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Grouping all carbon nanotubes into a single substance category is scientifically unjustified

Nature Nanotechnology volume 15, page 164 (2020)Cite this article

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To the Editor — The International Chemical Secretariat (ChemSec) recently added carbon nanotubes (CNTs) to the so-called SIN (‘Substitute It Now’) list of chemicals that they believe should be restricted or banned in the EU1. CNTs are the first nanomaterials to be placed on the SIN list. Should this ‘designation’ concern us as scientists active in the areas of nanotoxicology and nanomedicine? Yes, as it implies that all CNTs can be considered as one material category, which is not the case. Grouping or categorization of chemicals is a valid approach in risk assessment provided that substances with similar properties are grouped together2. However, the key (scientific) question is whether all CNTs display the same properties.

Five years ago, the International Agency for Research on Cancer (IARC) classified a particular type of long and rigid CNT, designated as MWCNT-7, as possibly carcinogenic to humans on the basis of available animal studies, whereas all other CNTs were considered ‘not classifiable’ with regard to their carcinogenicity3. The findings of the original evaluation on the inadequate or limited evidence of carcinogenicity for most CNTs were confirmed in a thorough follow-up study a few years later4. Hence, while there is no doubt that long and rigid CNTs may cause considerable damage to the lungs following pulmonary exposure (especially when administered at high doses5), it is important to note that short and/or tangled CNTs are much less harmful6,7. Indeed, it has been demonstrated that the ‘asbestos-like’ pathogenicity of long CNTs can be alleviated through chemical functionalization, possibly as a result of the effective shortening of the CNTs through debundling or untangling8. Chemical functionalization may also impact the stiffness of CNTs, which is perhaps one of the most important parameters with regard to biological reactivity9.

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Authors and Affiliations

  1. Institute of Environmental Medicine, Karolinska Institutet, Stockholm, Sweden

    Bengt Fadeel

  2. University of Manchester, Manchester, UK

    Kostas Kostarelos

  3. Catalan Institute of Nanoscience and Nanotechnology (ICN2), Barcelona, Spain

    Kostas Kostarelos

Authors
  1. Bengt Fadeel
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  2. Kostas Kostarelos
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Correspondence to Bengt Fadeel.

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Fadeel, B., Kostarelos, K. Grouping all carbon nanotubes into a single substance category is scientifically unjustified. Nat. Nanotechnol. 15, 164 (2020). https://doi.org/10.1038/s41565-020-0654-0

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