Carbon Nanotubes Risk Assessment

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Carbon Nanotubes Risk Assessment

• The Secret Behind
• Carbon Nanotubes (CNTs)
• the Miracle Materials of the 21st Century
• By
• Regina Ma Aster Zemenfeskidus
• Winter 2010

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Background
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History of Carbon Nanotubes (CNTs)

• 1991 MWCNTs (Multi-Walled Carbon Nanotubes)
  discovered by Japanese physicist, Sumio Iijima,
  at Nippon Electronics Corporation (NEC). While he
  was studying the material deposited on the
  cathode during the arc-evaporation synthesis of
  fullerenes, he found that the central core of the
  cathodic deposit contained a variety of closed
  graphitic structures including nanoparticles and
  nanotubes
• 1996 Richard Smalley his group at Rice
  University described an alternative method of
  preparing SWCNTs (Single-Walled Carbon
  Nanotubes).
• 2002 Study from UC Berkeley incorporated the
  use of a suspended testing device to measure
  CNTs thermal conductivity.
• 2003 President Bush signed a bill authorizing
  U.S. Nanotechnology Research Development Act

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What are CNTs?

• Popular products of nanotechnology
• Size ranging from 1100 nanometer (nm)
• Wide range of length / diameter ratio
• Large surface area / volume ratio
• Structurally similar to rolled-up graphite sheets
  and/or fullerene
• With carbon atoms bonding in an sp2 hybridization
• Light as plastic and stronger that steel
• Some CNTs are similar in shape to asbestos fibers

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Types of CNTs

• Divided into two major categories
• Single-Walled Carbon Nanotubes (SWCNTs) formed
  from a single layer
• Multi-Walled Carbon Nanotubes (MWCNTs) contain
  several concentric cylinders or cylinders inside
  other cylinders
• Note In each case, the form of nanotube is
  identified by a sequence of two numbers, the
  first one of which represents the number of
  carbon atoms around the tube, while the second
  identifies an offset of where the nanotube wraps
  around to.

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SWCNT MWCNT
TEM Transmission Electron Microscopy
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SWCNT
A polymer-wrapped single-walled carbon nanotube
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MWCNT
High-resolution transmission electron
microscopy (HRTEM) images of Ag-nanoparticles
deposited on N-doped and undoped carbon
nanotubes (a) Ag-nanoparticles (2-5 nm in
diameter) deposited on CNxMWNTs. The image
reveals a nanotube bundle which is uniformly
coated with Ag-nanoparticles, and (b) Ag
nanoparticles (10-20 nm in diameter) poorly
coating carbon MWNTs (undoped) the latter sample
was produced by the reduction of Silver nitrate
(AgNO3) in DMF in presence of MWCNTs. Note the
clear absence of Ag-nanoparticles covering the
undoped material. dope - altering properties
of the tube so as to alter the electronic,
mechanical and chemical properties of the tubes
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Methods of Synthesis for CNTs

• Cite arc evaporation - extrusion nanotubes
  condensed near an arc evaporation source under
  high gravity condition
• Laser ablation - removal of material from the
  surface of an object by vaporization, chipping or
  other erosive processes
• High pressure carbon monoxide
• Sputtering, Chemical Vapor Deposition (CVD) - a
  process by which gas-phase molecules are
  decomposed to reactive species, leading to film
  or particle size
• Plasma Enhanced Chemical Vapor Deposition
  (PECVD) - a process employing a low pressure by
  which films are converted from a gas or vapor
  state to a solid state, that is, following the
  formation of plasma from the reacting substances

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Properties of CNTs

• Electrical conductivity
• Conductivity of 1000x stronger than copper
• Used as semi-conductors or insulators
• Thermal conductivity
• High thermal conductivity along axis
• Mechanical strength
• Super strong carbon fibers containing layers
  formed by strong covalent bonds
• Tensile strength 100x greater than steel

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Application of CNTs

• Electronics
• Used as batteries in electric cars
• Energy
• Materials for electrodes in batteries
• Life Sciences
• Water purification
• As aptamers for drugs to bind target molecules
• ATP detection in living cells

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Application of CNTs (cont.)

• Products
• Wound dressings
• Medical tools
• Tennis rackets
• Golf club
• car brakes and body panels
• Yacht masts Bike frames
• Sunscreen Anti-aging creams
• Computers
• Bullet-proof vest

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What are the Hazards?

• Human Risk
• mainly from inhalation of the CNTs that have
  large Surface Area/Volume ratio (smaller particle
  higher the Surface Area/Volume ratio) ? more
  particles in respirable area
• Environmental Risk
• Carbon fibers can form colloidal solutions
  (chemical substance where one substance is
  dispersed evenly throughout another) when surface
  structure is altered. Can be transported
  anywhere.
• Can bind easily to heavy metals such as uranium
  which is abundant in environment and water
• Asharani et al.
• phenotypic defects in zebrafish embryos at 60
  µg/ml of MWCNTs
• Slimy mucus like coating around embryos above 60
  µg/ml of MWCNTs
• Apoptosis, delayed hatching and formation of
  abnormal spinal cords at high concentrations of
  MWCNTs

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Animal Studies

• Four groups of mice (Poland et al.)
• First group injected with short nanotubes about 5
  microns in length
• Second group injected with long nanotubes about
  20 microns in length
• Third group injected with asbestos
• Fourth group injected with small carbon clumps

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Results a day and/or a week after

• Mice injected with the short nanotubes or small
  carbon clumps did not develop diseases
• Those injected with long nanotubes and asbestos
  fibers developed lesions on the tissue lining
• Note these results indicate that lesions caused
  by the long nanotubes would have developed into
  mesothelioma (cancer of lung lining)

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Animal Studies (cont.)

• Five groups of mice (Poland et al.)
• One group had long, straight MWCNTs injected into
  abdominal cavity
• Second group had asbestos fibers with high aspect
  ratio
• Third group had short asbestos fibers
• Fourth group had nanoparticulate carbon black
• Fifth group had short or tangled MWCNTs
• Results
• inflammatory reaction and formation of granulomas
  (small nodules of cells that form around foreign
  bodies) caused by asbestos fibers with high
  aspect ratio and long, straight MWCNTs
• Little or no inflammation for others
• Source Nature Nanotechnology

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Stake Holders

• Occupational Safety Health Professionals
• Researchers
• Policy Makers in government agencies industry
• Risk Assessors/Risk Evaluation Professionals
• Workers in the Industry

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Risk Assessment
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Hazard Identification
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What are MWCNTs?

• multiple stacked single-walled carbon nanotubes
  with diameters ranging from 2-100 nm
• long, thin multi-walled carbon nanotubes that
  look like asbestos fibers, behave like asbestos
  fibers
• 'needle-like' shape
• low solubility and biopersistent

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Health Effects Health Effects
Carcinogenicity lung irritation chronic lung inflammation exacerbation of asthma formation of granulomas
Genotoxicity formation of oxygen radicals DNA damage Fibrosis Lung cancer (?) shape and size of aromatic ring systems interfere with functions of DNA ? cancer
Cytotoxicity depends on the geometry in which cytotoxic effect depends on time- and dose-relationship. apoptosis - death of various human cell lines caused by non-specific association with hydrophobic regions of the cell surface and internalization by endocytosis and accumulation in the cytoplasm of the cell. DNA then wraps around the nanotubes resulting in cell death
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Whos At Risk?

• Workers (the highest risk group)
• Researchers
• Immune-compromised
• Elderly
• Pregnant women
• Children

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Exposure Assessment
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Major Routes of Exposure

• Inhalation
• Transdermal absorption
• Ingestion
• Ocular
• Note hazardous health effects, hence, depend
  on the route of exposure and the type of the
  nanoparticle to which an individual or animal is
  being exposed

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Exposure Routes
Inhalation Dust Dermal Sunscreens containing ZnO TiO Ingestion Food (donuts) Ocular Dust
 

•  

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Inhalation
Nanotubes
Nucleus
cytoplasm
Nanotubes inside lung cells
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Inhalation
Particles less than 5.0 microns are deposited in
the lower respiratory tract
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Dose-Response Assessment
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Case Study Ryan-Rasmussen et al.

• Animal Study (single exposure)
• Expose mice to MWCNTs (30mg/m3 and 1mg/m3)
• Migration from alveoli of lungs to pleura
  (tissues that line outside of lungs) ? fibrosis
• Cluster of immune cells (lymphocytes and
  monocytes) on pleura surface within one day of
  inhalation
• Localized fibrosis (scarring on parts of pleura
  surfaces) ? two weeks after inhalation. This is
  found in asbestos exposure

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Case Study

• Conversion used 1 fiber/cc 5mg/m3
• Occupational Safety and Health Administration
  Permissible
• Exposure Limit (OSHA PEL) for graphite
  5mg/m3/8hr 1
• fibers/cc/8hr
• American Conference of Industrial Hygienists
  Threshold Limit
• Value (ACGHI TLV) for asbestos 0.1 fibers/cc/8hr
• OSHA PEL for asbestos 0.1 fibers/cc/8hr
• National Institute for Occupational Safety and
  Health
• Recommended Exposure Limit (NIOSH REL) for
  asbestos 0.1
• fibers/cc/8hr

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Case Study
Uncertainty Factors Uncertainty Factors
Inadequate Animal Data 10
Animal to Human Extrapolation 10
Human Variability 10
Total 1000
NOAEL? from animal study 1mg/m3/6hr 1.6
fibers/cc/8hr LOAEL? from animal study
30mg/m3/6hr 8 fibers/cc/8hr NOAEL? 1.6
fibers/cc/8hr / 1000 0.0016
fibers/cc/8hr LOAEL? 8 fibers/cc/8hr /
1000 0.008 fibers/cc/8hr Compared with
ACGHI TLV, NIOSH REL, OSHA PEL for asbestos 0.1
fibers/cc/8hr OSHA PEL for graphite 1
fibers/cc/8hr Note No NOAEL and LOAEL for
MWCNTs. The numbers above were based on whether
adverse health effects were observed during the
experiment.
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Risk Management Communication
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Risk Management Communication

• More inhalation studies conducted to determine if
  MWCNTs cause mesothelioma
• Need to perform studies with continuous exposure
  since single exposure resulted in disappearance
  of fibrosis and immune response in 3 months.
• Repeat experiment with asbestos as positive
  control, various doses, different strains of
  mice, and other species such as rats.
• Need to conduct human studies in workplaces with
  continuous exposures and study health effects in
  humans

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Risk Management Communication

• Monitor workplace air during processing
  operations
• Training in working procedures handling and
  manufacturing of MWCNTs
• Train workers to use Personal Protective
  Equipment (PPE) such as respirators and gloves
• Routine checkups of workers health
• Manufacture in closed chemical reactors
• Avoid large-scale production
• Use and update engineering controls
• Educate public and workers with pamphlets,
  flyers, talks

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Risk Management Communication

• Write to legislatures, senators and
  representatives to halt the use of nanoparticles
  in products until there are enough evidence to
  indicate theyre safe
• Contact manufacturers and ask them to stop
  incorporating nanoparticles into their products
  until the government has declared theyre safe to
  use

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P.A. Community / Social Issues
Initial Community / Social Issues Score Evaluate effects on Community and related social Issues
G GGoal 2 1-a lot, 2-some, 3-little. Does this move forward the goal of human and environmental health?
N NNeed 1 1-a lot, 2-some, 3-little or not sure. Ask the question Is it necessary? Do we really need this?
F FFuture Generations 3 1-little, 2-some, 3-high impact. Is there a potential impact on future generations of humans and other species?
D DDemocratic, community based process 3 1-a lot of community involvement and consultation, 2-some, 3-little. Was the community consulted early and often in the process? Was the process democratic and inclusive.
A AAlternatives 3 1-alternatives were carefully considered, 2-some consideration, 3-no consideration. Where alternatives considered?
  Total 12/15 5-good, supportive of health and community15-poor, not supportive of health or community
NOT supportive of health or community
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P.A. Exposure Issues
Initial  Exposure Issues  Score Evaluate potential exposure issues
E EExposure 2 0-none, 1-little, 2-some, 3-high. Do we have control over the exposure?
M MMultiple exposures 2 0-none, 1-little, 2-some, 3-high. Is there exposure to other chemicals with similar hazard?
Ch ChChildren exposed 3 0-none, 3-little, 5-some or high or don't know. Children are often more vulnerable. Are children being exposed.
CP CPConsumer products 3 0-not in consumer products, 1-little, 2-some, 3- a lot or do not know. Is this compound in consumer prodcucts?
O OOccupational exposure 3 0-no occupational exposure, 1-little, 2-some, 3- a lot or do not know. Is there occupational exposure?
F FFood exposure 2 0-not in food supply, 1-little, 2-some, 3- a lot or do not know. Is the compound present in the food supply.
  Total 15/20 0-no exposure, no problems20-significant exposure, serious concern
significant exposure
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P.A. Hazard / Toxicity
 Initial  Hazard / Toxicity  Score  Evaluate potential hazards
H HHazard 10 1-low, 5-some, 10-high. Follow classical hazard evaluation, pick endpoint, exam relevant quality studies (cancer, reproductive, neurotoxicity, irreversible)
IS ISIndividual Sensitivity 2 1-little 2-some, 3-a lot. Determine if any individuals are more sensitive than health adult such as the very young or old.
EC ECEcological hazard 3 1-little 2-some, 3-a lot. Is it a hazard to other species or the environment?
V VVolume 5 how much is produced (1research only, 2lt1000 lbs, 3lt10,000, 4lt100,000, 5gt100,000 or do not know)
P PPersistent 3 1-little persistence 2-some, 3-a lot of persistence or do not know. Is the compound presistent in the environment?
B BBioaccumulate 3 1-little 2-some, 3-a lot. Does it bioaccumulative in humans or animals or move up the food chain?
UC UCUncertainty 2 1-little 2-some, 3-a lot. How certain is the information?
  Total 28/30 7-low hazard30-significant hazards or unknowns, serious concern
Highly hazardous
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Precautionary Approach
Final Results Final Results
Community / Social Issues 12/15
Exposure Issues 15/20
Hazard / Toxicity 28/30
Total 55/65
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Precautionary Principle
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Media
Louis Brus and Sumio Iijima received the Kavli
Prize in nanoscience at an award ceremony in
Oslo, Noway in September 2008. In the middle Fred
Kavli who initiated the prize.
The inhalation of asbestos fibres can cause lung
diseases and cancers
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- Bill Proud
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• Absence of evidence is not evidence of absence!
• - Plato

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