Mechanism and synergistic effect of sulfadiazine (SDZ) and cadmium toxicity in spinach (Spinacia oleracea L.) and its alleviation through zinc fortification

Cadmium (Cd) and antibiotic’s tendency to accumulate in edible plant parts and fertile land is a worldwide issue. The combined effect of antibiotics and heavy metals on crops was analyzed, but not mitigation of their toxicity. This study investigated the potential of zinc oxide nanoparticles (ZnO NPs) to alleviate the SDZ and Cd toxicity (alone/combined) to promote spinach growth. Results revealed that the ZnO 200 mg L^-1 spray decreased the malondialdehyde (MDA) 14%, hydrogen peroxide (H₂O₂) 13%, and electrolyte leakage (EL) 7%, and increased the superoxide dismutase (SOD) 8%, peroxidase (POD) 25%, catalase (CAT) 39% and ascorbate peroxidase (APX) 12% in spinach leaves under combined SDZ+Cd (25 mg Kg^-1+50 mg Kg^-1) stress compared to ZnO 100 mg L^-1 spray. Likewise, ZnO NPs 200 mg L^-1 spray enhanced the zinc (Zn) 97%, iron (Fe) 86%, magnesium (Mg) 35%, manganese (Mn) 8%, and potassium (K) 23% in shoots under combined SDZ+Cd (25 mg Kg^-1+50 mg Kg^-1) stress compared to ZnO 100 mg L^-1 spray. Further, ZnO 200 mg L^-1 spray reduced Cd uptake in roots by 9% and shoots 15% under combined SDZ+Cd (25 mg Kg^-1+50 mg Kg^-1) stress compared to ZnO 100 mg L^-1. Overall, ZnO NPs alleviated the SDZ and Cd toxicity and enhanced spinach growth in all treatments.