Sediment-water interface reoxygenation by NO₃-LDH promotes tetracycline degradation in sediments and modulates antibiotic resistance gene dynamics

The widespread presence of antibiotics in aquatic sediments, together with hypoxic conditions, constrains oxygen-driven natural degradation, thereby prolonging their environmental persistence. In this work, nitrate-intercalated layered double hydroxide (NO₃-LDH) was employed as a controlled-release nitrate amendment to alleviate interfacial oxygen limitation while minimizing the secondary environmental risks associated with the high release peaks of conventional nitrate reagents. As a result, NO₃-LDH increased dissolved oxygen (DO) from 1.05 to 3.39 mg/L, enhanced TC removal from 64.5% to 89.8% within 15 d, and reduced the combined abundance of tetracycline resistance genes (tetA, tetQ, and tetS) by 53.0%. Mechanistically, DO enrichment increased •OH generation 1.94-fold and upregulated cytochrome P450-related genes, supporting coupled enhancement of abiotic oxidation and oxygen-dependent microbial transformation. The improved oxidative microenvironment also favored the enrichment of aerobic aromatic-degrading taxa, further promoting TC attenuation. Although overall antibiotic resistance genes (ARGs) levels declined, fluoroquinolone- and macrolide-associated ARGs exhibited a transient early increase, likely triggered by an abrupt redox perturbation upon oxygen recovery that imposed oxidative stress on anaerobic microorganisms, intensified ATP-demanding stress responses, and increased membrane permeability. As interfacial redox conditions stabilized and TC concentrations decreased, these stress responses subsided and ARGs abundances declined at later stages. Overall, restoring interfacial DO strengthens oxygen-driven natural antibiotic degradation and inhibits the long-term accumulation of ARGs, providing a mechanistically grounded strategy for in situ remediation of antibiotic-contaminated sediments.