Up to now carbon nanotubes (CNTs) are not added to foods or to cosmetic products. Therefore it is their uptake via the lung into the body that needs to be investigated more closely. Hence, it is not surprising that several biological studies have been carried out on rats and mice to find out more about that path of uptake. Studies on mice have shown that carbon nanotubes can penetrate through to the deepest regions of the lung.
Mainly cosmetic or pharmaceutical products, for example suncreams, are concerned when discussing the uptake of nanoparticles via the skin. Since no comparable applications are known or projected for carbon nanotubes (CNTs), their direct contact with the skin is quite improbable at present or may be rather due to accidents or improper application.
For the time being, carbon nanotubes (CNTs) are not applied to foods. Only in theory, they can be transported into the gastrointestinal tract through unwanted hand-to-mouth transfer or when swallowing particles which are transported through cleaning processes from the respiratory tract into the esophagus. As a rule, particles that have been taken up via the food are excreted via the stool. No proof has been furnished as yet that carbon nanotubes get into the intestines and are taken up from there into the body.
The term "carbon nanotubes" (CNTs) comprises a group of carbon-containing nanomaterials with diverse properties, which for example differ in their surface structure or in the number of walls. These features significantly affect the strength of the toxic effects of the CNTs. Many of the observed effects are due to the fibre-like form of the carbon nanotubes, which may cause indirect effects upon contact with the surface of the environmental organisms. Universally valid statements about the environmental toxicity of carbon nanotubes are not yet possible.