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Understanding the Health Effects of Carbon Nanotubes

Ensuring safety for workers and users of emerging, high-tech nanomaterials


To measure the physical properties of carbon nanoparticles to support research into their toxic effects


We used specialized microscopic techniques and other chemical analyses to measure the purity and physical and chemical properties of different types of carbon nanotubes.


Our results supported toxicity studies by the National Toxicology Program to assess human health risks of occupational exposure to this class of chemicals. The studies also allowed NIH’s partner institutions to promote the adoption of exposure controls for the safe and successful introduction of CNT-based products to the market.

Nanomaterials are materials that are smaller than 100 nanometers wide. They have unique physical and chemical properties that distinguish them from the pure chemicals, allowing them to be used in applications ranging from advanced electronics to household cleaners to food packaging. Despite the widespread use of nanomaterials, their health and safety effects have not yet been thoroughly investigated.

Carbon nanotubes (CNT) are produced with a range of dimensions and are used in high-durability materials for biomedical products, air & water filtration, solar cells, supercapacitors, batteries, environmental remediation, thermal management, electrical cables and wires, and fibers and fabrics. Due to the huge number of applications, CNT production is poised to expand. According to statista.com, the worldwide market for carbon nanotubes was valued at around $4.5 billion in 2018 and has been predicted to triple by 2026.

This rapid market growth can be expected to result in greater environmental release of CNTs and a greater risk of human exposure to the material. Aerosol from manufacturing facilities carries CNTs that may end up in rivers, streams, and the air. Beyond the concerns around environmental and human health, there are questions around proper measures needed to protect workers at the facilities that produce the nanomaterials, who are most closely exposed to the material during production activities.

Very little is known about the effects of exposure to nanomaterials on human health. Some studies have suggested that exposure to CNTs may cause human and environmental health effects.

The National Toxicology Program at the National Institute of Environmental Health Sciences (NIEHS) is working with the National Institute of Occupational Safety and Health (NIOSH) to fill gaps in our knowledge of the health effects of CNTs. These agencies, together with RTI, are investigating CNT materials to understand their properties and establish best practices for worker respiratory protection.

RTI’s analytical laboratories analyzed the purity, composition, and dimensions of different types of carbon nanotubes for use in NTP’s studies. We used several instrumental techniques to measure the properties of the CNTs, information that would be essential for proper study design and interpretation of the results of animal studies.

Studies in rats showed that inhalation of CNTs can cause mutations in lung cells that could potentially lead to cancer. However, more work is needed to better understand how these CNTs cause mutations. The National Toxicology Program elected to study several types of CNTs to understand these health effects and to help NIOSH establish best practices for worker respiratory protection. In addition to measuring the properties of the materials, our characterization data indicated that CNTs can contain metal impurities like nickel, a known carcinogen. Impurities such as this could remain on the surface of the nanotubes and influence their toxicity.

The results provided by RTI helped NTP to conduct their toxicity studies and helped NIOSH to design recommendations and training programs on appropriate exposure controls for workers in the production of CNT-based products in 2018. The experience of this project also served as part of RTI’s growing research emphasis on the human health effects of nanomaterials. Through collaborations with our toxicology laboratories, risk assessment group, and analytical laboratory, RTI has established a vibrant research program devoted to protecting users and promoting the safe application of nanomaterials in the market.