Woodrow Wilson Center, Project on Emerging Nanotechnologies
Andrew D. MaynardChief Science Advisor
Engineered NanomaterialsMeasurement in the occupational
setting
ECETOC. Nanomaterials. Barcelona, Nov 7 - 9 2005
Woodrow Wilson Center, Project on Emerging Nanotechnologies 2
Compositional Structure
Ph
ysic
al
Str
uctu
re
Influence of structure on potential health impact
Potential Health ImpactWhat makes ‘nano’ different?
Lo
wH
igh
Gases & Vapors
Liquids
Macro-Materials
Nano-Materials & Devices
Low High
Conventional Understanding
Unconventional Understanding
Mass
Composition
Surface Area
Nano-Structure
Surface Activity
Size
Shape
Woodrow Wilson Center, Project on Emerging Nanotechnologies 3
Engineered Nanomaterials - Structure is ImportantExample: Zinc Oxide nanostructures
Materials Today June 2004. Zhong Lin Wang, Georgia Institute of Technology
Woodrow Wilson Center, Project on Emerging Nanotechnologies
Nanoparticles
Simple, complex, “smart”.
Aerosols, powders,
suspensions, slurries
Agglomerates
or aggregates of
nanoparticles
Comminution
Aerosols from grinding,
cutting, machining
nanomaterials
Aerosolized suspensions
Including slurries and
solutions of nanomaterials
Degredation/Failure
Aerosols and suspensions
resulting from degradation
and failure of nanomaterials
Unintentional use
Potential exposure from
unanticipated/unintentional
use?
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Setting BoundariesEngineered nanomaterials which potentially present new challenges
! Criteria:
• Nanomaterials capable of entering or interacting with the body
• Nanomaterials which potentially exhibit nanostructure-dependent
biological activity
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Particle CategoriesClasses of engineered nanoparticles
A. Spherical
homogeneous
B. Fibrous
homogeneous
C. Non-spherical
homogeneous
D. Agglomerate
homogeneous
E. Heterogeneous
concentric
F. Heterogeneous
distributed
G. Heterogeneous
agglomerate
H. Active
particle
I. Multifunctional
particle
(not necessarily inclusive)Aitken and Maynard, in preparation
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Measuring exposureAttribute + related physical quantity " exposure metrics
Attribute Particle Type
A B C D E F G H I
Size / size distribution
Shape
Chemical Composition
Surface Chemistry
Size dependent properties
Morphology dependent properties
Physicochemical structure-dependent properties
Solubility
Charge (in lung fluid)
Crystallinity
Physicochemical structure
Inter-particle adhesive forces
Physical re-structuring potential
Size distribution
Temporal changes in physicochemical structure
Component particle dissociation (in body)
Differential component dissociation (in body)
Synergistic interactions
Stimulus-associated behavior
Functional response to environment
Mass
Surface Area
Number
Associated metrics
(Indicative only)
Aitken and Maynard, in preparation
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Mass
Woodrow Wilson Center, Project on Emerging Nanotechnologies 8
Mass-based Exposure Measurement
! Relevance
• Provides continuity with historic measurements/methods
• Over 50 years experience in measuring mass concentration
• When is mass concentration relevant to the health implications of
exposure to nanomaterials?
! Conversions
• Can mass concentration measurements be converted to other
metrics?
• Possible, but additional information is needed (such as aerosol size
distribution)
• Conversions are heavily biased by larger particles
! Sensitivity
• Is the limit of quantification of mass-based methods sufficient for
nanomaterials?
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Gravimetric analysis - sensitivity
Example.
! Conventional material: 5 mg/m3 OEL
! Nanomaterial:
• Particles are 100 times smaller
• Surface area is 100 times larger
• Possible nano-OEL is 100 times lower - 50 !g/m3
! Gravimetric analysis
• Limit Of Quantification between 5 - 50 !g [est].
• 8 hour sample at 2 l/min: 48 !g collected at nano-OEL
• Just within LOQ - with a good balance system
! Problems if the conventional OEL is significantly lower than
5 mg/m3.
! Chemical speciation is an option
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Number
Woodrow Wilson Center, Project on Emerging Nanotechnologies 11
3007 Portable CPC, www.tsi.com
Number-based Exposure Measurement
! Portable Condensation Particle
Counter
• Responds to particles larger than
~10 nm
• Very sensitive to low
concentrations. Limited at high
concentrations (105 particles/cm3
for the TSI 3007)
• Background counts: can be as
high as 106 particles/cm3 and
above
• Not material-specific
• Good for ‘sniffing out’ sources
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Surface Area
Woodrow Wilson Center, Project on Emerging Nanotechnologies 13
Aerosol Surface-Area MeasurementEstablished Method - BET
! Limitations:
• Needs substantial quantity
of material
• Does collection modify
surface area?
• Porosity
• Delayed feedback
• Expensive and time
consuming
Detector
Adsorption
Desorption
Brunaeur, Emmett and Teller , J. Amer. Chem Soc. 60, 309 (1938)
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TEM Image
Aerosol Surface-Area MeasurementTransmission Electron Microscope Analysis
Isolated particle
Measure the
projected area
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Aerosol surface
area per m3
1000
105
107
109
1011
1013
10 100 1000 104
Ceramic
Granite
Steel
Aluminum
PTFE
hardwood
dn/d
Log(d
) / part
icle
s m
-3
Equivalent sphere projected-area diameter / nm
Number Distribution
10-7
10-6
10-5
0.0001
0.001
0.01
0.1
10 100 1000 104
CeramicGraniteSteelAluminumPTFEHardwood
ds/d
Log(d
) / m
2 m
-3
Equivalent sphere projected-area diameter / nm
Surface Distribution
Zimmer, A. T. and Maynard, A. D. Ann. Occup. Hyg. 46 (8), 663-672, 2002.
Aerosol Surface-Area MeasurementDerived from size distribution measurements
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Aerosol surface-area measurementUsing attachment rate
++
Ions
Electrometer
Charge on
Aerosol
Surface
Area!
DC2000 CE Diffusion Charger
EcoChem
++
+
+
+
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Monodisperse Test Particles
Generation
(Silver Particles)
Selection
Increasing sintering temperature
Generatingf urnace
Sintering
f urnaceDMACoagulation
chamber
MFC
Optional
HPEA
Pure
N2
Carrier
gasFractal-like
particles
Spherical
particles
Ku, B. K. and Maynard, A. D. J. Aerosol Sci. 36 (9), 1108-1124, 2005.
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Comparison of measurement methodsMonodisperse particles < 100 nm, fractal-like
0
2000
4000
6000
8000
0 1000 2000 3000 4000 5000 6000 7000 8000
Me
as
ure
d p
roje
cte
d a
rea
pe
r p
art
icle
(n
m2)
Actual projected area per particle (nm2)
1:1
Scanning Mobility Particle Sizer
Transmission Electron Microscope
Diffusion Charger (benchtop)
Diffusion charger (portable)
20 nm
100 nm
Ku, B. K. and Maynard, A. D. J. Aerosol Sci. 36 (9), 1108-1124, 2005.
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Aerosol surface-area measurementDiffusion Charger Response
100
1000
104
105
20 40 60 80 100
Diffu
sio
n C
ha
rge
r R
esp
on
se
(Me
an
pa
rtic
le p
roje
cte
d s
urf
ace
are
a,
nm
2)
d (nm)
y = 0.64023 * x^(2.0611) R2= 0.92827
y = 7.1218 * x^(1.5277) R2= 0.95767
Ku, B. K. and Maynard, A. D. J. Aerosol Sci. 36 (9), 1108-1124, 2005.
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0
0.2
0.4
0.6
0.8
1
10 100 1000 104
Particle diameter / nm
Size Distribution (Surface)
Alveolar deposition
Emerging Measurement TechnologiesSurface Area
Diffusion Charger
www.ecochem.biz
Deposited Surface Area
Nanoparticle Surface Area Monitor
www.tsi.com
W ilson, W . E., in Proceedings of the 2004 Air and W aste Management Association Conference, 2004.
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Future Requirements
A
BSurface
C
A
C
BMass
C
BNumber
A
Me
tric
Low
Cost
Chem
ical
specific
ity
Sim
plic
ity
of o
pera
tion
Bre
ath
ing
zone
Porta
bility
Tem
pora
l
Resolu
tion
Measurement Method attributes
< 100 !m
< 4 !m
< 100 nm
Research
Prioriti
es?
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Emerging Measurement Technologies
! Deposited Surface Area Measurement
• Surface area weighted by deposition probability
• Fissan, Wilson, TSI Inc. et al.
! Micro-Electro Mechanical Systems (MEMS)
• Personal size distribution measurements
• Chen et al.
! Simple geometry electrostatic separation
• Simple compact measurement instruments
• Dhaniyala et al.
! Opposed Migration Aerosol Classifier
• Inexpensive/compact size distribution measurements
• Flagan et al.
! Common theme: using aerosol electrical properties
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Summary
! Simplification
• Airborne engineered nanomaterials are complex: Monitoring
requirements need to be simplified if viable exposure measurement
methods are to be developed
! Number, surface area and mass are important
• Although aerosol surface area is clearly important, number and mass
concentration remain relevant exposure metrics
! Further development is needed
• While measurement methods for number, surface area and mass
concentration are available, further research and development is
needed to develop simple, cost-effective and relevant exposure
monitors
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Contact Information
Dr Andrew D. MaynardChief Science Advisor
Project on Emerging NanotechnologiesWoodrow Wilson International Center for Scholars at the Smithsonian Institute
One Woodrow Wilson Plaza
1300 Pennsylvania Ave. NW
Washington DC 20004
Tel: 202 691 4311
Email: [email protected]
URL: www.wilsoncenter.org
