Antibiotics in urban wastewater and rivers of Tehran, Iran: Consumption, mass load, occurrence, and ecological risk

The continuous discharge of antibiotic pharmaceuticals from incomplete wastewater treatment processes into receiving water bodies has become a matter of both scientific and public concern as antibiotics may exert adverse influences on non-target organisms. In this study, the occurrence of seven most commonly prescribed antibiotics belonging to four therapeutic classes of β-lactams, cephalosporins, macrolides, and fluoroquinolones were investigated in the effluent of two wastewater treatment plants (WWTPs) and two river waters: Firozabad Ditch (receiving effluent) and Kan River (not receiving effluent) in Tehran, Iran. In 2016, average consumption rate of target antibiotics in Tehran province was evaluated based on Anatomical Therapeutic chemical (ATC)/Defined Daily Dose (DDD) system and reported as DDD/1000 inh/day. The highest consumption rate was for amoxicillin (128017.6 mg/1000 inhabitants/day), whereas it remained lower for other compounds (amoxicillin > cefixime > azithromycin > ciprofloxacin > cephalexin > erythromycin > penicillin). Ciprofloxacin (79.62 mg/1000 inh/d) and cephalexin (209.51 mg/inh/d) with highest mass loads were evaluated in the influent of WWTP A and WWTP B, respectively. Ciprofloxacin (24.87 mg/1000 inh/d) and cefixime (90.45 mg/1000 inh/d) were the highest evaluated mass loads in the effluent of Ekbatan wastewater treatment plant (WWTP A) and Tehran Southern wastewater treatment plant (WWTP B), respectively. The calculated risk quotients showed that six out of seven target antibiotics posed a high risk to algae (M. aeruginosa and P. subcapitata) and bacteria (P. putida) in the effluent of WWTPs and the rivers wherein amoxicillin and penicillin posed a higher risk than other antibiotics occurring due to their lowest PNEC.