Transcript CMLong - Society for Risk Analysis

Exposure Assessment of
Engineered Nanoparticles:
Challenges, Progress,
Opportunities
Christopher Long, Sc.D.
November 19, 2008
SRA-NE Seminar
Overview
• Key Questions:
– How, What or Who, When, Where, How Much?
– What data are currently available to evaluate NP
exposure potential?
– Are existing Best Management Practices for
dusts, fumes, and mists effective for engineered
NPs?
– What are some key challenges and data gaps
for understanding potential exposures to
nanoparticles?
Motivation
Risk = function (Hazard, Exposure)
Meaning that:
With little or no exposure, there can be no
significant health risks.
Nanotechnology is “Now”
Photo by David Hawxhurst, Woodrow Wilson Center
Over 800 consumer products worldwide …
Not Everything “Nano” is Actually
Nano
Nano-sized Particles Are Not Novel
Natural NPs
• Ambient air chemistry
(e.g., gas-to-particle
conversions)
• Forest fires
• Volcanoes
• Viruses
• Biogenic magnetite
• Proteins
Anthropogenic Incidental NPs
• Internal combustion engines
• Fossil fuel power plants
• Incinerators
• Jet engines
• Metal fumes (smelting, welding)
• Polymer and other fumes
• Cooking (frying, broiling,
grilling, baking, toasting)
• Heated surfaces
• Electric motors (vacuum
cleaners)
• Office equipment
• Candles
Nano-sized Particles Are Ubiquitous!
500
400
Number Conc.
dN/dlog(dp)
Mopping with
Pine Sol
300
Frying egg;
toasting bagel
(#/cm3)
1e+2
5e+2
1e+3
3e+3
5e+3
8e+3
1e+4
3e+4
5e+4
8e+4
1e+5
3e+5
Particle Diameter (nm)
200
Popping popcorn
with air popper
100
90
80
70
60
50
40
30
20
6
8
10
12
14
7/10/98
16
18
20
Hour of Day (EST)
22
0
2
7/11/98
4
What’s Published About NP
Exposure Potential?
1000
Toxicology Subset of Nano Studies in PubMed
Handcount of Exposure Studies in PubMed/ICON
Virtual Journal- Only Studies of Engineered NPs
Exposure Studies per ICON Nano-EHS Database
Analysis Tool
# of Publications
800
600
400
200
0
2000
2001
2002
2003
2004
Year
2005
2006
2007
2008
How NP Exposure May Occur
Potential Human Exposure Routes and
Pathways
• Potential for inhalation, dermal contact, and
ingestion exposures
• Workplace settings recognized
to have greatest exposure potential
• But general population exposures
cannot be overlooked
– Direct exposures from use of consumer products
– Indirect exposures to NPs in the environment from
releases resulting from production, use, and end-oflife (e.g., landfilling, incineration, recycling)
NP Sources and Potential Routes to
the Environment
Probable Exposure Routes
Sector/Application
Nanomaterial
Air
Cosmetics and personalcare products
TiO2, ZnO, fullerene
(C60), Fe2O3, Ag
Catalysts, lubricants and
fuel additives
CeO2, Pt, MoS3
Paints and coatings
TiO2, SiO2, Ag,
quantum dots
Water treatment and site
remediation
Fe, Fe-Pd,
polyurethane
Agrochemicals
SiO2 (porous) as a
carrier
Food packaging
Ag, nanoclay, TiO2
Pharmaceuticals and
medicines
Nanomedicines and
carriers
(Adapted from Boxall et al., 2007)
Surface
Water
Ground
Water
Wastewater
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Soil
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Quantifying NP Exposure: What’s the
Relevant Exposure Metric?
Schwartz et al. (2002)
Stolzel et al. (2007)
Monteiller et al. (2006)
“Each One May
Be Right”
Many Different Shapes,
Chemistries, etc.
N. Walker, National Toxicology Program
Expanded List of Possible
Measures of NP Exposure
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Mass concentration
Surface area
Number concentration
Surface reactivity
State of
Agglomeration
• Weighted size
distribution
• Morphology (Shape)
• Surface charge
• Chemical composition
Measuring Exposure
• Mass, Number, Surface Area?
TSI 3550 Nanoparticle
Surface Area Monitor
TSI 3007
Portable CPC
MSP Corp.
NanoMOUDI-II
EcoChem
DC2000 CE
Diffusion
Charger
TEM/SEM
Particle Size Measurement
MSP Corp.
Wide-Range Particle
Spectrometer
Dekati Electrical
Low Pressure
Impactor (ELPI)
Met One
HHPC-6
Optical Particle Counter
TSI 3034
SMPS
MSP Corp.
NanoMOUDI-II
Lack of Specificity
• Process-related or other nanoparticles?
– Need for careful data interpretation and/or more specific
detection methods (e.g., shape recognition, elemental analysis)
From Kuhlbusch et al. (2001)
Potential Exposures During Simulated CNT
Handling Scenarios
• Evidence for
agglomeration
under realistic
handling
processes; low
respirable CNT
concentrations
Adapted from Maynard et al. (2004), Maynard (2005)
Airborne PM in a Fullerene Factory
• During removal of fullerenes
from storage tank for bagging
and/or weighing, no elevation
in Dp<50 nm, but elevation for
Dp>1,000 nm
• SEM confirmed emission of
fullerene aggregates/
agglomerates
• Consistent with findings from
Maynard et al. (2004),
observed increase in particle
number conc. at Dp<50 nm
during vacuuming
(Fujitani et al., 2008)
Airborne Metal Oxide NPs at an Industrial
Pilot Plant
• Results indicate high
temperature gas-phase
production unit to be main
particle source
– Average conc. of 59,100 cm-3
and 188 mg/m3
– Direct reactor leaks?
• Vacuum cleaner increased
number conc. but not mass
conc.
• No substantial rise in
submicron particles during
particle handling and
processing
(Demou et al., 2008)
Airborne Exposures During NP Handling
in Fume Hoods
• Pilot study demonstrates NP
exposures when handling dry
powders in standard fume hoods
Pouring of 100 g Nanoalumina NPs
– Potential for NP releases:
Conventional>by pass>constant velocity
– Highly dependent on many variablese.g., hood design, hood operation, work
practices, type and quantity of NPs, etc.
• Released NPs remained airborne in
laboratory air for up to 2 hours
• Well-designed hoods, operated at a
constant face velocity (e.g., constant
velocity hoods), shown to be
protective under all test conditions
(Tsai et al., 2008)
NIOSH Field Investigations
• Since 2006, NIOSH field team has conducted ~20 site
visits
– Variety of workplaces- e.g., commercial R&D labs, university labs,
manufacturing facilities
– Variety of NP types- e.g., carbon nanofibers, metal oxides, QDs
• Development of Nanoparticle Emission Assessment
Technique (NEAT)
– Baseline assessment utilizing portable instruments (CPC and
HHPC-6) for particle number measurements
• Are particle number concentrations “higher” with production system
on?
• ~25% increase above background used as subjective decision point
• If Yes, filter-based samples for TEM and chemical analysis collected
– Expanded assessment using less portable, more expensive
particle analyzers (e.g., SMPS, surface area analyzers)
Preliminary NIOSH Results
• Available data show measurable particle
releases (but generally not NPs!)
– Release of >400 nm particles during weighing/
mixing of carbon nanofibers and wet-sawing of
composite materials (Methner et al., 2007)
– Effectiveness of Local Exhaust Ventilation (LEV)
during reactor cleanout operations (Methner, 2008)
Exposure to Free NPs from
Consumer Products???
• Few available data for
realistic consumer
product use scenarios
– For sunscreens, studies show
no significant penetration of
TiO2 or ZnO NPs.
– For products such as
nanocomposite sporting
goods, low exposure potential
expected due to incorporation
into solid, impermeable
matrices.
– Limited data suggest releases
possible during product
modification (e.g., sanding,
sawing).
PNNL Sanding Study of CNT
Nanocomposites
Categorization Framework for Consumer
Products (Hansen et al., 2008)
• Based on location of nanostructure in product
• Three broad exposure categories
– Expected to cause exposure: “nanoparticles suspended in liquids” and
“airborne nanoparticles”
– May cause exposure: “surface-bound nanoparticles”
– No exposure expected to consumer: “nanoparticles suspended in
solids”
• Applied to Woodrow Wilson Consumer Products Inventory
– Categorized 45% of products into the “likely exposure” category, 9% into
the category of “no likely exposure,” and 25% as unclassifiable
– Highest exposure potential for products in the categories food/
beverages and health/fitness
– Highest exposure potential for Ag, TiO2, and ZnO
– Several limitations, including lack of information about location of
nanomaterials in many products
Effectiveness of Traditional Filter Media
(Pui et al., 2008)
Conclusions
• Measurable NP emissions can be released during typical
manufacturing and handling processes
– Only moderate increases in NP conc. compared to background
levels- i.e., uncertain relevance to human health
• Critical need for additional data representative of realworld exposure conditions
– Need for not only more workplace studies, but also studies to
determine the likelihood and conditions for potential releases of
free NPs from consumer products and end-of-life processes
• Growing evidence that traditional exposure controls can
effectively reduce NP exposure levels
– Research indicates that not all fume hoods may be protective
Exposure Assessment Needs
• Field measurements of actual workplace
conditions
– Need to establish the relationship between basic
measurements and research-grade measurements
– Need to establish the relevant exposure metric(s)
• Personal universal aerosol monitor that meets
criteria for price, ease of use, and size
• Real-time instrumentation that can discriminate
nano-sized particles of interest
• Standardized methods and reference materials
for assessment of particle size, size distribution,
shape, structure, and surface area
Any Questions?
[email protected]
(617) 395-5532