Antibiotic residues in reservoir-adjacent soils: Drivers, sources, and ecological risks.

Reservoirs are vital drinking-water sources, yet research has largely overlooked antibiotic accumulation in surrounding soils, which can act as terrestrial sinks and secondary sources that reintroduce contaminants into surface waters, pose latent ecological and public-health risks. This study investigated the occurrence, spatial heterogeneity, and ecological risks of soil antibiotics across three land-use types (cropland, forest land, and construction land) surrounding the Jinze Reservoir, Shanghai. A mixed-effects model and a Positive Matrix Factorization (PMF) model were applied to identify key environmental drivers and dominant pollution sources. The results indicated that fluoroquinolones and tetracyclines were the predominant contaminants, with detection frequencies of 97.0% and 77.8% and mean concentrations of 14.17 μg/kg and 4.84 μg/kg, respectively. Antibiotic composition and distribution differed significantly across land-use types (p < 0.05), with cropland exhibiting the highest contamination levels. Spatial distribution analysis indicated that surface runoff and irrigation return flows promote antibiotic transfer between adjacent land parcels. Mixed-effects modeling revealed that soil pH and organic carbon are key factors shaping antibiotic distribution (p < 0.05). PMF analysis identified agricultural manure application (44 %) and aquaculture effluents (56%) as the main contributors to soil antibiotic residues. Risk assessment indicated that most antibiotics posed low to medium ecological risks (RQ < 1). These findings highlight the need for class-specific monitoring and management for reservoir-adjacent soils, prioritizing soil physicochemical properties for fluoroquinolones (FQs), heavy metals for tetracyclines (TCs), and nutrients for sulfonamides (SAs), particularly in hotspot and near-shore areas, to strengthen drinking-water source protection, with clear implications for environmental management.