Some researchers have criticised ChemSec for putting carbon nanotubes on the SIN List; here’s our response
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Some researchers have criticised ChemSec for putting carbon nanotubes on the SIN List; here’s our response

Late last year ChemSec added carbon nanotubes to the SIN List, thereby suggesting that nanomaterials should be identified as Substances of Very High Concern (SVHCs) for the first time.

After having described our methodology behind this move in the scientific journal “Nature Nanotechnology”, two critical opinion pieces and one editorial appeared in the next volume.

The title of the editorial – The risks of nanomaterial risk assessment – itself reveals that the critique is based on a misunderstanding, which in its defense, is a common and frequent misunderstanding.

The SIN List, like its blueprint the REACH Candidate List, adds substances based solely on their intrinsic properties. It is hazard-based, and thus no risk assessment has been performed.

A hazard-based system, which starts with identifying chemicals based on their intrinsic properties, is what ChemSec, and many other stakeholders, consider to be a modern and progressive chemicals management framework.

The idea is that SVHCs should be substituted wherever possible, as they are by definition very hazardous.

“The critique is based on a misunderstanding, which in its defense, is a common and frequent misunderstanding”

But for specific important applications there may be justification for their continued use until alternatives are available. It is therefore an urgent priority, during this so-called authorisation process, that a thorough risk assessment is carried out to ensure that such uses are minimised. (ChemSec has written extensively about the relation between hazard and risk in chemicals management in the past, for example here.)

There were also other important comments regarding our decision to group all carbon nanotubes into one entry on the SIN List.

There are many types of carbon nanotubes. They can be single-walled, double-walled, multiwalled, long, short or tangled. The difficulty with characterisation and identifying what is “one” nanomaterial is very challenging from a regulatory perspective. Studies of hazardous properties are conducted on one specific form, possibly even from a specific production batch. Can we use that data to say anything about other forms?

In the case of carcinogenicity, which is an important reason for the SIN Listing, evidence of carcinogenicity exists for some forms of multiwalled carbon nanotubes. But in addition to this, for a number of other forms, evidence of lung inflammation and other mechanisms associated with cancer exist.

Shifting the perspective, we could not find good reason to exclude any form from being a suspected carcinogen. Environmental persistence seems to be shared by all forms, while toxicity for reproduction has mainly been seen for single-walled carbon nanotubes.

There is a strong political trend that acknowledges the need to move from regulation substance-by-substance to a group approach. A recent example is PFAS, which include almost 5,000 substances. So far, the regulation of one of them has led to increased use of another. We do not want to go the same way with the different forms of carbon nanotubes.

And here’s a reality check which tells us that grouping all carbon nanotubes into one entry is very relevant: in large-scale industrial production and use of carbon nanotubes, we rarely see products purified into 100% of a specific carbon nanotube type; there is always a mix.

It is also this large-scale production we hope that a SIN Listing of carbon nanotubes will help to scrutinise, so that the production and use of carbon nanotubes can become more specific and safer, and they are only used when needed and after proper risk assessment. From this perspective we do in fact believe that SIN Listing might spur innovation of nanotechnology.

You can read our full response to the critique in Nature Nanotechnology in the same scientific journal here. It is written together with assistant professor Steffen Foss Hansen from DTU, who coordinated the scientific work behind the SIN Listing of carbon nanotubes.