Carbon Nanotubes
Risk Assessment
The Secret Behind
Carbon Nanotubes (CNTs)
the Miracle Materials of the 21st Century
By
Regina Ma & Aster Zemenfeskidus
Winter 2010
Background
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
What are CNTs?

Popular products of nanotechnology

Size ranging from 1–100 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
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.
SWCNT & MWCNT
*TEM – Transmission Electron Microscopy
SWCNT
A polymer-wrapped single-walled carbon nanotube
MWCNT
High-resolution transmission electron microscopy (HRTEM) images of Ag-nanoparticles deposited on Ndoped 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
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
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
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
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
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
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
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)
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
Stake Holders

Occupational Safety & Health Professionals

Researchers

Policy Makers in government agencies &
industry

Risk Assessors/Risk Evaluation Professionals

Workers in the Industry
Risk
Assessment
Hazard Identification
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
Health Effects
Carcinogenicity
Genotoxicity
Cytotoxicity
• lung irritation
• chronic lung inflammation
• exacerbation of asthma
• formation of granulomas
• formation of oxygen radicals
DNA damage:
Fibrosis
Lung cancer (?)
• shape and size of aromatic ring systems
interfere with functions of DNA  cancer
• 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
Who’s At Risk?

Workers (the highest risk group)

Researchers

Immune-compromised

Elderly

Pregnant women

Children
Exposure Assessment
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
Exposure Routes
Inhalation
Dermal
Ingestion
Ocular
Dust
Sunscreens
containing
ZnO & TiO
Food
(donuts)
Dust
Inhalation
Nanotubes
Nucleus
cytoplasm
Nanotubes inside lung cells
Inhalation
Particles less than 5.0 microns are deposited in the lower respiratory tract
Dose-Response
Assessment
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
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
Case Study
NOAEL? from animal study:
1mg/m3/6hr = 1.6 fibers/cc/8hr
LOAEL? from animal study:
30mg/m3/6hr = 8 fibers/cc/8hr
Uncertainty
Factors
Inadequate
Animal Data
10
Animal to
Human
Extrapolation
10
Human
Variability
10
Total
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.
1000
Risk Management &
Communication
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
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
•
Risk Management & Communication

Write to legislatures, senators and representatives to
halt the use of nanoparticles in products until there are
enough evidence to indicate they’re safe

Contact manufacturers and ask them to stop
incorporating nanoparticles into their products until the
government has declared they’re safe to use
P.A. Community / Social Issues
Initial
Community / Social
Issues
Score
Evaluate effects on Community
and related social Issues
G
G=Goal
2
1-a lot, 2-some, 3-little. Does this move forward
the goal of human and environmental health?
N
N=Need
1
1-a lot, 2-some, 3-little or not sure. Ask the
question: Is it necessary? Do we really need this?
3
1-little, 2-some, 3-high impact. Is there a potential
impact on future generations of humans and other
species?
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.
3
1-alternatives were carefully considered, 2-some
consideration, 3-no consideration. Where
alternatives considered?
12/15
5-good, supportive of health and community
15-poor, not supportive of health or community
F
D
A
F=Future Generations
D=Democratic, community based
process
A=Alternatives
Total
NOT supportive of health or community
P.A. Exposure Issues
Initial
Exposure Issues
Score
Evaluate potential exposure issues
E
E=Exposure
2
0-none, 1-little, 2-some, 3-high. Do we have control over
the exposure?
M
M=Multiple exposures
2
0-none, 1-little, 2-some, 3-high. Is there exposure to other
chemicals with similar hazard?
Ch
Ch=Children exposed
3
0-none, 3-little, 5-some or high or don't know. Children
are often more vulnerable. Are children being exposed.
CP
CP=Consumer 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
O=Occupational exposure
3
0-no occupational exposure, 1-little, 2-some, 3- a lot or
do not know. Is there occupational exposure?
F
F=Food 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 problems
20-significant exposure, serious concern
significant exposure
P.A. Hazard / Toxicity
Hazard /
Toxicity
Initial
Score
Evaluate potential hazards
H
H=Hazard
10
1-low, 5-some, 10-high. Follow classical hazard evaluation, pick
endpoint, exam relevant quality studies (cancer, reproductive,
neurotoxicity, irreversible)
IS
IS=Individual 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
EC=Ecological hazard
3
1-little 2-some, 3-a lot. Is it a hazard to other species or the
environment?
V
V=Volume
5
how much is produced (1=research only, 2=<1000 lbs, 3=<10,000,
4=<100,000, 5=>100,000 or do not know)
P
P=Persistent
3
1-little persistence 2-some, 3-a lot of persistence or do not know.
Is the compound presistent in the environment?
B
B=Bioaccumulate
3
1-little 2-some, 3-a lot. Does it bioaccumulative in humans or
animals or move up the food chain?
UC
UC=Uncertainty
2
1-little 2-some, 3-a lot. How certain is the information?
Total
28/30
7-low hazard
30-significant hazards or unknowns, serious concern
Highly hazardous
Precautionary Approach
Final Results
Community / Social Issues
12/15
Exposure Issues
15/20
Hazard / Toxicity
28/30
Total
55/65
Precautionary Principle
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
- Bill Proud
“Absence of evidence is not
evidence of absence!”
- Plato