 19 and 20: ContentsForeword ..................
Page 21 and 22: A.3.2 Comparison of Short-term and
Page 23 and 24: ESPFeFMPSFPSSgGMGSDHCLHECHEPAhrISOI
Page 25 and 26: AcknowledgementsThis Current Intell
Page 27 and 28: 1 IntroductionMany nanomaterial-bas
Page 29: 2 Potential for ExposureThe novel a
Page 32 and 33: CNMs, with MWCNT agglomerates obser
Page 36 and 37: information on air contaminants. Sa
Page 39 and 40: 3 Evidence for Potential Adverse He
Page 41 and 42: decreasing agglomerate size increas
Page 43 and 44: examined up to 60 days post-exposur
Page 45 and 46: 3.3 SWCNT and MWCNTIntraperitoneal
Page 47 and 48: The same potency sequence was obser
Page 49 and 50: Table 3-3. Findings from published
Page 55 and 56: Table 3-7 (Continued). Findings fro
Page 57: Table 3-8. Findings from published
Page 60 and 61: length, respectively) [Muller et al
Page 63 and 64: 5 CNT Risk Assessment and Recommend
Page 65 and 66: A-6). Risk estimates derived from o
Page 67 and 68: Table 5-4. Factors, assumptions, an
Page 69 and 70: and analytical methods. NIOSH is re
Page 71 and 72: Table 5-5. Recommended occupational
Page 73 and 74: deficits in animals or clinically s
Page 75: (3) Rat lung dose estimationIn the
Page 78 and 79: tasks where worker exposures exceed
Page 80 and 81: As part of the evaluation of worker
Page 82 and 83: Table 6-1. EC LODs and LOQs for 25-
Page 84 and 85:
6.2 Engineering ControlsOne of the
Page 86 and 87:
Table 6-6 (Continued). Examples of
Page 88 and 89:
Table 6-7 (Continued). Engineering
Page 90 and 91:
exposure estimates for SWCNT on ind
Page 92 and 93:
Table 6-8. Respiratory protection f
Page 94 and 95:
••Workers in areas or in jobs w
Page 97 and 98:
7 Research NeedsAdditional data and
Page 99 and 100:
ReferencesACGIH [1984]. Particle si
Page 101 and 102:
Bolton RE, Vincent HJ, Jones AD, Ad
Page 103 and 104:
eport issued on July 22, 2011. NEDO
Page 105 and 106:
Kobayashi N, Naya M, Mizuno K, Yama
Page 107 and 108:
Methner M, Hodson L, Geraci C [2010
Page 109 and 110:
Human Services, Centers for Disease
Page 111 and 112:
Piegorsch WW, Bailer AF [2005]. Qua
Page 113 and 114:
AD, Baron PA [2003]. Exposure to ca
Page 115:
Varga C, Szendi K [2010]. Carbon na
Page 119 and 120:
ContentsA.1 Introduction ..........
Page 121 and 122:
A.1 IntroductionThe increasing prod
Page 123 and 124:
provide an informal check on the es
Page 125 and 126:
these same dose groups; this effect
Page 127 and 128:
Table A-1. Rodent study information
Page 129 and 130:
the deposited (no clearance) and th
Page 131 and 132:
The other BMDS models failed to con
Page 133 and 134:
Figure A-2. Benchmark dose model (m
Page 135 and 136:
Figure A-3 (continued). Benchmark d
Page 137 and 138:
Table A-3. Benchmark dose estimates
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Table A-5. Benchmark dose estimates
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histopathology grade 2 or higher lu
Page 143 and 144:
Table A-8. Working lifetime percent
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developing early-stage adverse lung
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Figure A-4. Dose-response relations
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cell surface area). However, the wo
Page 151 and 152:
purified or unpurified (with differ
Page 153 and 154:
Table A-9. Comparison of rat or hum
Page 155 and 156:
A.6.1.3 Pulmonary Ventilation RateT
Page 157 and 158:
used as the effect levels in evalua
Page 159 and 160:
the DF estimate, although a larger
Page 161 and 162:
or overloading, of particle clearan
Page 163 and 164:
Table A-13. Human-equivalent retain
Page 165 and 166:
A.7.1 Particle CharacteristicsBoth
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and density. The following MMAD and
Page 169:
Table A-15. CNT lung dose normalize
Page 172 and 173:
B.1 Key Terms Related toMedical Sur
Page 175 and 176:
APPENDIX CNIOSH Method 5040
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filter. In the method evaluation, d
Page 179 and 180:
Most of the studies on sampling art
Page 181 and 182:
e analyzed to determine the onset o
Page 184:
Delivering on the Nation’s promis
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