Synergistic Effects of Oxytetracycline on Pendimethalin Persistence and Ecological Risks in a Soybean–Soil System

The frequent detection of oxytetracycline in agricultural soils may alter the environmental behavior and risks of coexisting pesticides. This study investigated the influence of oxytetracycline on the degradation and phytotoxicity of pendimethalin in a soil–soybean system. Results demonstrated that oxytetracycline at 50 mg/kg prolonged the half-life of pendimethalin in soil from 33.0 days to 40.8 days. Coexposure inhibited the activities of urease, dehydrogenase, and catalase in the soil. While pendimethalin alone showed no adverse effects on soybean growth, coexposure with oxytetracycline induced pronounced growth inhibition and enhanced oxidative stress. Ecological risk assessment confirmed significantly elevated risks to earthworms. Further analysis revealed suppressed CYP450 and GST activities in both soil and soybean plants, with more pronounced reductions observed in the plants. These findings indicate that the coexistence of antibiotic–herbicide can enhance herbicide persistence and increase environmental contamination risks.