Cellulose nanofiber (CNF) is a promising new material used in a wide range of industries. The application of soda-anthraquinone cooking of sugi (Japanese cedar) and subsequent nanofibrillation of the enzymatically treated pulp by wet milling enabled us to establish a simple integrated manufacturing process to obtain sugi-CNFs. However, there are concerns that the sugi CNF might be mutagenic or cause skin irritations;therefore, we tested these hypotheses. Acute oral toxicity test using mice

more »

... d no abnormality, with an LD 50 value of over 2,000 mg/kg. Also, the sugi CNF was found to be non-mutagenic in the bacterial reverse mutation test. In addition, no anomalies were detected in the in vitro chromosomal aberration test using Chinese hamster lung fibroblast cells. Moreover, the CNF treatment of rabbits in dermal irritation or corrosion tests did not produce severe dermal irritation or corrosion or distinctive signs of toxicity. Erythema was observed in the site of 5wt% CNF application in all the tested animals one hour after the CNF application ended;however, erythema disappeared by the 48th hour. As a result, the sugi CNF was evaluated to be in the non-irritating category. According to the results from the guinea-pig maximization test, which predicts skin sensitization, the effect of the sugi CNF was classified as the weakest grade. In conclusion, the sugi CNF is unlikely to cause mutagenicity in organisms. In addition, the level of skin irritation caused by the sugi CNF is within the normal range of handling.