Risks associated with carbon nanotubes

Because of their sometimes long, fibrous form, reminiscent of asbestos, carbon nanotubes raised strong concerns about their toxicity very early on.

The long multi-walled carbon nanotubes (NTCs) classified as carcinogens

In 2017, the International Agency for Research on Cancer (IARC) classified one of these nanotubes, Mitsui-7, as a ‘possible human carcinogen’ (2B). After many years, and a last consultation during the summer of 2021, the European Chemicals Agency (ECHA) validated in March 2022 the classification as carcinogenic by inhalation (cat. 1B) of long multiwall carbon (nano)tubes . This includes those with a diameter ≥ 30 nm and < 3 μm, a length ≥ 5 μm and a width to height ratio > 3:1¹Cf. Echa’s Rac agrees to carcinogenic classification for multi-walled carbon tubes, Chemical Watch, March 23, 2022 . . This classification follows the submission of a dossier by Germany for the inclusion of the substance in Annex VI of the CLP Regulation.

Attention, short ones can also be toxic

In 2023, contrary to the initial belief that only long and thick multi-walled carbon nanotubes (NTCs) pose a problem, an in-depth study by the French National Institute for Research and Safety (INRS) reveals that short and thin NTCs, like their long and thick counterparts, induce acute pulmonary inflammation. Additionally, for short and thin NTCs, chronic inflammation and hyperplasia were observed, which are not observed for long and thick NTCs. This study is based on in vivo and in vitro experiments and has been the subject of a doctoral thesis²Cf. Hélène Barthel, Influence of physical parameters of multiwall carbon nanotubes on their toxicological properties in a bronchial epithelial cell model: reconciliation with pulmonary effects in rats, PhD Thesis, 2022 and two scientific articles³Barthel et al, Needlelike, short and thin multi-walled carbon nanotubes: comparison of effects on wild type and p53+/- rat lungs, Nanotoxicology, 2023 and Barthel et al, Continuous Long-Term Exposure to Low Concentrations of MWCNTs Induces an Epithelial-Mesenchymal Transition in BEAS-2B Cells, Nanomaterials 2021.

A look back at previous episodes

In May 2014, the French Health Security Agency (ANSES) recommended a classification of carbon nanotubes as hazardous substances so that measures could be put in place to restrict their use or even ban their use in certain consumer applications.

In 2015, the Société pour l’étude, la protection et l’aménagement de la nature dans le Sud-Ouest (SEPANSO) issued an alert on the risks linked to the production of carbon nanotubes by Arkema in Mont (Pyrénées-Atlantiques) and asked for production to be stopped until the harmlessness of nanos could be established for employees, consumers and the environment⁴Cf. Mont: carbon nanotubes in the crosshairs of the Sepanso, La République des Pyrénées, February 25, 2015; see also ANSES, Avis relatif à “l’évaluation des risques liés au GRAPHISTRENGTH C100 réalisée dans le cadre du programme Genesis”, November 28, 2013.

In November 2019, carbon nanotubes are the first nanomaterials to be integrated into the SinList, a list of substances to be replaced urgently because deemed too dangerous⁵Cf. With its SinList, the NGO ChemSec alerts a non-expert public to chemical risks, Novethic, November 2019 and New chemicals on the SIN List challenge the global supply chain, ChemSec, November 2019.

The same month, the European Agency for Safety and Health at Work awarded the 2018-2019 Healthy Workplaces Good Practice Award to Atlas Copco Industrial Technique, a Swedish manufacturing company that has taken a precautionary approach to minimizing worker exposure to carbon nanotubes⁶Cf. Sweden: protecting workers from potentially hazardous carbon nanotubes in manufacturing, OSHA Europe, November 2, 2019.

In July 2020, ECHA published an assessment report on multiwall carbon nanotubes (MWCNTs: a tube-shaped and entangled synthetic graphite) conducted by the German Institute for Occupational Safety and Health (BAuA)⁷Cf. SUBSTANCE EVALUATION CONCLUSION as required by REACH Article 48 and EVALUATION REPORT for Multi-walled Carbon Nanotubes (MWCNT), synthetic graphite in tubular shape and tangled, BAuA / ECHA, July 2020. The report pointed out that the information required by 1 January 2020 under REACH had not yet been (sufficiently) filled in by registrants and that additional measures were therefore necessary, starting with a compliance check. Once the data required by REACH is provided by companies, ECHA may decide whether additional information would be needed. ECHA was urging registrants to update their dossiers and/or develop testing proposals to comply with REACH requirements.

In the United States, the U.S. Environmental Protection Agency (EPA) has issued several Significant New Use Regulations (SNURs) for carbon nanotubes, requiring anyone wishing, for commercial purposes, to manufacture, import, or process these carbon nanotubes to notify the EPA at least 90 days before. 2 of these SNURs are:

• one in 2020, concerning free PMN P-15-54 (i.e. not included in a matrix)⁸Cf. Significant New Use Rules on Certain Chemical Substances (20-1.5e) – § 721.11467Carbon nanotubes (generic), EPA, September 17, 2020, which came into force on November 16, 2020
• one in 2021, concerning PMN P-18-182 multiwalled⁹Cf. Significant New Use Rules on Certain Chemical Substances § 721.11361 Multiwalled carbon nanotubes (generic), EPA, 18 August 2021

In 2021, carbon nanotubes have been identified as one of the four most risky categories of nanomaterials by a team from University College Dublin¹⁰Cf. A semiquantitative risk ranking of potential human exposure to engineered nanoparticles (ENPs) in Europe, Li, Y and Cummins, E, Science of the Total Environment, 778, July 2021.

Explore the bibliography below to learn more.