Carbon nanotube structure - Wikipedia 8 March 2010Nanotechnology & Carbon Nanotube Hazards

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Nanomaterials hazard investigation & management:

This document discusses possible health & environmental concerns associated with nanotechnology and the production of products that may release ultra-fine particles such as carbon nanotubes produced by nanotechnology operations & research.

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What Are Current Estimates of Health Risks from Carbon Nanotube Particle Exposure?

Here we report on studies of possible health risks from products or processes involving carbon nanotubes both in the general environment and in the occupational, industrial, or research laboratory environment. Page top image of a carbon nanotube structure: Wikipedia [15].


What are Carbon Nanotubes?

Carbon nanotubes (CNT) are cylindrical structures (tubes) of carbon allotropes whose tube diameter is just one to a few nanometers wide (for single-walled nanotubes or SNWT). For a point of size contrast, a human hair is typically 20-50 microns in diameter. A 1-nanometer in diameter carbon nanotube is about - about 1/20,000 to 1/50,000 the thickness of a typical human hair. Multi-walled carbon nanotubes (MWNT) (multiple layers or concentric single-walled nanotubes) are also produced that have greater resistance to chemicals.

According to solid-state physicist Wolfgang S. Bacsa, Russian LV Radushkevich and collaborators reported about carbon nanotubes as early as 1952. M Endo from Japan, collaborating with A Oberlin in France, reported on the observation of carbon nanotubes by electron microscopy in 1976. A more contemporary and key researcher too-often credited with the "discovery" of carbon nanotubes was Suomo Iijima, a Japanese scientist working at NEC in 1991.

Because carbon nanotubes can be produced in very long lengths and because they can be assembled into strong, chemically-resistant structures with useful electrical properties, they may be used for a variety of uses including medical, electronic, and other industrial applications.

What are Nanomaterials?

Individual single-wall carbon nanotubes (SWNTs) or multi-wall carbon nanotubes can be assembled into more complex materials. The individual nanotubes measure in nanometers of height and width. Carbon nanotubes may be assembled into larger structures for various purposes.

In 2012 the New York Times reported on rising concern for the need for better research into potential risks associated with nanomaterials - extremely small particles of a variety of substances, typically metals such as silver, carbon, zinc, or aluminum have been used to add desirable properties to products (such as cosmetics, clothing, and paint) that have reached the marketplace in the decade beginning in 2002.[1]

The National Research Council (NRC) of the National Academy of Sciences (NAS) has convened a panel of experts to research potential risks associated with nanomaterials. The Times elaborated that the panel has called for research in four areas [paraphrasing]:

  1. Identification of sources of release of nanomaterials into the environment
  2. Processes that affect exposure to nanomaterials and related hazards
  3. The interactions of nanomaterials at subcellular all the way to ecosystem-wide levels
  4. Ways to acclerate the progress of nanomaterials risk assessment research

CEINT, the Center for Environmental Implications of Nano Technology, hosted at Duke University, explores "the relationship between a vast array of nanomaterials— from natural, to manufactured, to those produced incidentally by human activities— and their potential environmental exposure, biological effects, and ecological impacts.". [17]

General Environmental Exposure to Carbon Nanotube Materials

Presently (May 2010) a partial review of the literature suggests that the probability of exposure to carbon nanotube materials [CNM] in the general environment is very low, but there is a potential exposure in research and industrial environments where these materials are used, studied, or produced.

Detection of Carbon Nanotube Materials in the Environment

Typically carbon nanotube material (CNM) particles likely to be detected in an environment where they are produced or studied are larger than a single nanotube diameter. Carbon nanotube particles that may be released during production or laboratory studies are about 0.3 microns in size.

Carbon nanotube particles in this 0.3um size range are well under the one-micron size that is commonly the smallest particle easily detected by optical light microscopy used in most forensic laboratories. Transmission electron (TEM) microscopy, SEM microscopy, or similar methods must be employed to detect these particles.

Reports of Possible Health Effects of Exposure to Carbon Nanotube Materials

Comparing Carbon Nanotube Material Particles to Asbestos Particles

Asbestos particles in air are typically 0.7 microns to 70 microns in size, primarily depending on fiber length and whether or not the particles are comprised of clusters of fibers or individual fibers. See ASBESTOS FLOOR TILE LAB PROCEDURES for photos of asbestos particles and fibers.

Carbon nanotube particles may be as small as a single nanometer in size but of considerable length, possibly similar in that regard to small asbestos fibers.

Because a component of the airborne asbestos fiber hazard is the inhalation of very small inorganic fibers into the lung where they may over time cause lung disease, or mesothelioma (a rare cancer caused almost exclusively by exposure to asbestos fibers that are inhaled or ingested into the body), it is natural to ask the question of whether or not carbon nanotube particles in the environment, or in the occupational environment might pose similar hazards.

Also, as we report below, an occupational exposure to chemicals used in the fabrication or study of carbon nanotube materials may also be a hazard.

In 2008 the New York Times reported that to date no illnesses have been reported concerning nanotube-containing articles and that current popular consumer products such as tennis rackets that contain nanotubes are of little risk to consumers. But because nanotube-based fibers are very small, they could pose a health risk. [3]

Consumer caution (not fear) are advised. Carbon nanotubes include bundles of fibers that are similar to but more uniform than naturally-occurring asbestos fibers, as reported on an article published at the website of the journal Nature Nanotechnology that appeared on 5/21/08.

Another article published at by the same journal stated: "The toxicity of carbon nanotubes is the subject of ongoing debate. A preliminary study using a small number of mice shows that they may be safe, but the results should be treated with caution." The article also indicated an urgent need for a framework for to assessment of risks of carbon nanotubes on human health for methods of reliable risk assessment of nanotube materials.

As we learned from the history of asbestos-related illness and mesothelioma, the greatest risk, if one is ultimately demonstrated at all for nanotube materials, will probably be for people employed in factories producing carbon nanotube materials. See Nature Nanotechnology at references below.

In fact, nanotube technology is being investigated in the health field as a possible medical procedure to fight cancer. Another nanotechnology research article summarized that "single-walled carbon nanotubes can now effectively target tumors in mice, which suggests that nanotubes could form the basis of a safe drug-delivery system for cancer [treatment]".

In 2008, in a letter published in Nature Nanotechnology, Poland et als reported that "Carbon nanotubes introduced into the abdominal cavity of mice show asbestos-like pathogenicity in a pilot study".Quoting from the abstract of that article,

Carbon nanotubes have distinctive characteristics, but their needle-like fibre shape has been compared to asbestos, raising concerns that widespread use of carbon nanotubes may lead to mesothelioma, cancer of the lining of the lungs caused by exposure to asbestos.

Here we show that exposing the mesothelial lining of the body cavity of mice, as a surrogate for the mesothelial lining of the chest cavity, to long multiwalled carbon nanotubes results in asbestos-like, length-dependent, pathogenic behaviour.

This includes inflammation and the formation of lesions known as granulomas. This is of considerable importance, because research and business communities continue to invest heavily in carbon nanotubes for a wide range of products5 under the assumption that they are no more hazardous than graphite. Our results suggest the need for further research and great caution before introducing such products into the market if long-term harm is to be avoided. [16].

Risk of Potential Exposure to Nanotechnology, & Carbon Nanotube Particles or Process-related Chemicals

The potential for occupational exposure to engineered carbon-based nanomaterials in environmental laboratory studies was examined by David Johnson et als and reported in Environmental Health Perspectives in January 2010. The study concluded that

Engineered nanomaterials can become airborne when mixed in solution by sonication, especially when nanomaterials are functionalized or in water containing NOM. This finding indicates that laboratory workers may be at increased risk of exposure to engineered nanomaterials.

AIHA's The Synergist reported (May 2010) that in concert with the NIOSH Prevention through Design (PtD) green jobs (making jobs environmentally safe for workers who labor in the "green"-tagged industries). In the nanotechnology research and industrial field, hazards to workers appeared to be focused on "chemicals" used in research.

The emerging science of nanotechnology demonstrates the urgency for effective PtD design interventions that integrate OHS [Occupational Health & Safety] and environmental goals.

The article's authors, Heidel, et als, point out that while nanotechnology research has been conducted at Purdue University for many years, when the university was planning the Birk Nanotechnology Center (BNC) in West Lafayette, IN, a new state-of-the-art nanotechnology research facility for nanobiotechnology and nanomedicine, the facility design had to include steps to protect the safety and health of the workers as well as the surrounding community.

Safety measures designed to address potential hazards of chemical spills (a drop-down exhaust system) were included in the facility planning and design of the Birk Nanotechnology Center (BNC). Potential hazards associated with the production of ultra-small particles produced by some nanotechnology research or production were not cited in this magazine article.

Nanotechnology Guidance led by NIOSH - National Institute for Occupational Safety & Health

NIOSH reports via an upcoming conference on "Nanomaterials and Worker Health" (July 2010) its role in leading research on nanotechnology hazards and worker safety. Quoting from that document:

NIOSH is the leading federal agency conducting research and providing guidance on the occupational safety and health implications and applications of nanotechnology.

This research focuses NIOSH's scientific expertise, and its efforts, on answering the questions that are essential to understanding these implications and applications:

As observers generally agree, research to answer these questions is critical for maintaining U.S. competitiveness in the growing and dynamic nanotechnology market.

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