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Measurement Methods for Nanoparticles Comparing and Contrasting Measurement Metrics

Measurement Methods for Nanoparticles Comparing and Contrasting Measurement Metrics . Presented at: National Environmental Partnership Summit May 20, 2008 Tim Johnson TSI Incorporated. Agenda. Nanoparticle exposure issues Lung deposition Traditional measurements

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Measurement Methods for Nanoparticles Comparing and Contrasting Measurement Metrics

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  1. Measurement Methods for NanoparticlesComparing and Contrasting Measurement Metrics Presented at: National Environmental Partnership Summit May 20, 2008 Tim Johnson TSI Incorporated

  2. Agenda • Nanoparticle exposure issues • Lung deposition • Traditional measurements • Nanoparticle measurements • Closing remarks • Questions, comments and discussion

  3. Nanoparticle Exposure • Increasing commercial development • Nano-scale materials exhibit startling new properties • Occupational health risks are not understood • Routes of exposure • Inhalation • Most common way for particles to enter the body • Lung deposition and health effects • Dermal contact • Ingestion • Current research indicates that mass and bulk chemistry may be less important than particle size, surface area, and surface chemistry (or activity) for nanostructured materials (Oberdörster et al. 1992, 1994a,b; Duffin et al. 2002)

  4. Nanoparticle Exposure What experts say If nanoparticles can • Deposit in the lung and remain there • Have active surface chemistry • Interact with the body Then, there is the potential for exposure related dosing

  5. Traditional IH Aerosol Measurements • No regulations for nanoparticles! • Traditional occupational exposure limits based on mass • Size range of ~0.1 – 100 µm • OSHA has two size fractions • ACGIH, ISO, and CEN define three size fractions • Mass based measurement methods • Gravimetric sampling (collecting particles on a filter) • Direct-reading instruments - Photometers

  6. Lung Deposition, Sampling and Modeling Size selective sampling • Size fractions and examples • Inhalable / total, ≤100 µm > silica • Thoracic, ≤10 µm > cotton dust • Respirable, ≤4 µm > coal dust • Human respiratory tract has 3 regions • Extrathoracic • Tracheobronchial • Alveolar • ICRP lung deposition models • Developed in 1966 • Used to develop current standards • Define and characterize lung deposition • Most recent work in 1999, by Drs. Phalen / Vincent (ACGIH) to develop a reference worker model • Reference worker lung deposition curves • Physiological, activity related, and aerosol parameters

  7. Lung Deposition Diagrammatic representation of respiratory tract regions in humans Based on International Commission of Radiological Protection (1994) and U.S. Environmental Protection Agency (1996a). Air Quality Criteria for Particulate matter, 2004, p 6-5.

  8. Why Monitor Nanoparticles? Quantifying Exposure • Quantifying worker exposure • Determining effectiveness of ventilation systems • Conduct work area monitoring • Assist in characterizing, defining, and validating new production processes • Selecting and implementing corrective actions Nanoparticle Research & Production Controls • Monitor and control particle concentration and size • Determine correlation between exposure and health effects

  9. Particle Measurements Nanoparticle General Sampling Practices • Look at outdoor concentrations for sources and variability • Ventilation system plays a role – Evaluate the effect • Background / baseline measurements Mass Measurements - Background • Traditional workplace exposure limits are mass based • No regulations currently exist specifically for nanoparticles • Mass of one 10 µm particle = 106 times the mass of one 100 nm particle = 109 times the mass of one 10 nm particle • Traditional gravimetric methods are not effective for nanoparticles since toxicity data is based on large particles It takes ~1,000,000,000 (1 billion) 10 nm particles to equal the mass of one 10 µm particle!

  10. Mass Measurements Background • Mass can be measured in many ways • Gravimetrically • Photometrically • Size selective sampling • PM10 • PM2.5 • PM1.0 • Inhalable, thorasic, respirable

  11. Photometry What is it? • Photometers measure particle mass in real time • Light-scattering effects vary based on particle properties • Photometers come in personal, hand held, table top, and fixed monitor configurations What it does? • Typical particle size range: 0.1 to 10 µm • Typical concentration range: 0.001 to 100 mg/m3 • Light-scattering technology closely estimates mass concentrations • Photometers respond linearly to mass concentration across their range

  12. Photometry Theory of Operation • Light- scattering laser photometry is used to determine mass concentration • Air sample is drawn into the sensing chamber • Laser is used to illuminate the particles • Particles scatter light in all directions • A lens collects light onto a photo-detector • Signal is proportional to the amount of light scattered, which is proportional to the mass concentration of the aerosol in mg/m3

  13. Gravimetric Strengths Area and personal samplers in the nano size range Ability to compare to historical gravimetric data Relatively inexpensive Air sampling equipment Lab analyses Gravimetric Weaknesses Mass measurements for nanoparticles are difficult due to size and sampling constraints Not a real-time measurement Takes time to get lab results Not able to use for point source location, etc. Toxicity for nanoparticles unknown May not have quantitative relevance as an exposure metric No guidelines or standards for nanoparticles Gravimetric Mass Measurements

  14. Photometer Strengths Qualitative relevance for agglomerated / aggregated nanoparticles: >100 nm Real-time measurement Field portable, battery operated, and easy to use Personal or area sampling Photometer Weaknesses Not in the size range for discrete nanoparticles:<100 nm Not size resolved Not a compliance method No guidelines or standards for nanoparticles Photometer Mass Measurements

  15. CPC Number Concentration CPC - what is it? • A Condensation Particle Counter (CPC) is an instrument for detecting and counting nanoparticles • CPCs do not size particles, only count them • CPCs measure number of nanoparticles in real time • A CPC uses a method of condensation and growth of particles until they are large enough to be optically detected • CPCs require a working fluid (alcohol or water) • Typical particle size range: 2.5 nm 1 µm • Concentration range: 0 – 500,000 pt/cc

  16. CPC Number Concentration Theory of Operation • Particles drawn into instrument • Particles pass through a saturator chamber mixing with vapor • Air flows through a condenser where vapor condenses onto the particles • Particles scatter laser light which is detected by a photo-detector

  17. CPC Strengths CPCs are well suited to measuring nanoparticles in the workplace Good qualitative measurements Based on relative changes in concentration Field portable, battery operated, and easy to use Handheld models relatively inexpensive ~ $5 – 8K CPC Weaknesses CPCs are not a size resolved measurement Cannot determine original size of particle Cannot account for agglomeration No guidelines or standards exist for number concentration of nanoparticles What’s a good number vs. a bad number CPC Number Concentration

  18. Size Distribution Background • Why measure size distribution of nanoparticles? • To know the size and number of nanoparticles produced for Exposure information and Quality control purposes • To determine if they are being released from production processes or being re-aerosolized during bulk production use • To determine if nanoparticles are agglomerating or aggregating after production • Size distribution can be measured in a number of ways • Scanning Mobility Particle Sizer (SMPS), <1 µm • Optical Particle Counter (OPC), >0.3 µm

  19. SMPS Size Technology What is it? • A SMPS uses a Differential Mobility Analyzer (DMA) and a CPC to measure size and number concentration of nanoparticles What it does? • DMA separates particles according to charge and electrical mobility for size classification • CPC grows the particles to a detectible size for counting • Has high resolution (64 channels/decade) and high size accuracy • Wide size range (2.5 – 1000 nm) • Wide concentration range (up to 108 particles/cm3)

  20. SMPS Technology Theory of Operation • Particles go through a inlet conditioner and a neutralizer • Creating a known charge distribution on the particles • Particles pass thru DMA • Particles are separated and classified according to electrical mobility size • Classified particles counted by a CPC • Particles are grown and counted in the CPC • Size distribution is determined

  21. SMPS Strengths Nanoparticle size range Real-time measurement Size distribution determined in several minutes Size resolved, quantitative measurement For process applications Determine if agglomerating Qualitative area sampling SMPS Weaknesses No guidelines or standards for nanoparticles Limited field portability Computer controlled Not your typical IH instrument SMPS Size Distribution

  22. OPC Technology What is it? • A OPC measures the size and number concentration of particles, > 0.3 mm • OPCs come in hand held, table top and fixed monitor configurations What it does? • OPCs measure particle size and number concentration by detecting light scattered from individual particles in real-time • OPCs may be able to measure nanoparticles in the workplace • Nanoparticles must have agglomerated/aggregated >0.3 µm in size • OPCs typically have multiple size fraction bins • OPC size bins can be arranged to simultaneously measure size fractions • Typical particle size range: 0.3 to 15 mm • Typical concentration range: 2x106 particles/ft3 (70 pt/cc)

  23. OPC Technology Theory of Operation • Single particles are drawn through a focused laser sheath and the resulting scattered light is collected by a mirror and focused on to a photo-detector • Concentration is derived from the count rate and particle size is derived from the pulse heights • Electronics have to be very fast to be able to count and distinguish particle sizes

  24. OPC Strengths For agglomerated/aggregated nanoparticles >300 nm Size resolved measurement Real-time measurement Qualitative area sampling Relative changes in number concentration Locate point sources Select and validate engineering controls Field portable, battery operated, and easy to use OPC Weaknesses Not in the size range for discrete nanoparticles, <0.3 µm No guidelines or standards for nanoparticles Limited to low concentration OPC Size Distribution

  25. Surface Area Measurements Background • Nanoparticles vs. large particles • Has relatively little mass, large surface area and large numbers • Nanoparticle exposure studies • Drs. Driscoll (1996) and Oberdörster (2001) have shown that surface area(μm2/cc)plays an important role in the toxicity of nanoparticles • Surface area is the metric that initial evidence shows correlates well with particle-induced adverse health effects • Potential for adverse health effects is proportional to particle surface area (Driscoll, 1996; Oberdörster, 2001) • Emerging need to assess workplace exposure to nanoparticles based on surface area

  26. Lung Deposition Diagrammatic representation of respiratory tract regions in humans • Lung Deposition – revisited • Inhalation is primary exposure route • The respiratory tract consists of 3 major regions • Extrathoracic region: uppermost region • Tracheobronchial (TB) region: middle region • Alveolar (A) region: innermost region • Uptake of inhaled particles according to deposition in respiratory tract Based on International Commission of Radiological Protection (1994) and U.S. Environmental Protection Agency (1996a). Air Quality Criteria for Particulate matter, 2004, p 6-5.

  27. Diffusion Charger Technology What it does? • A diffusion charger measures the charge of the particles. This charge calibrated to the surface area deposited in the TB or A regions of the lung • Does not measure the total surface area of particles sampled, only the TB or A deposition fractions • The ion trap voltages are optimized to correspond to the TB or A lung deposition curves for the reference worker • Particle size range: 10 – 1000 nm • Concentration range: TB = 1 – 2,500 µm/cc A = 1 – 10,000 µm/cc • User-selectable measurement response (TB or A)

  28. Diffusion Charger TechnologyBased on diffusion charging of sampled particles followed by detection using an electrometer Theory of Operation • Clean air is ionized • Diffusion Charging • Ions and aerosol sample streams are turbulently mixed and the particles are charged • Ion Trap • Excess ions are removed • Acts as an inlet conditioner or a size-selective sampler • Ion trap voltage can be changed between TB and A response

  29. Diffusion Charger Technology Theory of Operation (cont.) • Electrometer • Particles pass through the electrometer • Particles collected on a conductive filter • Amplifies and measures the charge on the surface of the particles • Measured charge converted into deposited surface area in units of µm2/cc

  30. Diffusion Charger Strengths Research shown that surface area is highly correlated with observed toxic effects Wide size range, 10- 1000 nm Real time measurement Qualitative area sampling Data correlates well with CPC and SMPS measurement trends Diffusion Charger Weaknesses Not size resolved Cannot determine original size of particle Cannot accountfor agglomeration No guidelines or standards for nanoparticles What’s a good number vs. a bad number Diffusion Charger Technology

  31. Particle Size Range for Aerosol Instruments Thoracic Inhalable (Total dust) TSP Respirable OPC Photometer CPC-alcohol Diffusion Charger SMPS CPC - Water 4 0.001 0.01 0.1 1 10 100 Particle Size Range (micrometers) OPC: Optical Particle Counter CPC: Condensation Particle Counter SMPS: Scanning Mobility Particle Sizer

  32. Application Comparison Photometer OPC CPC Diffusion charger Indoor Air Quality - Conventional Studies Good Good N/A N/A Indoor Air Quality - Ultrafine Particle Tracking Poor N/A Excellent N/A Industrial Workplace Monitoring (Conventional) Excellent Poor N/A N/A Industrial Workplace Monitoring (Nano-Materials) Poor1/Good2 Poor1/Good2 Excellent3 Excellent3 Outdoor Environmental Monitoring Good Good Excellent3 Excellent3 Emissions Monitoring Excellent Poor Good Excellent Respirator Fit Testing Excellent Poor Excellent N/A Filter Testing Excellent Excellent Excellent N/A Clean Room Monitoring Poor Excellent Excellent N/A 1 Engineered nano particles of homogenous material less than 0.1 micron (100 nm) in diameter. 2 Agglomerated and aggregated nano particles greater than 0.1 microns (100 nm) diameter for photometers and greater than 0.3 microns (300nm) for OPC’s. 3The Health effects of engineered nano particles and ultrafine particles below 0.1 micron (100 nm) in diameter are not completely understood. Research suggests these ultrafine particles may cause the greatest harm. There are currently no established exposure limits or governmental regulations specifically addressing ultrafine or nano particles exposure.

  33. Aerosol Technology Comparisons OPC = Optical Particle CounterCPC = Condensation Particle CounterSMPS = Scanning Mobility Particle Sizer1Surface area can be calculated using SPMS size distribution data.

  34. Research Work References • Donaldson, K. et al. Ultrafine (Nanometer) Particle Mediated Lung Injury, J. Aerosol Sci. 29(5/6):553-560. (1998) • Driscoll K.E. Role of inflammation in the development of rat lung tumors in response to chronic particle exposure. Inhal. Toxicol. 8 [suppl1: 85-98] (1996) • Driscoll K.E. et al. Pulmonary inflammatory, chemokine, and mutagenic responses in rats after subchronic inhalation of carbon-black. Toxicol. Appl. Pharmacol. 136, 372-380 (1996) • Driscoll K.E. et al. Characterizing mutagenesis in the hprt gene of rat alveolar epithelial-cells. Exp. Lung Res. 21, 941-956 (1995). • Heinrich et al. Chronic inhalation exposure of Wistar rats and two different strains of mice to diesel engine exhaust, carbon black, and titanium dioxide. Inhal. Toxicol. 7: 533-556 (1995) • Lam C.W. et al. Pulmonary toxicity of single-wall carbon nanotubes in mice 7 and 90 days after intratracheal instillation, Toxicol. Sci. 77 (1): 126-134 (2004) • Lee K.P. et al. Pulmonary response of rats exposed to titanium dioxide by inhalation for two years. Toxicol. Appl. Pharmacol. 79: 179-192 (1985) • Li N. et al. Ultrafine particulate pollutants induce oxidative stress and mitochondrial damage, Environ. Health Persp. 111:455-460 (2003) • Nemmar A. et al. Passage of inhaled particles into the blood circulation in humans, Circulation 105:411-414 (2002)

  35. Research Work References • Number A. et al. Passage of intratracheally instilled ultrafine particles from the lung into the systemic circulation in hamster. Am J Respir Crit Care Med (164) 1665-1668 (2001) 11. Oberdörster E. Manufactured nanomaterials (Fullerenes, C-60) induce oxidative stress in the brain of juvenile largemouth bass, Environ. Health Persp. 112 (10): 1058-1062 (2004) 12. Oberdörster G. Pulmonary effects of inhaled ultrafine particles. Int. Arch. Occup. Environ. Health 74:1-8 (2001) 13. Oberdörster, G. Significance of Particle Parameters in the Evaluation of Exposure-Dose-Response Relationships of Inhaled Particles, Particulate Sci. Technol. 14(2):135-151 (1996). 14. Oberdörster G. et al Association of particulate air pollution and acute mortality: involvement of ultrafine particles? Inhal. Toxicol. 7:111-124 (1995) 15. Penttinen P. et al. Number concentration and size of particles in urban air: effects on spirometric lung function in adult asthmatic subjects, Environ. Health Persp. 109:319-323 (2001) 16. Shanbhag, A. S. et al.Macrophage/Particle Interactions: Effect of Size, Composition and Surface Area, J. Biomed. Mat. Res. 28(1):81-90 (1994). 17. Utell M.J. et al. Acute health effects of ambient air pollution: the ultrafine particle hypothesis. J. Aerosol Med. 13:355-359 (2000). 18. Warheit D. B. et al. Comparative Pulmonary Toxicity Assessment of Single-wall Carbon Nanotubes in Rats, Toxicol. Sci. 77 (1): 117-125 (2004)

  36. Closing Remarks • Nanoparticle exposure is an issue of concern • Traditional measurements were discussed • Metrics for nanoparticle measurements were discussed along with available instruments • Applications of nanoparticle measurements • Review of bibliography of health effects studies

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