Nano urea as a carrier for antibiotics: Enhanced bioavailability, phytotoxicity, and risk implications in Vigna radiata

Nano urea (NU) is a nano-enabled nitrogen fertilizer developed to improve nutrient use efficiency and crop productivity; however, its high surface reactivity raises the possibility of being a potential carrier for coexisting contaminants. Such behaviour of NU remains poorly understood in agricultural systems, particularly in soils contaminated with emerging pollutants such as tetracycline (TC), a widely used veterinary antibiotic. This study investigated the carrier effect of NU on TC and its influence on contaminant uptake and phytotoxicity in V. radiata, using bulk urea (BU) as a conventional control. Pristine TC exposure adversely affected plant physiological performance and metabolic responses, and these effects were further intensified under NU+TC co-exposure compared with BU+TC treatment. Fourier transform infrared spectroscopy analysis confirmed NU+TC interaction, and Liquid Chromatography-Mass Spectrometry (LC-MS) analysis revealed strong adsorption of TC toward NU, supporting its carrier potential. Furthermore, LC-MS analysis showed that NU+TC increased TC uptake by ∼22.7 mg/kg in roots and ∼5.7 mg/kg in shoots relative to pristine TC, confirming enhanced bioavailability in plants. This enhanced TC bioavailability induced oxidative stress, with NU+TC co-exposure amplifying ROS generation by ∼18% relative to pristine TC, leading to impaired metabolic responses and reduced nutrient uptake, whereas BU+TC caused no significant effect. Overall, the findings demonstrated that NU acts as a carrier for TC, promoting its accumulation in plants and intensifying antibiotic-induced phytotoxicity. These results highlight an environmental and human risk associated with nano fertilizer application and the need to evaluate interactions with coexisting contaminants in agricultural systems.