Transcript Carbon Nanotubes Risk Assessment The Secret Behind Carbon Nanotubes (CNTs)
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 N doped and undoped carbon nanotubes:
(a)
Ag-nanoparticles (2-5 nm in diameter) deposited on CN x MWNTs. 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 (AgNO 3 ) 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
Carcinogenicity Genotoxicity Cytotoxicity
Health Effects
• • • • 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
Inhalation Dust
Exposure Routes
Dermal Sunscreens containing ZnO & TiO Ingestion Food (donuts) Ocular 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/m 3 and 1mg/m 3 ) 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/m 3 Occupational Safety and Health Administration Permissible Exposure Limit (OSHA PEL) for graphite: 5mg/m 3 /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/m 3 /6hr = 1.6 fibers/cc/8hr
LOAEL? from animal study
: 30mg/m 3 /6hr = 8 fibers/cc/8hr
NOAEL?: Uncertainty Factors
Inadequate Animal Data Animal to Human Extrapolation Human Variability 10 10 10 Total [1.6 fibers/cc/8hr] / [1000] =
0.0016 fibers/cc/8hr
1000
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.
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
G
Community / Social Issues
G=Goal N N=Need F F=Future Generations
Score
2 1 3
Evaluate effects on Community and related social Issues
1-a lot, 2-some, 3-little. Does this move forward the goal of human and environmental health?
1-a lot, 2-some, 3-little or not sure. Ask the question: Is it necessary? Do we really need this?
1-little, 2-some, 3-high impact. Is there a potential impact on future generations of humans and other species?
D D=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 Total 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
NOT
supportive of health or community
Initial Exposure Issues
E E=Exposure M Ch CP O F M=Multiple exposures Ch=Children exposed CP=Consumer products O=Occupational exposure F=Food exposure Total
P.A. Exposure Issues
Score
2
Evaluate potential exposure issues
0-none, 1-little, 2-some, 3-high. Do we have control over the exposure?
2 3 3 3 2
15/20
0-none, 1-little, 2-some, 3-high. Is there exposure to other chemicals with similar hazard?
0-none, 3-little, 5-some or high or don't know. Children are often more vulnerable. Are children being exposed.
0-not in consumer products, 1-little, 2-some, 3- a lot or do not know. Is this compound in consumer prodcucts? 0-no occupational exposure, 1-little, 2-some, 3- a lot or do not know. Is there occupational exposure?
0-not in food supply, 1-little, 2-some, 3- a lot or do not know. Is the compound present in the food supply. 0-no exposure, no problems 20-significant exposure, serious concern
significant
exposure
Initial
H IS
Hazard / Toxicity
H=Hazard
P.A. Hazard / Toxicity
IS=Individual Sensitivity EC EC=Ecological hazard V P B V=Volume P=Persistent B=Bioaccumulate UC UC=Uncertainty Total
Score Evaluate potential hazards
10 2 3 5 3 3 1-low, 5-some, 10-high. Follow classical hazard evaluation, pick endpoint, exam relevant quality studies (cancer, reproductive, neurotoxicity, irreversible) 1-little 2-some, 3-a lot. Determine if any individuals are more sensitive than health adult such as the very young or old.
1-little 2-some, 3-a lot. Is it a hazard to other species or the environment? how much is produced (1=research only, 2=<1000 lbs, 3=<10,000, 4=<100,000, 5=>100,000 or do not know) 1-little persistence 2-some, 3-a lot of persistence or do not know. Is the compound presistent in the environment?
1-little 2-some, 3-a lot. Does it bioaccumulative in humans or animals or move up the food chain?
2 1-little 2-some, 3-a lot. How certain is the information?
28/30
7-low hazard 30-significant hazards or unknowns, serious concern
Highly
hazardous
Precautionary Approach
Final Results
12/15
Community / Social Issues Exposure Issues Hazard / Toxicity Total
15/20 28/30
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