Long‐term observation of pulmonary toxicity of toner with external additives following a single intratracheal instillation in rats

Objectives Along with technological innovations for improving the efficiency of printing, nanoparticles have been added to the surface of toners, and there is concern about the harmful effects of those components. We investigated, through a long‐term observation following intratracheal instillation using rats, whether exposure to a toner with external additives can cause tumorigenesis. Methods Female Wistar rats were intratracheally instilled with dispersed toner at low (1 mg/rat) and high (2 mg/rat) doses, and the rats were sacrificed at 24 months after exposure, after which we examined pulmonary inflammation, histopathological changes, and DNA damage in the lung. Rats that had deceased before 24 months were dissected at that time as well, to compare tumor development. Results Although alveolar macrophages with pigment deposition in the alveoli were observed in the 1 and 2 mg exposure groups, no significant lung inflammation/fibrosis or tumor was observed. Since immunostaining with 8‐OHdG or γ‐H2AX did not show a remarkable positive reaction, it is thought that toner did not cause severe DNA damage to lung tissue. Conclusion These results suggest that toner with external additives may have low toxicity in the lung.