carbon nanotubes risk assessment
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Carbon NanotubesCarbon Nanotubes Risk Assessment Risk Assessment
The Secret Behind The Secret Behind Carbon Nanotubes (CNTs)Carbon Nanotubes (CNTs)
the Miracle Materials of the 21st Century the Miracle Materials of the 21st Century
ByRegina Ma & Aster Zemenfeskidus
Winter 2010
BackgroundBackground
History of Carbon Nanotubes History of Carbon Nanotubes (CNTs)(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?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 CNTsTypes of CNTsDivided 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 & MWCNTSWCNT & MWCNT
*TEM – Transmission Electron Microscopy
SWCNTSWCNT
A polymer-wrapped single-walled carbon nanotube
MWCNTMWCNT
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
Methods of Synthesis for Methods of Synthesis for CNTsCNTs
• 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 CNTsProperties of CNTsElectrical 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 CNTsApplication of CNTsElectronics
◦ 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.)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?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 StudiesAnimal StudiesFour 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
ResultsResults a day and/or a a day and/or a week after 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.)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
Stake HoldersStake HoldersOccupational Safety & Health
Professionals
Researchers
Policy Makers in government agencies & industry
Risk Assessors/Risk Evaluation Professionals
Workers in the Industry
Risk Risk
AssessmentAssessment
Hazard IdentificationHazard Identification
What are MWCNTs?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 EffectsHealth Effects
Carcinogenicity• lung irritation• chronic lung inflammation• exacerbation of asthma• formation of granulomas
GenotoxicityGenotoxicity
• formation of oxygen radicals DNA damage:
Fibrosis Lung cancer (?)
• shape and size of aromatic ring systems interfere with functions of DNA cancer
CytotoxicityCytotoxicity
• 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?Who’s At Risk?Workers (the highest risk group)
Researchers
Immune-compromised
Elderly
Pregnant women
Children
Exposure Exposure AssessmentAssessment
Major Routes of ExposureMajor Routes of Exposure
Inhalation 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 RoutesExposure Routes
Inhalation
Dust
Dermal
Sunscreens containing ZnO & TiO
Ingestion
Food (donuts)
Ocular
Dust
InhalationInhalation
Nanotubes inside lung cells
Nanotubes
Nucleus
cytoplasm
Particles less than 5.0 microns are deposited in the lower respiratory tract
InhalationInhalation
Dose-Response Dose-Response AssessmentAssessment
Case StudyCase Study Ryan-Rasmussen et al.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 StudyCase StudyConversion 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 StudyCase StudyUncertainty
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 numbersabove were based on whether adverse health effects were
observed during the experiment.
Risk Management & Risk Management & CommunicationCommunication
• 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 & Risk Management & CommunicationCommunication
Risk Management & Risk Management & CommunicationCommunication
• 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 & Risk Management & CommunicationCommunication
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 IssuesP.A. Community / Social Issues
InitialCommunity / Social
IssuesScore
Evaluate effects on Community and related social Issues
G G=Goal 21-a lot, 2-some, 3-little. Does this move forward the goal of human and environmental health?
N N=Need 11-a lot, 2-some, 3-little or not sure. Ask the question: Is it necessary? Do we really need this?
F F=Future Generations 31-little, 2-some, 3-high impact. Is there a potential impact on future generations of humans and other species?
DD=Democratic, 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 A=Alternatives 31-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
P.A. Exposure IssuesP.A. Exposure IssuesInitial Exposure Issues Score Evaluate potential exposure issues
E E=Exposure 20-none, 1-little, 2-some, 3-high. Do we have control over the exposure?
M M=Multiple exposures 20-none, 1-little, 2-some, 3-high. Is there exposure to other chemicals with similar hazard?
Ch Ch=Children exposed 30-none, 3-little, 5-some or high or don't know. Children are often more vulnerable. Are children being exposed.
CP CP=Consumer products 30-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 30-no occupational exposure, 1-little, 2-some, 3- a lot or do not know. Is there occupational exposure?
F F=Food exposure 20-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
P.A. Hazard / ToxicityP.A. Hazard / Toxicity Initial
Hazard / Toxicity
Score Evaluate potential hazards
H H=Hazard 101-low, 5-some, 10-high. Follow classical hazard evaluation, pick endpoint, exam relevant quality studies (cancer, reproductive, neurotoxicity, irreversible)
IS IS=Individual Sensitivity 21-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 31-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 31-little persistence 2-some, 3-a lot of persistence or do not know. Is the compound presistent in the environment?
B B=Bioaccumulate 31-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 hazard30-significant hazards or unknowns, serious concern
Highly hazardous
Precautionary ApproachPrecautionary ApproachFinal Results
Community / Social Issues 12/15
Exposure Issues 15/20
Hazard / Toxicity 28/30
Total 55/65
Precautionary PrinciplePrecautionary Principle
MediaMedia
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
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