Engineered Nanomaterials and Occupational Health

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1 Engineered Nanomaterials and Occupational Health Andrew D. Maynard Chief Science Advisor Society of Toxicology, National Area Chapter. Novemb er 2nd 2005, Washington DC Woodrow Wilson Center, Project on Emerging Nanotechnologies

2 Focus on the Workplace Consumer perspective Occupational perspective Nano-based and nano-enabled products. Nanomaterials not readily accessible biologically in many cases. Example: Multi-walled carbon nanotube composites Production, handling and use of engineered nanomaterials. Exposure potential likely to be higher than in final products. Example: Handling single-walled carbon nanotubes Note: additional hazard potential may exist over the lifecycle of nano-enabled products Woodrow Wilson Center, Project on Emerging Nanotechnologies 2

3 Addressing Occupational Impact Exposure routes Exposure Characterization Dose Risk Control Reduced risk/impact Health Effects Toxicity Woodrow Wilson Center, Project on Emerging Nanotechnologies 3

4 Characterization and nano-toxicity screening Appropriate physicochemical characterization of nanomaterials used in toxicity screening tests is essential, if data are to be interpreted in relation to the material properties, inter-comparisons between different studies carried out, and conclusions drawn regarding hazard. Principles for characterizing the potential human health effects from exposure to nanomaterials: Elements of a screening strategy. Oberdörster et al. Particle and Fibre Toxicology 2:8 (2005) Woodrow Wilson Center, Project on Emerging Nanotechnologies 4

5 Potential Health Impact What makes nano different? Physical Structure Low High Influence of structure on potential health impact Liquids Gases & Vapors Low Macro-Materials Size Shape Surface Area Surface Activity Nano-Structure Conventional Understanding Compositional Structure Unconventional Understanding Nano-Materials & Devices Mass Composition High Woodrow Wilson Center, Project on Emerging Nanotechnologies 5

6 Engineered Nanomaterials - Structure is Important Example: Zinc Oxide nanostructures Materials Today June Zhong Lin Wang, Georgia Institute of Technology Woodrow Wilson Center, Project on Emerging Nanotechnologies 6

7 Setting Boundaries Engineered nanomaterials which potentially present new challenges! Criteria: Nanomaterials capable of entering or interacting with the body Nanomaterials which potentially exhibit nanostructure-dependent biological activity Nanoparticles Simple, complex, smart. Aerosols, powders, suspensions, slurries Comminution Aerosols from grinding, cutting, machining nanomaterials Agglomerates or aggregates of nanoparticles Degredation/Failure Aerosols and suspensions resulting from degradation and failure of nanomaterials Aerosolized suspensions Including slurries and solutions of nanomaterials? Unintentional use Potential exposure from unanticipated/unintentional use Woodrow Wilson Center, Project on Emerging Nanotechnologies

8 Airborne nanomaterials transformation Monodisperse coagulation second 1 minute 1 hour Number Concentration (cm -3 ) Time (seconds) Adapted from Hinds (1999) Woodrow Wilson Center, Project on Emerging Nanotechnologies 8

9 Agglomeration How does it affect particle biological activity? Agglomerated silver particles Agglomerated single walled carbon nanotubes Woodrow Wilson Center, Project on Emerging Nanotechnologies 9

10 Particle Categories Classes of engineered nanoparticles A. Spherical homogeneous D. Agglomerate homogeneous G. Heterogeneous agglomerate B. Fibrous homogeneous E. Heterogeneous concentric H. Active particle C. Non-spherical homogeneous F. Heterogeneous distributed I. Multifunctional particle (not necessarily inclusive) Woodrow Wilson Center, Project on Emerging Nanotechnologies 10

11 Measuring exposure Attribute + related physical quantity " exposure metrics Attribute 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 Particle Type A B C D E F G H I Associated metrics Mass Surface Area Number (Indicative only) Woodrow Wilson Center, Project on Emerging Nanotechnologies 11

12 Monitoring nanoscale aerosol exposures Options! Monitor mass concentration Continuity with the past Sensitivity and relevance issues! Monitor number concentration Relatively simple Difficult to differentiate between process-related and background aerosols Relevance?! Monitor aerosol surface area concentration Relevant for some materials Is this achievable? Woodrow Wilson Center, Project on Emerging Nanotechnologies 12

13 Mass Woodrow Wilson Center, Project on Emerging Nanotechnologies 13

14 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? Woodrow Wilson Center, Project on Emerging Nanotechnologies 14

15 Gravimetric analysis - sensitivity Example.! Conventional material: 5 mg/m 3 OEL! Nanomaterial: Particles are 100 times smaller Surface area is 100 times larger Possible nano-oel is 100 times lower - 50!g/m 3! 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/m 3.! Chemical speciation is an option Woodrow Wilson Center, Project on Emerging Nanotechnologies 15

16 Number Woodrow Wilson Center, Project on Emerging Nanotechnologies 16

17 Number-based Exposure Measurement! Portable Condensation Particle Counter Responds to particles larger than ~10 nm Very sensitive to low concentrations. Limited at high concentrations (10 5 particles/cm 3 for the TSI 3007) Background counts: can be as high as 10 6 particles/cm 3 and above Not material-specific Good for sniffing out sources 3007 Portable CPC, Woodrow Wilson Center, Project on Emerging Nanotechnologies 17

18 Example - non-specificity of number concentration Carbon black production - bag filling areas dn/dlog(d) (#/cm 3 ) Fork lift truck emissions Bagging Break Ratio Size distribution ratio Particle diameter (!m) Kuhlbusch et al. (2004) Woodrow Wilson Center, Project on Emerging Nanotechnologies 18

19 Surface Area Woodrow Wilson Center, Project on Emerging Nanotechnologies 19

20 Aerosol surface-area measurement Using attachment rate Charge on Aerosol! Surface Area + Ions DC2000 CE Diffusion Charger EcoChem Electrometer Woodrow Wilson Center, Project on Emerging Nanotechnologies 20

21 Monodisperse Test Particles Optional Generating f urnace Coagulation chamber Sintering f urnace DMA HPEA Generation (Silver Particles) Selection MFC Pure N 2 Carrier gas Fractal-like particles Spherical particles Increasing sintering temperature Ku, B. K. and Maynard, A. D. J. Aerosol Sci. 36 (9), , Woodrow Wilson Center, Project on Emerging Nanotechnologies 21

22 Comparison of measurement methods Monodisperse particles < 100 nm, fractal-like Measured projected area per particle (nm 2 ) nm Scanning Mobility Particle Sizer Transmission Electron Microscope Diffusion Charger (benchtop) Diffusion charger (portable) 1: Actual projected area per particle (nm 2 ) 100 nm Ku, B. K. and Maynard, A. D. J. Aerosol Sci. 36 (9), , Woodrow Wilson Center, Project on Emerging Nanotechnologies 22

23 Emerging Measurement Technologies Surface Area Size Distribution (Surface) Alveolar deposition Deposited Surface Area 0.6 Nanoparticle Surface Area Monitor Diffusion Charger Particle diameter / nm W ilson, W. E., in Proceedings of the 2004 Air and W aste Management Association C onference, Woodrow Wilson Center, Project on Emerging Nanotechnologies 23

24 Example: Handling nanotube material Unprocessed single walled nanotube material Woodrow Wilson Center, Project on Emerging Nanotechnologies 24

25 Aerosol characterization Single Walled Carbon Nanotubes Allotropes of carbon Tangles of nanotubes and nanoropes Nanotubes Nanoropes Catalyst particles Non-tubular carbon Raw single walled carbon nanotube material. Woodrow Wilson Center, Project on Emerging Nanotechnologies 25

26 Laboratory generation of nanotube aerosol Agitation of unprocessed material in an airflow Particle number concentration (dn/dlog(d) - arbitrary units) No Agitation 18% Agitation 36% Agitation 64% Agitation 91% Agitation Diameter /!m Agitation of unprocessed material in an airflow Maynard, A. D., P. A. Baron, et al. (2004). J. Toxicol. Environ. Health 67(1): Woodrow Wilson Center, Project on Emerging Nanotechnologies 26

27 Aerosol characterization Physical characteristics of airborne carbon nanotubes Particle number concentration (dn/dlog(d) - arbitrary units) No Agitation 18% Agitation 36% Agitation 64% Agitation 91% Agitation Expected Diameter /!m Measured Physical/Chemical Characteristics? Discrete carbon nanotubes or nanoropes? Transition metal catalyst particles? Non-tubular carbon? Woodrow Wilson Center, Project on Emerging Nanotechnologies 27

28 Aerosol Characterization Active specific surface area measurements Differential Mobility Analysis + Aerosol Particle Mass Analysis + Inertial deposition Electrostatic deposition -V -V Same mobility diameter ~3000 rpm + Measure surface area Specific surface area + Measure mass Woodrow Wilson Center, Project on Emerging Nanotechnologies 28

29 Aerosol Characterization Active specific surface area Concentration (Arbitrary) ? 31 nm mobility diameter particles nm diameter nanoropes 5 nm Fe particles Single nanotubes 30% Fe 5 nm amorphous carbon particles Active Specific Surface Area (m 2 /g) Single nanotubes no Fe Woodrow Wilson Center, Project on Emerging Nanotechnologies

30 Summary! Physical and chemical structure strongly influence the properties of engineered nanomaterials! Engineered nanomaterial hazard potential will likely be higher in the workplace than many other areas! Characterizing engineered nanomaterials in a health context presents many challenges, but is essential to understanding and managing potential impact.! Mass, surface-area and number concentration remain important exposure metrics! Inter-disciplinary collaboration is essential to understanding and managing potential risk Woodrow Wilson Center, Project on Emerging Nanotechnologies 30

31 Contact Information Dr Andrew D. Maynard Chief Science Advisor Project on Emerging Nanotechnologies Woodrow Wilson International Center for Scholars at the Smithsonian Institute One Woodrow Wilson Plaza 1300 Pennsylvania Ave. NW Washington DC Tel: URL: Woodrow Wilson Center, Project on Emerging Nanotechnologies 31