Occupational Exposure to Carbon Nanotubes and Nanofibers

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the thermal-optical instrument was available inonly one laboratory. After additional laboratoriesacquired thermal-optical instruments, a roundrobin comparison [Birch 1998] was conducted.Matched sets of filter samples containing differenttypes of complex carbonaceous aerosols were distributedto 11 laboratories. Six of the eleven analyzedthe samples according to NIOSH 5040, whilefive used purely thermal (i.e., no char correction)methods. Good interlaboratory agreement was obtainedamong the six laboratories that used NIOSH5040. In the analysis of samples containing DPM,the variability (RSD) for the EC results rangedfrom 6% to 9%. Only low EC fractions were foundin wood and cigarette smoke. Thus, these materialspose minimal interference in the analysis of EC. Inaddition, only minor amounts of EC were found intwo OC standards that char: about 1% for sucroseand 0.1% for the disodium salt of ethylene diaminetetraaceticacid (EDTA). Two aqueous solutionsof OC standards were included in the comparisonas a check on the validity of the char correction andaccuracy of the TC results. Variability (RSD) of theTC results for the two standard solutions and fivefilter samples ranged from 3% to 6%.A second interlaboratory comparison study usingNIOSH 5040 was also conducted [Schauer et al.2003]. Seven environmental aerosol samples wereanalyzed in duplicate by eight laboratories. Foursamples were collected in U.S. cities, and three werecollected in Asia. Interlaboratory variability for theEC results ranged from 6% to 21% for six sampleshaving EC loadings from 0.7 to 8.4 µg/cm 2 . Four ofthe six had low EC loadings (0.7 µg/cm 2 to 1.4 µg/cm 2 ). The variability for the OC results ranged from4% to 13% (OC loadings ranged from about 1 to25 µg/cm 2 ). Results for TC were not reported, butthe variability reported for the OC results shouldbe representative of that for TC, because the sampleswere mostly OC (75% to 92%). Similar findingswere also reported by Chai et al. [2012] fromseven laboratories in which analysis was performedusing Method 5040 on four sample filter sets containingOC and EC. The summary RSDs for EC resultswere
Most of the studies on sampling artifacts apply toenvironmental air sampling. Occupational samplingmethods and conditions are generally much differentthan environmental. Environmental samplesare usually collected at much higher face velocities:20–80 cm/s as opposed to 3–4 cm/s for occupationalsamples. In addition, the concentrations of carbonare much lower in environmental air than in mostoccupational settings [Fruin et al. 2004; Sheesleyet al. 2008], and the types of aerosols sampled aredifferent (e.g., aged aerosol from multiple environmentalsources, as opposed to aerosols close tosource). These differences are important becauseOC sampling artifacts depend upon conditionssuch as filter face velocity, air contaminants present,sampling time, and filter media. Given themuch lower filter face velocities typical of occupationalsampling, adsorption (i.e., positive artifact)is expected over evaporation for occupational samples.Turpin et al. [1994], Kirchstetter et al. [2001],Noll and Birch [2008], and Schauer et al. [1999]have reported adsorption as the dominant artifact.To correct for the positive adsorption artifact, tandemquartz filters have been applied. When samplingwith tandem filters, particulate matter iscollected by the first filter, while both the first andsecond filters are exposed to and adsorb gaseousand vaporous OC. For the correction to be effective,both filters must be in equilibrium with thesampled airstream, adsorb the same amount of gas/vapor OC, and not have a significant amount of OCloss through evaporation. The OC on the secondfilter can then be subtracted from the OC on thefirst filter to account for the adsorbed OC. Severalstudies have found the tandem filter correction tounderestimate the adsorption artifact [Turpin et al.2000; McDow and Huntzicker 1990; Turpin et al.1994; Olson and Norris 2005], while others haveshown effective correction [Kirchstetter et al. 2001;Mader et al. 2003; Subramanian et al. 2004; Maderet al. 2001; Noll and Birch 2008].Air samplers containing a Teflon® and quartz filteralso have been used for correction of the positiveOC artifact. In theory, the Teflon top filter collectsparticulate matter with negligible OC gas/vaporadsorption, so only the quartz filter beneath it adsorbsgas and vapor OC. Studies on tandem filtercorrections have shown the quartz filter beneathTeflon to have a greater OC value than quartz beneathquartz [Turpin et al. 2000; Olson and Norris2005]. This finding was attributed to the quartzbeneath quartz not reaching equilibrium with thesampling stream and underestimating the adsorptionartifact. Others have attributed it to the evaporationartifact being more prevalent when using aTeflon filter instead of a quartz filter, and they reportedthe quartz behind Teflon to overestimatethe adsorption artifact [Subramanian et al. 2004].Several studies have shown no difference when usingeither type of correction [Mader et al. 2003;Mader et al. 2001].Noll and Birch [2008] conducted studies on OCsampling artifacts for occupational samples to testthe accuracy of the tandem quartz-filter correction.In practice, using two quartz filters for air samplingis preferable to the Teflon-quartz combination becauseboth the collection and blank filters are inthe same sampler. The tandem quartz correctioneffectively reduced positive bias for both laboratoryand field samples. Laboratory samples werecollected under conditions that simulated DPMsampling in underground mines. Without correction,TC on the sample filter was 30% higher thanthe actual particulate TC for 50% of the samples,but it was within 11% of the particulate TC after thetandem quartz-fiber correction. For field samples,this correction significantly reduced positive biasdue to OC adsorption artifact. Little artifact effectwas found after the correction was made.C.6 Carbon Nanotubesand NanofibersMethod 5040 was developed to measure DPM inoccupational environments, but it can be appliedto other types of carbonaceous aerosols. When appliedto materials such as carbon black or CNT/CNF, particle deposition on a filter may be morevariable because particles in these materials aremuch larger than DPM. Variability depends on theNIOSH CIB 65 • Carbon Nanotubes and Nanofibers153
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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
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CNMs, with MWCNT agglomerates obser
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composite materials with local exha
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information on air contaminants. Sa
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3 Evidence for Potential Adverse He
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decreasing agglomerate size increas
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examined up to 60 days post-exposur
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3.3 SWCNT and MWCNTIntraperitoneal
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The same potency sequence was obser
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Table 3-3. Findings from published
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Table 3-7 (Continued). Findings fro
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length, respectively) [Muller et al
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5 CNT Risk Assessment and Recommend
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A-6). Risk estimates derived from o
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Table 5-4. Factors, assumptions, an
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and analytical methods. NIOSH is re
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Table 5-5. Recommended occupational
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deficits in animals or clinically s
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(3) Rat lung dose estimationIn the
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tasks where worker exposures exceed
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As part of the evaluation of worker
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Table 6-1. EC LODs and LOQs for 25-
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6.2 Engineering ControlsOne of the
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Table 6-6 (Continued). Examples of
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Table 6-7 (Continued). Engineering
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exposure estimates for SWCNT on ind
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Table 6-8. Respiratory protection f
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••Workers in areas or in jobs w
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7 Research NeedsAdditional data and
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ReferencesACGIH [1984]. Particle si
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Bolton RE, Vincent HJ, Jones AD, Ad
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eport issued on July 22, 2011. NEDO
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Kobayashi N, Naya M, Mizuno K, Yama
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Methner M, Hodson L, Geraci C [2010
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Human Services, Centers for Disease
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Piegorsch WW, Bailer AF [2005]. Qua
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AD, Baron PA [2003]. Exposure to ca
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Varga C, Szendi K [2010]. Carbon na
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ContentsA.1 Introduction ..........
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A.1 IntroductionThe increasing prod
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provide an informal check on the es
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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
Page 139 and 140: Table A-5. Benchmark dose estimates
Page 141 and 142: histopathology grade 2 or higher lu
Page 143 and 144: Table A-8. Working lifetime percent
Page 145 and 146: developing early-stage adverse lung
Page 147 and 148: Figure A-4. Dose-response relations
Page 149 and 150: 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
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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
Page 167 and 168: 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
Page 177: filter. In the method evaluation, d
Page 181 and 182: e analyzed to determine the onset o
Page 184: Delivering on the Nation’s promis
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