Copper-induced the genotoxicity enhancement of cadmium and oxytetracycline combined pollutants in rice

The coexistence of heavy metals and antibiotics in agricultural soil poses a critical challenge to crop safety. However, the molecular mechanisms underlying their combined toxic effects in real multi-pollutant environments remain poorly understood. This study elucidated the genotoxic mechanisms underlying the effects of cadmium (Cd) and oxytetracycline (OTC) on rice ( Oryza sativa L.) in the presence of copper (Cu). Results indicated that ambient Cu (50 mg/kg) significantly reduced Cd and OTC accumulation in rice roots by 86.6 % and 68.9 %, respectively. Density functional theory calculations further confirmed that this reduction stemmed from the formation of stable OTC-Cd-Cu ternary complexes. Despite the reduced uptake of Cd and OTC, Cu unexpectedly enhanced genotoxicity. Specifically, compared to the OTC-Cd group, the OTC-Cd-Cu group induced more DNA strand breaks. Further mechanistic investigations showed that Cu induced downregulation of the cell cycle regulators CYCB1 (by 20 %) and WEE1 (by 17.9 %), resulting in inhibition of G2/M transition and impaired DNA repair. Molecular dynamics simulations revealed that Cu enhanced the binding energy between DNA and OTC-Cd (-4178.17 kJ/mol), thereby destabilizing the DNA structure, as evidenced by circular dichroism analysis. Furthermore, thermodynamic parameter analysis suggested that the interaction between DNA and pollutants was an exothermic reaction. Importantly, the OTC-Cd-Cu ternary system exhibited a higher degree of impairment to DNA stability than the OTC-Cd binary system. These findings provide critical insights into the molecular basis of crop toxicity in agricultural soil and underline the urgency of comprehensive risk assessment of combined pollutants.