Mechanism of adsorption and biodegradation of typical antibiotics by sediments in mariculture tailwater system

Antibiotics are extensively used in mariculture, leading to their persistent accumulation in sediments and posing ecological and health risks. Sediments act as both major sinks and active sites for antibiotic transformation, yet the mechanisms remain poorly understood. This study examined the roles of sediment adsorption and biodegradation in removal of enrofloxacin (ENR), oxytetracycline (OTC), and sulfamethoxazole (SMZ) commonly used in mariculture. ENR and OTC were primarily removed via adsorption (88 % and 86 %), whereas SMZ removal involved both adsorption and biodegradation (54 % and 56 %). Sediments exhibited the highest adsorption capacity for ENR (0.971 mg/g) versus OTC (0.495 mg/g) and SMZ (0.221 mg/g), with adsorption dominated by chemisorption and fitting pseudo-second-order kinetics and the Langmuir model. Bacterial communities showed higher diversity and richness than archaeal communities, with bacterial structures varying more among different treatment units. Dominant taxa included Sulfurovum (bacteria) and Methanosarcina (archaea), and rare taxa displayed pronounced spatial specificity. Biodegradation was driven by drug metabolism genes (e.g., IMPDH/guaB, GST/gst) and antibiotic resistance genes (e.g., β-lactam: penA, cfxA; multidrug: cmeA, marC), with key enzymes (transferases, oxidoreductases, and hydrolases) facilitating structural modification and bond cleavage. Potential antibiotic-degrading microorganisms (Lachnoclostridium, Microbulbifer, Carboxylicivirga and Candidatus_Nitrosopumilus) contributed to multi-antibiotic removal. Structural equation modeling (SEM) showed that adsorption enabled initial capture, while biodegradation was the key determinant (path coefficient = 2.198, p < 0.01). This study provides sediment-mediated antibiotic removal and provide guidance for optimizing mariculture tailwater treatment.