P29-12 Four-Week Repeated Inhalation Toxicity Study of SiO2-ZnO Mixed Nanoparticles in Sprague-Dawley Rats

The widespread industrial application of nanomaterials has increased the potential for exposure to various combinations of nanomaterials. Mixed nanoparticles, in particular, may exhibit toxicological properties different from their single components, yet systematic toxicity studies on mixed nanoparticles remain limited. This study investigated the toxicity of SiO2-ZnO mixed nanoparticles following repeated inhalation exposure in male Sprague-Dawley rats (6 weeks old) divided into control and three exposure groups (G1, G2, G3). All exposure groups received the same concentration of SiO2-ZnO mixed nanoparticles (416.17 mg/m 3 of mean acutal concentration) but with different exposure durations (G1: 30 min/day, G2: 90 min/day, G3: 360 min/day) to evaluate dose-response relationships. Following 4 weeks of nose-only inhalation exposure (5 days/week, 20 exposures total), assessments included body weight, food consumption, hematology, clinical chemistry, macroscopic observation, organ weight measurement, histopathological examination, and bronchoalveolar lavage fluid (BALF) analysis. The geometric mean diameter of the exposed particles was 34.84±3.17nm with a geometric standard deviation (GSD) of 1.85±0.06. No mortality was observed during the exposure period. The G3 exposure group exhibited significant decreases in body weight and food consumption. Macroscopic changes (pale discoloration) in the lungs and significant increases in absolute and relative lung weights were observed in G2 and G3 exposure groups. Histopathological examinations revealed test item-related changes in the respiratory tract (nasal cavity, lungs, trachea, and larynx). In the nasal cavity, degeneration/ necrosis and atrophy of olfactory epithelium were observed in all exposure groups, with mucous cell hyperplasia and cellular debris in G2 and G3, and inflammatory cell infiltration in G3. In the lungs, inflammatory cell infiltration in perivascular/alveolar regions and alveolar histiocytosis/proteinosis were observed in all exposure groups, while alveolar epithelial hyperplasia/thickened alveolar wall was noted in G2 and G3, and mineralized debris in G3. BALF analysis showed significant increases in total cell count, neutrophil values, LDH, and total protein levels, along with significant decreases in macrophage values in G2 and G3 exposure groups. This study demonstrates that 4-week repeated inhalation exposure to SiO2-ZnO mixed nanoparticles induces significant toxic effects in the nasal cavity and lungs of rats, suggesting potential health risks from occupational and environmental exposure to such mixed nanoparticles. These findings highlight potential health risks from occupational and environmental exposure to mixed nano-particles and emphasize the need for systematic toxicological evaluation of various nanoparticle combinations with different compositions and ratios.