[Research] Improving knowledge about the health effects of carbon nanotubes
INRS conducted a study to improve knowledge about the potential toxicity of multi-walled carbon nanotubes, one of which is already classified by IARC as “possibly carcinogenic to humans”. The work aimed to evaluate the influence of the diameter and length of nanotubes on health, and therefore to reinforce the prevention of hazards in the event of inhalation by staff that are required to produce or handle them.
© G. Kerbaol / INRS / 2023
In this age of nanotechnology, the use of multi-walled carbon nanotubes (MWCNTs) is very common in industry. In fact, there has been a growth in the use of the physical and chemical properties of these carbon nanotubes (CNTs) for different applications :
- electrical (conduction, resistance),
- thermal (high temperature stability),
- chemical (adsorption capacity).
Health effects on employees
Employee exposure by inhalation during production, use or handling of MWCNTs raises questions concerning their potential health effects on employees.
The physical and chemical properties of these materials, as well as their biopersistence are of concern because of their toxic effects. Given their physical properties, they can easily reach the lower respiratory tract and deposit on the pulmonary epithelium.
In 2017, the International Agency for Research on Cancer (IARC) classified a carbon nanotube, the Mitsui-7 (MWNT-7), as “possibly carcinogenic to humans” (2B) and the Risk Assessment Committee of the European Chemicals Agency is considering categorising all MWCNTs whose dimensions correspond to the World Health Organisation’s definition [length (L) ≥ 5 µm, diameter (D) ≤ 3 µm and an L/D ratio of ≥ 3] as presumed carcinogens (1B).
However, some nanotubes do not correspond to these criteria. For such nanotubes, there is still a lack of data concerning their toxicity. For this reason, INRS’s toxicology teams carry out studies to improve knowledge about the health effects of a whole range of nanotubes.
Faced with the lack of knowledge about the toxicity of different CNTs whose shapes (length and diameter) may vary, INRS finalised a study on the relevance of in vitro and in vivo tests to evaluate the ability of CNTs to cause cancer. The goal was to help to determine the presence of health risks for workers exposed to carbon nanotubes of various sizes.
A large portion of work concerned in vitro tests (on cells). These tests alone can provide information about the toxicity of a great variety of MWCNTs based on their length and thickness. Therefore, a test was developed with human bronchial epithelial cells. It analyses the induction of the epithelial–mesenchymal transition (EMT) by MWCNTs, a process involved in the development of fibrosis or the dissemination of cancer cells in the body. Experiments show that long and thick CNTs caused this transition early and at lower concentrations than short and thin CNTs. In addition, even though it was shown that the effects caused by CNTs were reversible after the end of exposure, the reversion is not complete and could contribute to a sensitisation of cells.
To complete this work, in vivo tests were also performed. Genetically modified rats, whose strain is likely to develop cancer more quickly, were exposed to long and thick MWCNTs and short and thin MWCNTs. Experiments showed that both types of MWCNTs caused acute pulmonary inflammation and exposure to short and thin MWCNTs caused chronic inflammation and hyperplasia.
This study provided additional information about the carcinogenic potential of short and thin CNTs, which are not included in the classification proposal submitted to ECHA.
The findings appear to indicate that it is relevant to not categorise CNTs differently based on their size, and that it is necessary to handle short and thin CNTs with as much precaution as the long and thick ones. The effects of CNTs must be carefully evaluated regardless of their morphology.
Pending ECHA’s work, companies should implement a chemical risk assessment approach based on the general principles of prevention. This involves, in particular, the identification of the hazardous products present in the company, irrespective of its activity, and an exhaustive and rigorous assessment of risks. Furthermore, regulations require specific provisions for hazardous chemicals, carcinogenic, mutagenic and reprotoxic (CMR) substances and carcinogenic processes.
This study was done within the framework of a PhD thesis in 2022.
A presentation made during the convention of the French Society for cellular and molecular toxicology received the prize for best oral communication.
Hosting of doctoral candidates
Every year, about 30 doctoral students co-supervised by INRS study leaders and academics are involved in studies.
This co-supervision promotes the establishment of links with partner universities, encouraging mutual scientific enrichment and a pooling of resources to further knowledge. These PhD students, and through them the collaborations undertaken, contribute significantly to INRS’s scientific production.
Out of the roughly 100 studies conducted each year, more than a third are the subject of a thesis.
For more information
Scientific article on in vitro data :
- Nanomaterials | Free Full-Text | Continuous Long-Term Exposure to Low Concentrations of MWCNTs Induces an Epithelial-Mesenchymal Transition in BEAS-2B Cells (mdpi.com)
Scientific article on data from in vivo experiments :