Key Takeaways & Executive Findings
- •• • Policy intervention reduced tetracycline concentrations: doxycycline fell from 7.75 ng/L to undetectable, and basin-wide mixed risk quotient (MRQ) dropped from medium to low risk, demonstrating direct efficacy of source control. • • Hidden substitution risk emerged: lincomycin (up to 4.6 ng/L), clarithromycin (1.3 ng/L), and florfenicol (0.6 ng/L) were newly detected, indicating that policy-driven reduction of one antibiotic class can be offset by increased use of alternatives. • • Spatial shift of pollution hotspots: high-concentration zones moved from urban residential areas (2022) to intensive aquaculture zones and upstream reservoir areas (2024), driven by land-use conversion and tidal effects, with sulfamethazine reaching an extreme value of 1112.3 ng/L in aquaculture areas. • • Land-use and policy interaction: agricultural land positively correlated with sulfonamide and macrolide concentrations, while construction land dominated urban sources; effective policy intervention counteracted negative effects of construction land expansion, but aquaculture pond expansion amplified local pollution under tidal conditions.
Abstract
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.
1. Introduction
The Minjiang River Basin, a critical water system in southeastern China, faces compounded pollution pressures from domestic, agricultural, and industrial activities. Its tidal reach, particularly during low-water periods, becomes a sink for emerging contaminants such as antibiotics, which pose ecological risks even at trace concentrations. Previous management strategies focused on reducing antibiotic use in livestock, yet the dynamic response of antibiotic pollution to policy intervention and concurrent land-use changes remains poorly understood. This study addresses the gap by comparing antibiotic profiles in November 2022 and 2024, capturing the effects of the National Action Plan for Reducing Antimicrobial Use in Livestock.
Existing monitoring often targets legacy antibiotics, overlooking the potential for substitution with alternative drugs. Moreover, the interplay between hydrological conditions (e.g., tidal drag, reduced flow) and land-use transitions (e.g., agricultural land to aquaculture ponds) complicates pollution dynamics. By systematically analyzing nine sampling sites, this research quantifies shifts in antibiotic composition and ecological risk, revealing that while policy effectively curbed tetracycline pollution, it inadvertently fostered the emergence of substitute antibiotics. The findings underscore the necessity of adaptive monitoring and integrated watershed management to mitigate hidden risks.
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FU Junjie, MA Xiaodan, YE Zengjie, XIE Rongrong, CHEN Xi, YAN Zhenhua, ZHAO Xuan, LI Jiabing, HU Wei, JIANG Caiping, WANG Jiangfei, CHEN Wei, YUAN Yulan (2026). Antibiotic Pollution Characteristics and Ecological Risk Assessment in the Tidal Reach of the Minjiang River During Low-Water Periods Under Policy Intervention. Journal of Environmental Engineering Technology. https://doi.org/10.13205/j.hjgc.202608007
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Frequently Asked Questions
What evidence indicates that the observed reduction in tetracycline concentrations is directly attributable to the policy intervention rather than natural variability?
The study compared dry-season data from November 2022 and 2024, during which the National Action Plan for Reducing Antimicrobial Use in Livestock was implemented. Doxycycline concentrations dropped from 7.75 ng/L to undetectable levels, and the mixed risk quotient (MRQ) across the basin decreased from medium to low risk. These changes align temporally with the policy rollout, and the consistent decline across multiple tetracycline compounds suggests a causal link, though natural hydrological variations were not fully isolated.
How do tidal effects and reduced dry-season flow quantitatively influence antibiotic accumulation in the tidal reach?
The study observed that high-concentration zones shifted to aquaculture and reservoir areas in 2024, coinciding with reduced water flow and tidal drag. These conditions likely enhance pollutant accumulation by limiting dilution and promoting upstream transport. However, the paper does not provide quantitative flow or tidal measurements, so the exact contribution remains qualitative.
What are the implications of the extreme sulfamethazine concentration (1112.3 ng/L) for ecological risk in aquaculture zones?
This value, detected in aquaculture-intensive areas, far exceeds typical environmental levels and indicates a potential high-risk hotspot. It suggests that antibiotic use in aquaculture is a significant source, and the conversion of agricultural land to ponds may be driving increased use of sulfonamides. Such concentrations could exert selective pressure on microbial communities and pose risks to aquatic organisms, necessitating targeted management.
Which specific antibiotic classes are recommended for inclusion in routine monitoring based on the substitution risk identified?
The study recommends adding specific sulfonamides (e.g., sulfamethazine), macrolides (e.g., clarithromycin), and fluoroquinolones (e.g., florfenicol) to routine monitoring. These were newly detected or increased in concentration after policy intervention, indicating they are likely substitutes for banned or restricted antibiotics.
How can the proposed hydrological-pollution source joint model improve watershed management compared to current approaches?
The model would integrate hydrological dynamics (e.g., flow, tidal effects) with pollution source data to predict antibiotic transport and accumulation under varying conditions. This enables proactive management, such as optimizing monitoring locations and timing, and evaluating the impact of land-use changes on pollution, thereby supporting adaptive policy-making.
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