Occurrence and fate of most prescribed antibiotics in different water environments of Tehran, Iran.

The presence of most prescribed antibiotic compounds from four therapeutic classes (β-lactam, cephalosporins, macrolides, fluoroquinolones) were studied at two full-scale WWTPs, two rivers, thirteen groundwater resources, and five water treatment plants in Tehran. Analytical methodology was based on high performance liquid chromatography/tandem mass spectrometry after solid-phase extraction. Samples were collected at 33 sample locations on three sampling periods over four months from June to August 2016. None of the target antibiotics were detected in groundwater resources and water treatment plants, while seven out of nine target antibiotics were analyzed in two studied river waters as well as the influent and effluent of wastewater treatment plants at concentrations ranging from <LOQ to 926.32ng/L. Ciprofloxacin predominated in all analyzed influent (552.6-796.2ng/L) and effluent (127-248.7ng/L) samples of WWTP A, whereas cephalosporins including cephalexin (523.3-977.7ng/L) and cefixime (278.65 to 422.1ng/L) were the most abundant detected antibiotics in the influent and effluent of WWTP B. Aqueous phase removal efficiencies were assessed and ranged from 339.83% to 100% for the seven detected antibiotics. "Negative removals" were observed for erythromycin, azithromycin, and cefixime due to the deconjugation of conjugated metabolites via biological transformation in the studied WWTPs. From a statistical point of view, significant differences (p<0.05) were observed in the concentrations of cefixime, cephalexin, azithromycin, and erythromycin in the effluent of both studied WWTPs. Ciprofloxacin and cephalexin were the most abundant detected antibiotics in the two studied river waters. Statistical results revealed that there were significant differences in the concentrations of ciprofloxacin, azithromycin, and erythromycin (p<0.05) in Firozabad ditch (receiving WWTP effluent) and Kan River (non-receiving WWTP effluent) which demonstrated that WWTPs discharges could be an important source of antibiotics being released in water bodies.