The occurrence and fate of tetracyclines in two pharmaceutical wastewater treatment plants of Northern China

Several parameters of the method, solid-phase extraction (SPE)-ultra-performance liquid chromatography (UPLC)-tandem mass spectrometry (MS/MS), were optimized to investigate the presence and partitioning of 18 antibiotics (including sulfonamides, tetracyclines, quinolones, macrolides, and beta-lactams) during various processing stages at two typical pharmaceutical wastewater treatment plants (PWWTPs) in northern China. Oxytetracycline (OTC), chlortetracycline (CTC), and tetracycline (TC) were all detected in each stage of both PWWTPs. Antibiotics were largely removed through biological units of both PWWTPs, with removal efficiencies of 62.0 to 78.3 %. Mass balance analyses indicated that degradation (44.8-53.7 % for PWWTP1 and 40.1-59.6 % for PWWTP2) was the major mechanism responsible for the removal of tetracyclines, whereas the contribution of sorption by sludge (12.6-20.0 % for PWWTP1 and 18.7-33.5 % for PWWTP2) was less significant for the investigated pharmaceuticals. Although there was significant removal of tetracyclines through PWWTPs, large amounts of tetracyclines were still discharged through the effluent (up to 32.0 +/- 6.0 mg L-1) and dewatered sludge (up to 5,481.1 +/- 123.0 mg kg(-1)), which increased the risk of selecting for antibiotic resistance in the receiving water and soil environments.