Lung carcinogenicity by whole body inhalation exposure to Anatase-type Nano-titanium Dioxide in rats

To investigate the carcinogenicity of anatase-type nano-titanium dioxide (aNTiO₂), F344/DuCrlCrlj rats were exposed to aNTiO₂ aerosol at concentrations of 0, 0.5, 2, and 8 mg/m³. The rats were divided into 2 groups: carcinogenicity study groups were exposed for two years, and satellite study groups were exposed for one year followed by recovery for 1 day, 26 weeks, and 52 weeks after the end of exposure. In the carcinogenicity groups, bronchiolo-alveolar carcinomas were observed in two 8 mg/m³-exposed males, showing an increasing trend by Peto's test. However, this incidence was at the upper limit of JBRC's historical control data. Bronchiolo-alveolar adenomas were observed in 1, 2, 3, and 4 rats of the 0, 0.5, 2, and 8 mg/m³-exposed females and were not statistically significant. However, the incidence in the 8 mg/m³-exposed females exceeded JBRC's historical control data. Therefore, we conclude there is equivocal evidence for the carcinogenicity of aNTiO₂ in rats. No lung tumors were observed in the satellite groups. Particle-induced non-neoplastic lesions (alveolar epithelial hyperplasia and focal fibrosis) were observed in exposed males and females in both the carcinogenicity and satellite groups. Increased lung weight and neutrophils of bronchoalveolar lavage fluid were observed in the 8 mg/m³-exposed carcinogenicity groups. The aNTiO₂ deposited in the lungs of the satellite group rats was decreased at 26 weeks after the end of exposure compared to 1 day after the end of exposure. At 52 weeks after the end of exposure, the decreased level was the same at 26 weeks after the end of exposure.