Fraunhofer Institute for Toxicology and Experimental Medicine
The toxicological characterization of new materials is a key tool for assessing their hazard potential. In a two-year intraperitoneal study, the carcinogenic potential of various fibrous carbon materials was investigated at doses of up to 1 × 10⁹ WHO fibers. The materials tested included:
- four types of multiwalled carbon nanotubes (MWCNT) with diameters ranging from 10 to 30 nm,
- single-walled carbon nanotubes (SWCNT) with diameters <10 nm,
- as well as respirable fragments of a pitch-based carbon fiber.
The aim of the study was to evaluate a potential asbestos-like mode of action, particularly in relation to fiber rigidity as well as diameter and length distribution. Fiber rigidity describes the stiffness of a fiber – how easily or difficult it is to bend. Stable, rigid fibers (high rigidity) can cause greater mechanical tissue damage, whereas flexible fibers (low rigidity) are more likely to twist or form bundles, which may reduce their pathogenic impact.
Mesotheliomas occurred in all test groups; however, the incidence was predominantly low to very low. The highest incidence was observed with rigid, pitch-based carbon fiber fragments with microscale diameters. For nanoscale MWCNT, the data suggest a possible critical diameter threshold between 20 and 30 nm, below which no carcinogenic effect is expected. Despite their extremely small individual fiber diameters and resulting high flexibility, SWCNT showed a low but potentially relevant hazard, which may be attributable to the formation of fiber bundles.
The findings support the assumption that fiber rigidity – largely determined by diameter – is a key predictor of the pathogenicity of fibrous carbon materials.
