Antibiotic Pollution Characteristics and Ecological Risk Assessment in the Tidal Reach of the Minjiang River During Low-Water Periods Under Policy Intervention
The Minjiang River Basin, subjected to combined pollution from domestic, agricultural, and industrial sources, has become a typical sensitive area for studying the environmental behavior of emerging contaminants such as antibiotics. This study conducted a cross-year comparative analysis of the composition and concentrations of antibiotics in water samples from nine sampling sites during the dry season in November 2022 and 2024. The findings revealed: 1) After the implementation of the "National Action Plan for Reducing Antimicrobial Use in Livestock", the detection concentrations of tetracycline antibiotics (TCs) decreased (e.g., doxycycline concentrations dropped from 7.75 ng/L to undetectable levels), and the mixed risk quotient (MRQ) across the entire basin transitioned from medium to low risk. However, lincomycin (up to 4.6 ng/L), clarithromycin (1.3 ng/L), and florfenicol (0.6 ng/L) have emerged, indicating an increasing hidden ecological risk from substitution. 2) High-concentration antibiotic zones transferred from urban residential areas in 2022 to intensive aquaculture zones and upstream reservoir areas in 2024. The reduction in dry-season water flow intensified pollutant accumulation, synergistically enhancing the effects of tidal drag. Additionally, the conversion of agricultural land to aquaculture ponds led to increased use of alternative drugs (e.g., sulfamethazine), while policy interventions mitigated the exacerbation of urban antibiotic pollution by construction land. This study elucidates the migration patterns of antibiotic pollution under the synergistic effects of policy regulation and natural processes, emphasizing the need to address hidden risks of substitute drugs and the driving role of land-use changes, providing scientific basis for watershed-scale risk assessment and precise management of emerging pollutants.