Background and aims: Titanium dioxide (TiO₂) nanoparticles are used widely in the world. The present study was conducted to evaluate the lasting of pulmonary toxicity induced by nano-TiO₂ particles.

Methods: In this experimental study, 60 male rats were randomly divided in three groups. Furthermore, rats in each group were subdivided in four subgroups of 5 in each. Rats in subgroups 1, 2 and 3 of each group were intratracheally instilled with 25, 50, or 100mg/kg of TiO₂ particles, respectively. Rats in subgroup 4 (control group) of each group received the same volume of normal saline, intratracheally. On days 15, 30 and 45 after injection, rats in groups 1, 2 and 3 were anaesthetized, respectively. Radiographic pictures were taken and rats were then sacrificed. Blood and tissue samples were collected, subsequently. Results from hematologic and biochemical studies were analyzed statistically using ANOVA and Tukey test, results of the radiographic and pathological studies were analyzed statistically using Fisher exact test.

Results: The results showed significant difference of total WBC, Lymphocytes, monocytes, Granulocytes percentages and serum activity of LDH and ALP on day 15 of experiment. Moreover, histopathologic and radiographic examination of lung tissues indicated that
the pulmonary response to exposure to TiO₂ particles in rats manifested as dose-dependent inflammatory lesions, which mainly consisted of infiltration of inflammatory cells and interstitial thickening.

Conclusion: These results suggest that consumed dose may have important role in pulmonary toxicity and inflammatory effects of TiO₂ nanoparticles sustained for a limited time and rat recovered from these effects after a length of time.