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Exposure Assessment of Engineered Nanoparticles:
Challenges, Progress, Opportunities
Christopher Long, Sc.D.November 19, 2008SRA-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”
Over 800 consumer products worldwide …Photo by David Hawxhurst, Woodrow Wilson Center
Not Everything “Nano” is Actually Nano
Nano-sized Particles Are Not NovelNatural 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!
Hour of Day (EST)
6 8 10 12 14 16 18 20 22 0 2 4
Pa
rtic
le D
iam
ete
r (n
m)
20
30
40
50
60
70
80
90
200
300
400
500
100
1e+2 5e+2 1e+3 3e+3 5e+3 8e+3 1e+4 3e+4 5e+4 8e+4 1e+5 3e+5
Number Conc.dN/dlog(dp)
(#/cm3)
7/10/98 7/11/98
Frying egg;toasting bagel
Mopping withPine Sol
Popping popcornwith air popper
Year
2000 2001 2002 2003 2004 2005 2006 2007 2008
# of
Pub
licat
ions
0
200
400
600
800
1000
Toxicology Subset of Nano Studies in PubMedHandcount of Exposure Studies in PubMed/ICON Virtual Journal- Only Studies of Engineered NPsExposure Studies per ICON Nano-EHS Database Analysis Tool
What’s Published About NP Exposure Potential?
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-of-life (e.g., landfilling, incineration, recycling)
NP Sources and Potential Routes to the Environment
Sector/Application
Nanomaterial
Probable Exposure Routes
AirSurface Water
Ground Water
Wastewater Soil
Cosmetics and personal-care products
TiO2, ZnO, fullerene
(C60), Fe2O3, Ag
Catalysts, lubricants and fuel additives
CeO2, Pt, MoS3
Paints and coatingsTiO2, SiO2, Ag,
quantum dots
Water treatment and site remediation
Fe, Fe-Pd, polyurethane
AgrochemicalsSiO2 (porous) as a
carrier
Food packaging Ag, nanoclay, TiO2
Pharmaceuticals and medicines
Nanomedicines and carriers
(Adapted from Boxall et al., 2007)
Quantifying NP Exposure: What’s the Relevant Exposure Metric?
“Each One MayBe Right”
Schwartz et al. (2002)
Monteiller et al. (2006)
Stolzel et al. (2007)
Many Different Shapes, Chemistries, etc.
N. Walker, National Toxicology Program
Expanded List of Possible Measures of NP Exposure
• 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?
MSP Corp.NanoMOUDI-II
TSI 3007 Portable CPC
TSI 3550 NanoparticleSurface Area Monitor
EcoChem DC2000 CEDiffusion Charger
TEM/SEM
Particle Size Measurement
TSI 3034SMPS
MSP Corp.Wide-Range ParticleSpectrometer
Dekati Electrical Low Pressure Impactor (ELPI)
Met One HHPC-6Optical Particle Counter
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 g/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
– Potential for NP releases: Conventional>by pass>constant velocity
– Highly dependent on many variables- e.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
Pouring of 100 g Nanoalumina NPs
(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 real-world 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