Genotoxicity study of nano Al₂O₃, TiO₂ and ZnO along with UV-B exposure: An Allium cepa root tip assay

The present effort aims to investigate the cytotoxic and genotoxic impact of three widely used nanoparticles (ZnO, TiO₂ and Al₂O₃) on root cells of Allium cepa as a test organism. The root tip of Allium cepa were treated with three different concentrations (0.1 10 and 100 mg/L) of the above-mentioned NPs and the observations were recorded after proper growth of root under both nanoparticle solutions and UV-B exposure in combined conditions and separately. The parameters such as mitotic index, various forms of chromosomal aberrations, various reactive oxygen species (ROS) generation such as superoxide radical (O^-_2·), hydrogen peroxide, hydroxyl radical (·OH), lipid peroxidation and bio-uptake of nanoparticles were assessed. The results revealed that for all the three nanoparticles, mitotic index (MI) was highly reduced in comparison to control. Among the three nanoparticles, the MI value of TiO₂ was 59.5% at 0.1 mg/L. Chromosomal aberration data suggest that nano Al₂O₃ exhibited disturbed metaphase at 0.1 mg/L, and abnormal anaphase and sticky metaphase at 10 and 100 mg/L, respectively. Similarly, lagged metaphase and anaphase with multiple chromatin bridges were recorded for both nano ZnO and nano TiO₂ at 0.1 mg/L. But, nonsignificant (p > 0.05) results were recorded between only nano metal oxide and UV-B along with nano metal oxide. ROS generation data revealed that ZnO is more active under UV-B than TiO₂ and Al₂O_3. The cellular deformation and the existence of metal in A. cepa under nano ZnO, TiO₂ and Al₂O₃ treatment were evaluated by Scanning Electron Micrograph (SEM) and X-ray fluorescence (XRF) study, respectively. It may safely be concluded that with respect to chromosomal aberration and mitotic index, out of the three nanoparticles, Al₂O₃ is the most severe at higher concentrations and nano ZnO shows lowest mitotic index under UV-B exposure.