Antibiotic residues in Sabarmati River, Gujarat (India): Insight into occurrence, seasonal dynamics and risk to aquatic ecosystems

The study conducted in the Sabarmati River spanned seven months, covering the pre-monsoon, monsoon, and post-monsoon seasons, and focused on five selected antibiotics. Studied antibiotics include Ciprofloxacin (CIP), Sulfamethoxazole (SMX), Meropenem (MPN), Trimethoprim (TPM), and Ampicillin (AMP) by using a modified LC-MS/MS method with QuEChERS (Quick, Easy, Cheap, Effective, Rugged, and Safe) extraction. All the studied antibiotics were detected at least once in the river with maximum concentrations of 0.0012 µg/L (TPM) to 9 µg/L (CIP). High concentrations were detected during the monsoon and post-monsoon seasons, while the pre-monsoon season recorded low concentrations to most antibiotics. Ciprofloxacin was the highest and most frequently detected antibiotic, followed by sulfamethoxazole, while meropenem, ampicillin, and trimethoprim were detected at deficient concentrations. In contrast, the inter-site mean difference in antibiotic concentrations was not significant despite several sewage treatment points and hospitals on the riverside. The observations above suggested temporal variations of the antibiotic concentrations in the river across seasons but no significant spatial variations along the river. The analysis revealed that the temporal variation was significant at (***p < 0.05) than the spatial variation demonstrated by the observed trend. This fluctuation in antibiotic concentration was primarily driven by seasonal and monthly changes rather than the difference in concentration between sampling sites. The risk quotient for ciprofloxacin was high for algae, daphnia, and fish, especially in September, October, and November whereas sulfamethoxazole displayed a high risk in algae only. Other studied antibiotics including ampicillin, meropenem, and trimethoprim, demonstrated no perceptible risk to any of the studied organisms.