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

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Condensation Particle Counter Measurements

Time

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cles p

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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

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Small particlesLarge Particles

Time

Smal

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ticle

s per

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r of a

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Larg

e Pa

rticle

s per

lite

r of a

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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

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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

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14:4414:47

14:5014:53

14:5614:59

15:0215:05

15:0815:11

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Condensation Particle Counter Measurements

Time

Parti

cles p

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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?

michael.blumer@nist.gov

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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