Spatiotemporal dynamics and ecological risks of antibiotics and antibiotic resistance genes in a typical tropical river-bay system: Insights from Sanya, China

Antibiotics and antibiotic resistance genes (ARGs) represent a critical threat to global public and environmental health. While their occurrence is widely reported, the spatiotemporal dynamics and propagation mechanisms within tropical river-bay systems, remain inadequately understood. This study presents a comprehensive investigation of 46 antibiotics and 51 ARGs in the river-bay system of Sanya, a representative tropical tourist city in China, across distinct wet and dry seasons. The predominant antibiotics were identified as quinolones and tetracyclines, with concentrations ranging from not detected (ND) to 50.98 ng/L and from ND to 122.22 ng/L, respectively. Absolute ARGs abundances ranged from ND to 4.72 × 10 7 copies/L, with aminoglycoside, MLSB, and tetracycline resistance genes being the most abundant ARGs. Their distribution exhibited significant spatiotemporal heterogeneity, primarily driven by seasonal wastewater discharges from tourism, agricultural and livestock runoff, and varying hydrological conditions. Ecological risk assessment indicated that antibiotic mixtures persistently posed a high risk to algae, with ciprofloxacin and chlortetracycline classified as priority pollutants. Co-occurrence network analysis further revealed more intricate and robust ARG-bacteria interactions during the dry season, suggesting that seasonal forces such as low flow and intensified human activities, promote the selection of multidrug-resistant bacteria. Our findings demonstrate that tropical coastal ecosystems are vulnerable to antibiotic and ARG pollution, which is governed by the interplay of anthropogenic influences and natural hydroclimatic factors, necessitating tailored monitoring and mitigation strategies. • Widespread antibiotics and ARGs were found in Sanya's river-bay system. • Antibiotic pollution was moderate-low, dominated by quinolones and tetracyclines. • Tourism, agriculture, and hydrology influenced antibiotic and ARG distribution. • Ciprofloxacin and chlortetracycline were identified as priority pollutants. • Dry-season conditions promoted ARG-bacteria co-occurrence and multidrug resistance.