Carcinogenicity assessment: "modern toxicology" considerations from experience in the evaluation of a carbon nanotube.

The novel properties and functions of nanomaterials have naturally alerted toxicologists to the fact that such materials may also have novel effects on the human body and other living organisms. In particular, materials with high stability or biopersistency have been shown to have a tendency to accumulate in the body, leading to chronic toxicity including carcinogenicity. However, in the early stages of toxicity research, the information is often limited to the effects of short-term exposure studies, and findings on chronic effects are very much delayed. In this context, it was exceptional that studies on multi-walled carbon nanotubes (MWCNTs) have started with the verification of their potential to induce mesothelioma. This toxicological endpoint was expected on the basis of existing knowledge of asbestos and asbestos-like fiber particles. This movement has led to the achievement of the original mission of "modern toxicology," which is "to achieve a win-win situation where both industrial promotion and safety assurance are ensured by communicating and sharing toxicity information to developers and consumers at a stage before mass production and consumption begins, that is, before massive exposure of the general public begins." Inaccurate toxicity assessments of asbestos in the 1980s and 1990s allowed its spread to our living environment, which is difficult to decontaminate, and the damage continues to this day. However, the case described here could be an example of realizing the proposition that "nanomaterials, the flagship of high technology, must not repeat the same mistakes."