So you want to make or use carbon nanotubes, but you are worried about handling then safely. What do you do? The good news is that the UK Health and Safety Executive has just published an information sheet that addresses just this question. Risk management of carbon nanotubes is (according to the blurb) “specifically about the manufacture and manipulation of carbon nanotubes, and has been prepared in response to emerging evidence about the toxicology of these materials.”
But is it any good? Here’s my initial take:
HSE recommends a precautionary approach for managing the risks of all carbon nanotubes. This is a good move. The evidence so far—which admittedly is sparse—points towards all forms of carbon nanotubes being more harmful in the lungs than non-nanotube forms of carbon. Of course, it depends on how you define “precautionary,” but “looking before you leap” seems a reasonable translation in this case.
No mention is made of possible exposure when working with carbon nanotube-containing products. HSE’s information sheet is clear that exposure to nanotubes can occur when making the stuff, when using it, and when researching its properties. But there is no mention of what could occur when machining, grinding or cutting a product containing carbon nanotubes. To be fair, research so far indicates that in most cases, once carbon nanotubes are embedded in a product they are unlikely to come out. But if a precautionary approach is to be taken, it seems sensible to at least ask whether there is a chance that exposure to the material will occur while working with carbon nanotube-containing products.
The review of new evidence neglects particle-like effects in the lungs. The information sheet revolves around concerns over asbestos-like behavior and certain types of carbon nanotubes, which is understandable given the unpleasantness and latency period of diseases like mesothelioma. But current research suggests that even clumps of carbon nanotubes that don’t look like asbestos fibers are more toxic if inhaled than might be imagined. Last July, Anna Shvedova and colleagues published research showing that inhaling non asbestos-like single walled carbon nanotubes at concentrations currently recommended as safe by many manufacturers could be harmful.
In other words, it isn’t just asbestos-like behavior that we need to be concerned with here.
Use of carbon nanotubes appears to be discouraged in the absence of information on inhalation hazards. The information sheet states:
“HSE views CNT’s [carbon nanotubes] as being substances of very high concern. Although the recent findings only apply to some CNTs we think a precautionary approach should be taken to the risk management of all CNTs, unless sound documented evidence is available on the hazards from breathing in CNTs. If their use cannot be avoided, HSE expects a high level of control to be used.”
I may be reading this section wrong, but the message seems to be: If you don’t have a good handle on how harmful the substance you are using might be, don’t use it. But if you absolutely must, do everything possible to reduce exposures to a minimum. As there are no definitive data on carbon nanotube toxicity yet, this advice seems to boil down to the use of carbon nanotubes being discouraged.
Given the economic potential here, I’m interested in how this will play with industry.
Recommended qualitative risk management actions will reduce exposures… At the heart of the information sheet is advice on steps to reduce exposure to airborne carbon nanotubes when working with the substance. These are solid, generic, good occupational hygiene practices—“use appropriate work processes,” “control exposures at source,” “make sure exposures are controlled at all times” etc. And if followed, they should lead to fewer people being exposed to less material. But I do wonder how practical some of them are for dealing with certain forms of carbon nanotubes—especially when it comes to working in fume cupboards and keeping material wet where possible.
…But there are few indications of “how much is enough.” Qualitative actions abound in the information sheet: “use appropriate work processes;” “provide suitable work equipment;” maintain “adequate control of exposure at all times.” But such advice is hard to apply in the absence of any information on what processes are “appropriate,” how suitability is determined, and when “adequate control” is achieved.
I’m sure the point here is that any actions to reduce exposures are better than none. But without quantitative benchmarks, the chances are that some people will be exposed to worryingly high levels of carbon nanotubes (under the “we tried our best” arguement), while others will struggle to obtain exposure levels that are needlessly low.
On balance, I have to commend the HSE on coming out with the information sheet on the ground that any information is better than no information, and I’m sure that some will find it helpful. But I do worry that the information provided isn’t specific enough to either protect peoples’ health effectively, or provide nanotech businesses with the help they need to do the right thing without over-doing it.
And unfortunately, the document fails to provide links to other sources of information that may help remove some of the ambiguity (see some of the documents below for instance).
The bottom line here is that the information sheet is great for raising awareness, but seems to falls short of providing much in the way of practical advice.
Of course, I don’t actually have to make hard decisions on what exposures are acceptable for my employees, which controls to put in place, and how to assess their effectiveness.
Maybe if I did, my perspective would be different.
End Notes
I should note that I was asked to informally review a late draft of the information sheet last year. I suspect I was too late in returning my comments though—the published document isn’t substantially different from my review copy.
For more substantive advice, I would recommend reading the document “Nanotechnologies – Part 2: Guide to safe handling and disposal of manufactured nanomaterials” from BSI Inc. My review of it can be found here.
More detailed information on working safely with nanomaterials is also published by the US National Institute for Occupational Safety and Health.
Similar advice is available from the standards organizations ISO and ASTM International (see Alphabet soup hides the secrets of safe nanotech! for further information)
Thoughts on applying Control Banding to working with nanomaterials can be found in this excellent paper by Sam Paik and colleagues. While not dealing specifically with carbon nanotubes, it does develop a framework for making exposure control decisions:
Paik’s work forms the basis of safe handling guidelines recommended by the Institut de recherche Robert-Sauvé en santé et en sécurité du travail (IRSST), the Commission de la santé et de la sécurité du travail (CSST) and NanoQuébec.
Additional 2020 Science blogs addressing carbon nanotube safety:
- Carbon nanotubes: the new asbestos? Not if we act fast
- Resolving the carbon nanotube identity crisis
- Asbestos-like nanomaterials – should we be concerned?