Occupational Exposure to Carbon Nanotubes and Nanofibers

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Table 6–1. EC LODs and LOQs for 25- and 37-mm filters (ug EC/cm 2 )25-mm filter EC (n = 10) 37-mm filter EC (n = 6)Mean 0.063 Mean 0.033Standard deviation 0.030 Standard deviation 0.028LOD 0.09 LOD 0.08LOQ 0.30 LOQ 0.28Table 6–2. OC LODs and LOQs for 25- and 37-mm filters (ug OC/cm 2 )25-mm filter OC (n = 10) 37-mm filter OC (n = 6)Mean 1.41 Mean 1.94Standard deviation 0.413 Standard deviation 0.281LOD 1.24 LOD 0.84LOQ 4.13 LOQ 2.81Table 6–3. OC, EC, and TC LODs and LOQs for 37-mm filters (ug C/cm 2 )37-mm filter OC EC OC EC TCMean 1.31 0.03 1.44 0.03 1.52Standard deviation 0.164 0.016 0.304 0.024 0.318LOD 0.49 0.05 0.91 0.07 0.95LOQ 1.64 0.16 3.04 0.24 3.18As stated on previous page, NIOSH Method 5040LOD depends on the air volume, filter size, sampleportion analyzed (usually 1.5 cm 2 ), and the mediablank variability. The latter is used to determine theLOD in unit’s µg/cm 2 . Expressed as an air concentration,the EC LOD (µg/m 3 ) corresponding to theEC LOD (µg/cm 2 ) determined with media blanks(i.e., LOD = 3 times the standard deviation for theblanks) can be calculated by the following equation:This equation explains why a lower LOD (µg/m 3 )can be obtained by reducing the filter size (depositarea), increasing the air volume, and minimizingthe variability for the media blanks (i.e., the ECLOD in µg/cm 2 ). The LOD is improved using asmaller filter size since the deposit density is higherfor an equivalent mass deposited. The same appliesto the LOQ, commonly defined as 10 timesthe standard deviation (SD) for the blanks, or 3.3times the LOD.If 0.02 µg EC/cm 2 is taken as the SD for mediablanks (with manual OC-EC split adjustment),the LODs and LOQs (in µg EC/m 3 ) for different56 NIOSH CIB 65 • Carbon Nanotubes and Nanofibers
air volumes, 25-mm and 37-mm filters, and a1.5 cm 2 filter portion analyzed would be as listedin Table 6–4. Results for a SD double this value(i.e., SD = 0.04 µg EC/cm 2 ) also are reported asworst-case estimates, but are seldom this high. IfSDs for media blanks are frequently above 0.02ug EC/cm 2 ) the cause of the high blank variabilityshould be identified and corrected.Based on EC results for media blanks (Tables 6–1and 6–3), a filter loading of about 0.3 µg/cm 2 (i.e.,at or above the EC LOQs reported in Tables 6–1and 6–3) will provide quantitative results.As described above (6.1.2), higher flow rate respirablesamplers (cyclones) with a 25 mm cassettecan improve the sample collection to permitmeasurement of CNT and CNF above the LOQ(i.e., 1 µg/m 3 ) for samples collected for less thanfull work shift. Examples of sampling periods andflow rates that provide air volumes of about a halfcubicmeter or higher (shaded area in table below)are listed in Table 6–5. A larger filter portion alsocan be used to further lower the LOD, but the instrument’ssmall (quartz tube) oven and need forproper sample alignment limit the amount of samplethat can be analyzed.Table 6–4. EC LODs and LOQs estimated with media blanksEC LOD and LOQ (µg EC/m 2 )3 m 3 air 1 m 3 air 0.5 m 3 airSD blank(µg EC/cm 2 )LimitEC limit(µg/cm 2 )37-mmfilter25-mmfilter37-mmfilter25-mmfilter37-mmfilter25-mmfilter0.02 LOD 0.06 0.17 0.07 0.51 0.21 1.02 0.42LOQ 0.20 0.57 0.23 1.70 0.69 3.40 1.380.04 LOD 0.12 0.34 0.14 1.02 0.42 2.04 0.83LOQ 0.40 1.13 0.46 3.40 1.38 6.80 2.77Table 6–5. Examples of sampling periods and flow ratesAir volumes (m 3 ) for indicated sampling periods (hours) and flow ratesFlow rate (lpm) † 1 h ‡ 2 h 4 h 8 h2 120 240 480 9604 240 480 960 19206 360 720 1440 28807 420 840 1680 3360†Liters per minute (lpm).‡Sampling period, hours, and highest flow rate tested at NIOSH laboratory. Tested with a Leland Legacy pump and 25-mmquartz-fiber filter.NIOSH CIB 65 • Carbon Nanotubes and Nanofibers57
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CURRENT INTELLIGENCE BULLETIN 65Occ
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Current Intelligence Bulletin 65Occ
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ForewordThe Occupational Safety and
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Executive SummaryOverviewCarbon nan
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2009; Pauluhn 2010a; Porter et al.
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neurogenic sig nals from sensory ir
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possible. Until the results from an
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••Follow exposure and hazard as
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Periodic Evaluations••Evaluatio
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ContentsForeword ..................
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A.3.2 Comparison of Short-term and
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ESPFeFMPSFPSSgGMGSDHCLHECHEPAhrISOI
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AcknowledgementsThis Current Intell
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1 IntroductionMany nanomaterial-bas
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2 Potential for ExposureThe novel a
Page 32 and 33: CNMs, with MWCNT agglomerates obser
Page 34 and 35: composite materials with local exha
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 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
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Figure A-2. Benchmark dose model (m
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Figure A-3 (continued). Benchmark d
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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
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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
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purified or unpurified (with differ
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Table A-9. Comparison of rat or hum
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A.6.1.3 Pulmonary Ventilation RateT
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used as the effect levels in evalua
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the DF estimate, although a larger
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or overloading, of particle clearan
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Table A-13. Human-equivalent retain
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A.7.1 Particle CharacteristicsBoth
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and density. The following MMAD and
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Table A-15. CNT lung dose normalize
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B.1 Key Terms Related toMedical Sur
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APPENDIX CNIOSH Method 5040
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filter. In the method evaluation, d
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Most of the studies on sampling art
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e analyzed to determine the onset o
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Delivering on the Nation’s promis
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