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Carbon Nanotubes – First nanomaterial of high concern on the SIN List

3d model of a carbon nanotube

 

Since 2008, ChemSec has aimed at both guiding companies and catalyzing the EU REACH legal process, by listing hazardous chemicals that in our view fulfil the legal criteria for being substances of very high concern (SVHCs), ahead of the official process. This list is called the SIN List, an intentionally chosen abbreviation that spelled out means “Substitute It Now”.


High-tech material or a threat of incalculable proportions?

Ever since the start of the SIN List there have been requests to add nanomaterials to the SIN List. To many companies, NGOs and even regulators, “nano” is something very diffuse. Some see it as very futuristic, high-tech and a potential solution to most problems. Others see it as a main threat of incalculable proportions. Politically and legally, the main discussions so far have been about definitions and characterisations, not providing any clarity about safety.

So, when we found the scientific evidence to make a case and put a nanomaterial – Carbon Nanotubes – on the SIN List, we revisited the thought of “doing something about nano” in 2019.

Carbon nanotubes are, as the name suggests, thin carbon sheets rolled into tubes. The tubes can be longer or shorter, have one or several walls and they can be tangled. As is often the case for nanomaterials, characterisation of carbon nanotubes and where to draw the line between different forms can be difficult. The difficulty in characterization is problematic also when investigating hazardous properties.


Carcinogenicity and reprotoxic effects

Carbon nanotubes have been seen as a high-tech new material with much potetial. So far, consumer applications have been mainly about making lightweight material strong such as sportsequipment and also superblack coatings.

Several studies of different types of multiwalled carbon nanotubes show carcinogenicity for lungs and one type was classified as “possibly carcinogenic to humans” by the International Agency for Research of Cancer, IARC, this summer. Genotoxicity and lung damage have been shown by more types of carbon nanotubes, including single walled, double walled and multiwalled.

The persistence of carbon nanotubes under realistic conditions has been proven. And for single walled ones, there is evidence of reprotoxic effects.


Drawing the line between hazardous and less hazardous

There were many discussions internally, as well as with experts, before deciding to place all carbon nanotubes as one entry on the SIN List. There were several reasons for this decision: practical, political and scientific.

Purifying carbon nanotubes is so far technically challenging and costly, meaning that in practice, products, such as badminton rackets or coatings often consist of several types of carbon nanotubes.

We are also striving politically towards a more groupwise regulation of chemicals, as the chemical-by-chemical assessment has proven to be very ineffective and also risks resulting in regrettable substitution.

And perhaps most importantly: scientifically we could not justify where to draw a line between hazardous and less hazardous carbon nanotubes.


Evaluated as any other chemical substance

ChemSec SIN List logoWith this addition we want to show that nanoforms can and should be evaluated as any other chemical substance. Not all nanomaterials are safe, not all are hazardous, but it must be a case-by-case assessment. It is nothing “magical” or special with nano in this sense. It is important to remember that the toxicity of nanoforms can differ a lot from the other forms of a chemical.

We hope that the placing of carbon nanotubes on the SIN List will promote better control and more information about nanomaterials in general, as well as carbon nanotubes specifically.
 

Further reading

Dr Anna Lennquist

Anna Lennquist, Senior Toxicologist - International Chemical Secretariat (ChemSec)

My work at ChemSec focuses on substitution of hazardous chemicals. I am project manager for the SIN List, which has proven to be an important driver for innovation and a discussion base wherever chemicals policy is being developed. I am engaged in a number of different expert groups and stakeholder committees around the globe, aiming to speed up the transition to safer alternatives.

ChemSec is an independent non-profit organisation that advocates for substitution of toxic chemicals to safer alternatives.

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Rolf Packroff
There is a well-founded hypothesis that the classic 3-D principle (dose, dimension, durability) for the carcinogenicity of respirable fibres must be extended by the factor of rigidity. For carbon nanotubes, this results in a lower limit of the critical fiber diameter in the order of approx. 30 nm, below which a fiber no longer exhibits fiber-specific toxicity but behaves more like a granular, biopersistant particle with low toxicity. This is currently being experimentally verified in a research project of the Federal Institute for Occupational Safety and Health.
(https://www.baua.de/EN/Tasks/Res­earch/Research-projects/f2380.html).
20/07/20 13:12