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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. Background. History of Carbon Nanotubes (CNTs).

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Carbon nanotubes risk assessment
Carbon Nanotubes Risk Assessment

The Secret Behind

Carbon Nanotubes (CNTs)

the Miracle Materials of the 21st Century


Regina Ma & Aster Zemenfeskidus

Winter 2010

History of carbon nanotubes cnts
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
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
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


A polymer-wrapped single-walled carbon nanotube


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 cnts
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
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
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
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 studies
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
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
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


  • 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 holders
Stake Holders

  • Occupational Safety & Health Professionals

  • Researchers

  • Policy Makers in government agencies & industry

  • Risk Assessors/Risk Evaluation Professionals

  • Workers in the Industry

Risk assessment
Risk Assessment

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

Who s at risk
Who’s At Risk?

  • Workers (the highest risk group)

  • Researchers

    • Immune-compromised

    • Elderly

    • Pregnant women

    • Children

Major routes of exposure
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





Nanotubes inside lung cells


Particles less than 5.0 microns are deposited in the lower respiratory tract

Case study ryan rasmussen et al
Case StudyRyan-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
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


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


Case study1
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


[1.6 fibers/cc/8hr] / [1000] = 0.0016 fibers/cc/8hr


[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 communication1
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 communication2
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 communication3
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
P.A. Community / Social Issues

NOT supportive of health or community

P a exposure issues
P.A. Exposure Issues

significant exposure

P a hazard toxicity
P.A. Hazard / Toxicity

Highly hazardous


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

Absence of evidence is not evidence of absence!”

- Plato