Toxicity of carbon nanotubes to humans and the environment

Carbon nanotubes (CNTs) are ideally described by the winding of a sheet of graphene (one of the layers superimposed to form graphite). Their small diameter (from 0.5 nm for the finest to several tens of nanometers for the widest) combined with their length, which can range from a micron to several centimeters in the most extreme cases, gives them a very high form factor and classifies them as one-dimensional nanomaterials. They may comprise one or more concentric tubes, in which case they are referred to as single-walled (or single-sheet) or multi-walled (or multi-sheet) CNTs.

Providing precise economic data on the production and use of CNT at industrial level is risky, since reliable sources are scarce and manufacturers' data are most often expressed in terms of production capacity, which can be very different from the quantities actually produced and marketed. Institutional inventories, such as the Woodraw Wilson Institute's , provide examples of products available on the market and declared to contain CNTs, or suspected of doing so. Numerous reports by industry consultants (who generally recycle the same data whose sources are neither disclosed nor verifiable) nevertheless describe a flourishing and constantly expanding market. In fact, CNTs are widely used in the energy (rechargeable batteries), composite materials (including the automotive sector) and paint industries. They are generally used in small proportions in these products, but their large-scale commercialization suggests that they will eventually be produced in significant tonnages. France has been a forerunner in this field, with the mandatory annual declaration of "the manufacture, import or production of substances in nanoparticulate form" since 2013, and the creation of the R-Nano database. , which gathers data from these declarations. Although the data in the database are protected by confidentiality agreements, an annual report, for example, has since made it possible to monitor trends in the production and use of nanomaterials in general. The question of health impact mainly concerns workers, who are in fact the only ones potentially exposed to CNT as manufactured. Indeed, once incorporated into consumer products, the risk of exposure to users is very low under normal conditions of use, since CNTs are encapsulated in matrices, or simply inaccessible to the user. To our knowledge, there are no applications currently on the market in which CNTs are in direct contact with humans, as could be...