Occurrence, spatial distribution, and ecological and human health risks of antibiotic residues in the River Jhelum.

Antibiotic residues in riverine environments are emerging contaminants of concern because of their persistence, ecological effects, and potential contribution to antimicrobial resistance. This study investigated the occurrence, spatial distribution, pollution status, and screening-level ecological and human-health risks of six antibiotics in the River Jhelum, Pakistan. Surface-water samples were collected from ten monitoring sites representing upstream, midstream, and downstream reaches during a post-monsoon sampling campaign. Antibiotics were quantified using High Performance Liquid Chromatography coupled with photodiode-array detection, while single-factor and comprehensive pollution indices and GIS-based spatial interpolation were applied to characterize contamination patterns. Azithromycin exhibited the highest concentration (20.30 µg/L), followed by ofloxacin (12.70 µg/L), ciprofloxacin (8.03 µg/L), linezolid (4.55 µg/L), cefixime (1.40 µg/L), and levofloxacin (0.51 µg/L). Azithromycin showed the greatest pollution burden across the monitoring sites investigated, whereas levofloxacin exhibited comparatively limited contamination. The comprehensive pollution assessment indicated substantial combined antibiotic contamination across the investigated river transect. Azithromycin produced the highest ecological risk quotient (RQ = 17.41), indicating high predicted ecological risk under the applied screening framework. Human health hazard quotients remained below unity, indicating non carcinogenic risks. These findings strengthen wastewater management, pharmaceutical discharge controls, and systematic monitoring of antibiotic residues in the River Jhelum.