Navigating the Promise and Peril of Carbon Nanotubes
The building blocks of tomorrow's technology, carbon nanotubes, hold a hidden challenge we are just beginning to understand.
Imagine a material stronger than steel, lighter than aluminum, and more conductive than copper, all while being thinner than a human hair. This is the reality of carbon nanotubes (CNTs), a revolutionary nanomaterial shaping everything from our electronics to our medicine. Yet, as with many powerful innovations, they come with a potential shadow side. A growing body of scientific evidence suggests that if these microscopic tubes enter our bodies, they could pose significant health risks, mirroring the path of once-lauded materials like asbestos. This article explores the incredible potential of carbon nanotubes and the critical precautions we must take to safely harness their power.
To understand the risks, we must first grasp what carbon nanotubes are. Think of a sheet of carbon atoms, like chicken wire, rolled into an impossibly tiny cylinder. These are carbon nanotubes. They can be single-walled (SWCNTs), just one atom in thickness, or multi-walled (MWCNTs), consisting of multiple concentric tubes3 .
Their unique properties are what make them so desirable:
These properties have led to their use in a vast array of applications, from improving batteries and capacitors to serving as carriers for anticancer drugs in biomedicine3 4 .
Carbon nanotubes are thousands of times thinner than a human hair1 .
The very properties that make CNTs so useful—their small size, large surface area, and persistence—are also what raise health and safety concerns1 . When inhaled, these tiny, fiber-like particles can behave in ways that are alarmingly familiar to toxicologists.
The primary concern revolves around what happens when CNTs are inhaled, making occupational settings a key focus. Workers involved in the production, handling, or processing of these materials are at the highest potential risk7 .
Research has revealed that certain types of CNTs share troubling characteristics with asbestos fibers3 8 . Both are biopersistent, meaning they can remain in the body for long periods without breaking down. Their needle-like shape allows them to penetrate deep into the lungs and even reach the pleural cavity, the space surrounding the lungs8 .
Once there, stiff and rigid CNTs are particularly dangerous. As Professor Hiroyuki Tsuda's research group explains, "Rigid MWCNTs are not readily phagocytosed [engulfed by immune cells], remain in the pleural cavity, and induce chronic inflammation and genotoxicity"8 . This prolonged inflammation and damage to DNA is a known pathway to cancer.
Animal studies have shown that exposure to specific types of multi-walled CNTs, like MWCNT-7, can lead to mesothelioma, the same cancer of the lung lining caused by asbestos exposure3 . The U.S. National Institute for Occupational Safety and Health (NIOSH) has reported that in rodent studies, CNTs have caused adverse lung effects, including pulmonary inflammation and rapidly developing, persistent fibrosis (scarring)7 .
| Characteristic | CNTs | Asbestos |
|---|---|---|
| Shape | Needle-like fibers | Needle-like fibers |
| Biopersistence | High | High |
| Lung Penetration | Deep penetration | Deep penetration |
| Health Effects | Mesothelioma, fibrosis | Mesothelioma, fibrosis |
For years, scientists hoped that thinner, more flexible CNTs would be safer. However, a compelling 2025 review study led by Professor Hiroyuki Tsuda challenged this assumption.
| CNT Type | Behavior in Pleural Cavity | Behavior in Lung | Carcinogenic Outcome |
|---|---|---|---|
| Thick & Rigid | Resists cleanup, causes chronic inflammation and DNA damage8 . | Interacts with immune cells, induces inflammation and tissue damage8 . | Strong evidence of mesothelioma and lung cancer3 8 . |
| Thin & Flexible | May be cleared more easily8 . | If not cleared, causes cycles of inflammation and damage8 . | Evidence of tumor development in long-term lung studies8 . |
The identification of these hazards is not a call to ban a valuable technology, but rather the essential first step in learning to use it safely. As the researchers note, many toxic compounds, like formaldehyde, are used routinely under strict safety regulations8 .
Using enclosure or confinement of operations and effective ventilation to prevent airborne release7 9 .
Using respirators with a high level of protection where exposure cannot be controlled by other means9 .
Because inhalation is the main exposure route, occupational safety is paramount. NIOSH has recommended a exposure limit (REL) of 1 μg/m³ of elemental carbon for carbon nanotubes and nanofibers, measured as an 8-hour time-weighted average7 . This level is intended to reduce the risk of lung inflammation and fibrosis.
To achieve this, a multi-pronged approach is required:
| Tool/Reagent | Function | Example in Action |
|---|---|---|
| Chemical Vapor Deposition (CVD) | A common synthesis method for CNTs using high temperatures and carbon-containing gases4 . | Used in industrial production of CNTs; requires management of toxic byproducts4 . |
| Reference Materials (RMs) | Standardized, well-characterized CNT samples from sources like NIST5 . | Allows researchers and industries to calibrate instruments and compare toxicity data reliably5 . |
| PEG (Polyethylene Glycol) | A polymer used to coat CNTs, improving their solubility and biocompatibility3 . | Used in drug delivery systems to help CNTs circulate longer in the bloodstream without being rejected3 . |
| Enzymatic Biodegradation | Using oxidative enzymes from bacteria to break down CNTs. | Being explored as a natural route to remediate CNT contamination in the environment. |
| High-Efficiency Particulate Air (HEPA) Filtration | A method for physically removing CNT particles from the air4 . | A key engineering control in workplaces to protect workers from inhalation exposure7 . |
Globally, governments are taking action. In the U.S., the Environmental Protection Agency (EPA) regulates CNTs under the Toxic Substances Control Act (TSCA), requiring premanufacture notifications and controlling new uses through Significant New Use Rules (SNURs)1 9 . These rules mandate strict workplace practices, disposal methods, and limits on environmental release9 .
The environment is another area of focus. CNTs can enter ecosystems through wastewater or improper disposal. Studies show they can affect aquatic organisms and soil microbial communities4 . Promising research, like the DECANO project in France, is investigating how bacteria and their enzymes can be used to biodegrade CNTs, offering a future bioremediation solution.
| Domain | Potential Hazard | Mitigation Strategy |
|---|---|---|
| Workplace | Inhalation leading to lung disease and cancer7 . | Enclosure, ventilation, respirators, and medical surveillance7 9 . |
| Environment | Accumulation in water and soil, toxicity to organisms4 . | Advanced filtration of wastewater, strict disposal regulations, and development of bioremediation4 . |
| Consumer Products | Uncontrolled release during product life cycle4 . | Embedding CNTs in solid polymer matrices to prevent release, and life-cycle assessments9 . |
Carbon nanotubes exemplify the classic dual-use technology: offering immense benefits while demanding profound responsibility. The scientific community, regulatory bodies, and industry are now acutely aware of the potential threats. The path forward does not lie in fear, but in informed vigilance and rigorous safety culture. By continuing to research their effects, implementing and enforcing protective regulations, and designing safer alternatives, we can unlock the transformative potential of carbon nanotubes while ensuring that their hidden dangers remain firmly under our control.