Occurrence, distribution, and risk assessment of antibiotics in post-harvest and drained ponds of Sheyang River estuary in Jiangsu Province: Implications for sustainable aquaculture management.

Antibiotic contamination in aquaculture has long been a critical problem, jeopardizing aquatic ecosystems, food security, and human health. However, the post-harvest antibiotic residues in drained ponds, critical for guiding subsequent farming cycles, remain poorly understood. This study systematically investigated 20 target antibiotics in white shrimp aquaculture ponds at the Sheyang Estuary, Jiangsu Province, China, focusing on sediments and the low-lying area residual water sampled three months after harvest and drainage. Sixteen antibiotics were detected in residual water at total concentrations ranging from 19.3 ng/L to 28.4 ng/L and ten antibiotics were detected in sediments at total concentrations ranging from 9.49 ng/g to 65.9 ng/g. Tetracyclines (TCs) were the dominant antibiotic class, with chlortetracycline (CTC) prevalent in water and doxycycline (DXC) dominant in sediments. Notably, prohibited antibiotics were detected, with ofloxacin (OFX) posing medium ecological risk. Furthermore, 80 % of ponds showed medium ecological risk from antibiotic mixtures. Ciprofloxacin (CLX) was identified as the sole priority antibiotic posing both ecological and resistance risks. Rewatering ponds for subsequent cycles may trigger sediment-water exchange, remobilizing sediment-bound antibiotics into the water column. In this study, pre-cycle sediment screening is proposed to quantify residual antibiotic levels. Adaptive dosing strategies should prioritize reducing inputs of antibiotics exhibiting significant residual concentrations from previous cycles. This research, focusing on post-drainage residues in a typical estuarine aquaculture area, provides novel scientific guidance for sustainable antibiotic use and supports the long-term health of aquaculture systems.