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