Distribution and fate of antibiotics in water-sediment-biofilm phases and their potential risks in urban lakes within a large-scale city in eastern China.

Urban lakes often serve as the key nodes of material and energy flows in the river network ecosystems in large-scale cities. A comprehensive understanding of the multimedium distribution and fate of antibiotics in the lacustrine water-sediment-biofilm system is the critical prerequisite for their accurate ecological risk assessment and regional control and remediation. This study presents a comprehensive investigation of 21 antibiotics across six families in the water, sedimentary and biofilm phases of six typical urban lakes in Nanjing, a large-scale city in eastern China. The fates of these pollutants in multiple environmental compartments and their risks were assessed under real urban lake scenarios. The results indicated that the target antibiotics were ubiquitously present in the lakes. Quinolones (QNs) dominated all the lacustrine matrices, i.e., 10.63-38.78 ng/L in water, 0.4-12.77 ng/g in sediments, and not detected (ND) ∼73.30 ng/g in biofilms; wherein biofilms exhibit a much greater adsorption capacity to the chemicals than sediments, could serve as pollution markers owing to the significantly positive correlation between the concentration of QNs in the biofilm phase and the intensity of human activity (r = 0.92, p < 0.01). Notable differences in the cooccurrence patterns of antibiotics, metals and environmental factors among the biofilm, water and sedimentary phases were detected, of which the network in the biofilms was the most robust. An innovative model was developed to calculate the fugacity fractions of antibiotics in water, sediments and biofilms simultaneously, and the results suggested that biofilm accumulation would be the main fate of the target antibiotics in urban lakes. Risk assessment indicated that NOR posed a high ecological risk to algae in Xuanwu Lake, whereas most antibiotics posed low to no risk to aquatic organisms in urban lakes. Moreover, low antibiotic resistance development risks were obtained, except for ENR in Xuanwu Lake, which exhibited a moderate resistance risk. This study bridges a gap in knowledge of the distribution and environmental fate of antibiotics in the water, sediments and biofilms of urban lakes in large cities.