nanomaterial sampling at nist
DESCRIPTION
Sampling protocols used to determine employee exposure to nanoparticles at NISTTRANSCRIPT
Applying NIOSH’s Nanomaterial Sampling Methods in the Laboratory Setting –
Preliminary Observations
Michael K. Blumer, CIHJason T. Capriotti, CIH, CSP
National Institute of Standards and Technology (NIST)Office of Safety, Health and Environment (OSHE)
Presentation Outline
Review Occupational Exposure Monitoring
Review NIOSH Sampling Methods & Limitations
Case Study: Spraying Multi-walled Carbon Nanotubes
Photo: Carbon nanotubes with impurities; Credit: NIST
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Disclaimers
Certain commercial instruments are identified in this paper in order to specify the sampling procedures adequately. Such identification is not intended to imply recommendation or endorsement by the National Institute of Standards and Technology, nor is it intended to imply that the equipment identified is necessarily the best for the purpose.
Due to the preliminary nature of the sampling activities, no attempt at deriving statistical inferences was made.
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Introduction
NIST Safety Office is evaluating exposures in working labs
NIST researchers fabricate, test, and use variety of nanomaterials
Laboratory Setting Small amounts of many different materials
Short-duration activities
Small population of highly educated, specialized workers
Exposure controls are commonly present
• Local exhaust ventilation; fume hood, etc.
• Personal protective equipment; lab coats, gloves, glasses
Ref: NIST HSI #23
Photo: Assembly of polystyrene particles held together by polyelectrolyte interaction fabricated by the Complex Fluids Group; Credit: NIST4
Occupational Exposure Monitoring
Traditional Exposure Monitoring Occupational Exposure Limit (OEL)
• Airborne concentration – mass of contaminant
• Set by governmental agency or scientific association
• Based on medical case studies, toxicology, epidemiology
Collect physical sample of airborne contaminant with pump and filter or adsorption tube
Laboratory analysis to quantify material collected
Calculate concentration and compare with OEL
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ENM Exposure Monitoring
No OELs in most cases Instead, evaluate change over background
(Standard philosophy is to control exposure to carcinogens as low as technically possible)
Chemical-specific OELs for Carbon Nanotubes and Nanowires and Titanium Dioxide Methods sensitive enough to reach lower OEL
NIOSH sampling methods for ENMs
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NIOSH NEAT Sampling Protocol
Particle Counters - Hand-held direct-reading Condensation Particle Counter (CPC)
Optical Particle Counter (OPC)
Together provide semi-quantitative estimate of nanoparticles
Filter sample for SEM/TEM analysis Particle identification and morphology
Filter sample for airborne chemical mass concentration Traditional NIOSH sampling & analytical methods
Filter pairs at nanoparticle source and researcher’s personal breathing zone (PBZ)
Ref: Methner, M. , Hodson, L. and Geraci, C. (2010) 'Nanoparticle Emission Assessment Technique (NEAT) for the Identification and Measurement of Potential Inhalation Exposure to Engineered Nanomaterials — Part A', Journal of Occupational and Environmental Hygiene, 7: 3, 127 — 132, First published on: 16 December 2009 (iFirst)
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Condensation Particle Counter
Saturated alcohol condenses on particles to grow them to 10 micrometers (µm)
Count with optical detector
10 nm – 1,000 nm particle size
1 – 100,000 (particles/cm3)
Concentration accuracy ± 20 %
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Optical Particle Counter
Counts particles based on laser light scatteringSix size channels: 300 nm – 10,000 nm
Smallest size channel = 300 nm – 500 nm
Limited data-logging memoryCounting efficiency 50 % @ 300 nm,
100 % @ >450 nmResults in particles/liter of air
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Filter Sampling
Carbon Nanotubes NIOSH Method 5040, Diesel Particulate Matter (as Elemental Carbon) Thermal-optical analysis, flame ionization detector Estimated LoD: 0.3 µg per filter portion Precision: 0.19 @ 1 µg Carbon, 0.01 @ 10 – 72 µg Carbon
SEM/TEM Analysis Filter selection: Analyst’s preference or NIOSH Method 7402, Asbestos by TEM Bulk sample to assist analyst in ENM identification Difficult with under- or over-loaded filter
Ref: National Institute for Occupational Safety and Health (NIOSH): Methods 5040 and 7402. In NIOSH Manual of Analytical Methods (NMAM), 4th ed. DHHS (NIOSH) Pub. No. 94-113. P.C. Schlecht and P.F. O’Conner (eds.) Cincinnati, Ohio: U.S. Department of Health and Human Services, Centers for Disease Control and Prevention, NIOSH, 1994.
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Case Study: Spraying Carbon Nanotubes
All work performed in fume hood, HEPA filtered exhaust to outside
Weigh dry powder
Add 20 ml water and surfactant
Sonicate solution inside enclosure and in open-top aqua sonicator
Spray liquid solution of MWCNTs by use of air brush
Apply “canned” compressed air to speed drying
Two rounds of spraying totaling 30 minutes
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Work Location
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Spraying MWCNTs
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Filter Sampling
Three pairs of filters Researcher’s personal breathing zone
Stationary samples at face of fume hood
Inside fume hood, next to target
Pump flow of 3.5 lpm for 82 minutes provides limit of quantification below REL for carbon nanotubes
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Personal Samples
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Particle Counters
CPC logs data every 1 minute
OPC logs data every 30 seconds, 1-sec. delay
Background levels before and after ENM handling
Hand-held from point of operation to PBZusually at face of hood
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Filter Sampling Results
Sample LocationSampling
Period(minutes)
Mass of elemental carbon per sample
(µg)
Concentration of elemental carbon
over sampling period
(µg/m3)
Concentration of elemental carbon as
8-hr. TWA (µg/m3)
Personal Sample;Researcher’s PBZ
1332 - 1515(103) <2 <4 <0.86
Area Sample;Inside hood
1327 - 1522(115) <2 <4 <0.96
Area Sample;Front of hood face
1333 - 1520(107) <2 <4 <0.89
NIOSH REL 8-hr TWA - -7
(as elemental carbon)
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Particle Counter Results
Three sets of data Smallest size channel on OPC (0.3 µm – 0.5 µm)
Five larger OPC size channels combined (0.5 µm – >5 µm)
CPC data (0.1 µm – >1 µm)
Four stages of work Background
Two rounds of prep combined
Two rounds of spraying combined
Cleanup
Compare geometric means, work / background
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Effect of Background Particulate Levels
13:07 13:13 13:19 13:25 13:31 13:37 13:43 13:49 13:55 14:01 14:07 14:13 14:19 14:25 14:31 14:37 14:43 14:49 14:55 15:01 15:07 15:13 15:190
2000
4000
6000
8000
10000
12000
14000
Condensation Particle Counter Measurements
Time
Parti
cles p
er cu
bic c
entim
eter
of a
ir
1
2
3
4
1
2
3
4
1
2
3
4
1
2
3
4
1
2
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4
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7
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Comparison of Work and Background Particulate Concentrations (Geometric means)
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OPC Small Size Channel
OPC Large Size Channels
CPC
OPC OPC OPC OPC0.3 - 0.5 µm 0.3 - 0.5 µm 0.3 - 0.5 µm 0.3 - 0.5 µmBackground Prep Spraying Cleanup
Geometric Mean 2227 1982 2511 2341
Work / Bkgd 0.89 1.13 1.05
OPC OPC OPC OPC0.5 - >5.0 µm 0.5 - >5.0 µm 0.5 - >5.0 µm 0.5 - >5.0 µmBackground Prep Spraying Cleanup
Geometric Mean 465 525 510 501
Work / Bkgd 1.13 1.1 1.08
CPC CPC CPC CPCBackground Prep Spraying Cleanup
Geometric Mean 3956 2847 4065 3994
Work / Bkgd 0.72 1.03 1.01
Optical Particle Counter MeasurementsSmall- and Large-Size Channels (one scale)
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Optical Particle Counter MeasurementsSmall- & Large-Size Channels (two scales)
13:5013:5413:5814:0214:0614:1014:1514:1914:2314:2714:3114:3514:3914:4414:4814:5214:5615:0015:0415:0815:1215:170
500
1000
1500
2000
2500
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3500
4000
0
100
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Small particlesLarge Particles
Time
Smal
l Par
ticle
s per
lite
r of a
ir
Larg
e Pa
rticle
s per
lite
r of a
ir
Prep Spraying Prep Spraying Clean
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13:5013:5413:5814:0214:0614:1014:1514:1914:2314:2714:3114:3514:3914:4414:4814:5214:5615:0015:0415:0815:1215:170
500
1000
1500
2000
2500
3000
3500
4000
0
100
200
300
400
500
600
700
800
Optical Particle Counter Measurements
Small particlesLarge Particles
Time
Smal
l Par
ticle
s per
lite
r of a
ir
Larg
e Pa
rticle
s per
lite
r of a
ir
Prep Spraying Prep Spraying Clean
13:5013:53
13:5613:59
14:0214:05
14:0814:11
14:1414:17
14:2014:23
14:2614:29
14:3214:35
14:3814:41
14:4414:47
14:5014:53
14:5614:59
15:0215:05
15:0815:11
15:1415:17
0
1000
2000
3000
4000
5000
6000
Condensation Particle Counter Measurements
Time
Parti
cles p
er cu
bic c
entim
eter
of a
ir
Prep Spraying Prep Spraying Clean
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Conclusions
Researcher was not exposed to measureable levels of airborne MWCNTs during spraying
Local exhaust ventilation with HEPA filtration is effective at controlling nanoparticles
Limitations of particle counters significantly hamper identification of nanoparticles
Difficult to identify ENMs over normal background
Can improve sensitivity by activelylowering background particleconcentration- Do not need to HEPA filter incoming air
Photo: Nanowires that emit UV lightCredit: Lorelle Mansfield/NIST
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Questions?
Photo: A 40-nanometer-wide NIST logo made with cobalt atoms on a copper surface. The ripples in the background are made by electrons, which create a fluid-like layer at the copper surface. Each atom on the surface acts like a pebble dropped in a pond. Credit: J. Stroscio, R. Celotta/NIST
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