Multimedia migration and ecological risks of bisphenol A in semiarid urban rivers: a case study of Xi'an, China.

Urban rivers in semiarid regions face intensified bisphenol A (BPA) contamination due to limited dilution capacity, extended low-flow periods, and pronounced seasonal hydrological variability. This study investigated BPA distribution and migration dynamics across water-sediment-fish compartments in Xi'an's river network (northwestern China) through spatial-temporal monitoring and multimedia coupling (MMC) modeling. BPA concentrations ranged 0.08-3.65 μg/L (water), 5.32-68.45 μg/kg (sediment), and 12.5-156.8 μg/kg (fish tissue), with wet season concentrations 115-166% higher than dry season values. Sediments exhibited 23-50-fold enrichment relative to overlying water, functioning as accumulation sinks during extended dry periods (October-May) and transforming into secondary pollution sources during wet seasons (June-September) through storm-driven resuspension, with annual water-sediment exchange flux estimated at 2.35 tons. MMC modeling revealed sediment-biota routes contributed 52-67% of total BPA accumulation in benthic omnivorous fish, challenging conventional aqueous-exposure assessment frameworks. Risk assessment identified elevated ecological risks in 12% of watershed area, with 36% of monitoring stations exceeding aquatic toxicity thresholds (PNEC: 1.5 μg/L). Principal component analysis demonstrated anthropogenic activity intensity (48.5% explained variance) and natural attenuation capacity (28.3% variance) as orthogonal regulatory axes. These findings highlight sediment-dominated migration, benthic food chain importance, and seasonal flux reversals as distinctive features of semiarid systems, informing integrated management for comparable water-limited urban watersheds globally.