Usage of titanium dioxide nanoparticles (TiO2 NPs) and tetracycline (TC) has increased significantly in the present era.This leads to their release and accumulation in the environment.Both the compounds,individually,can have adverse toxic effects on the plants.Their binary mixtures can increase this degree of damage.The present study aimed to evaluate the toxicity of both the contaminants in individual and binary mixtures in Allium cepa.Further,the toxicity ofTiO2 NPs upon UVA pre-irradiation was also measured.Results showed that UVA pre-irradiated NPs (UVA-TiO2 NPs) had a significant decrease in cell viability than their non-irradiated counterparts (NI-TiO2),denoting an increase in photocatalytic activity upon UVA pre-irradiation.Very low concentrations of TC (EC1o =0.016 μmol/L) mixed with TiO2 NPs significantly increased the toxicity for both UVA-TiO2 and NI-TiO2 NPs.Intracellular ROS generation was significantly high for UVA-TiO2 NPs.However,TC did not have any effects on ROS production.Both the compounds exhibited genotoxic potential in A.cepa.Different chromosomal abnormalities like anaphase bridges,telophase bridges,laggard chromosomes,binucleate cells,etc.were observed.The binary mixture ofUVA-TiO2 NPs and TC showed the highest chromosomal aberrations (64.0％t1.26％) than the mixture with NI-TiO2 or the individual contaminants.This decreased significantly after recovery (46.8％41.92％),denoting the self-repair processes.This study proved that UVA-TiO2 NPs were more toxic and could be enhanced further when mixed with a sub-lethal concentration of TC.This work will help to assess the risk of both compounds in the environment.