Occurrence, removal, and risk assessment of antibiotics in 12 wastewater treatment plants from Dalian, China

In this study, the occurrence and removal efficiencies of 31 antibiotics, including 11 sulfonamides (SAs), five fluoroquinolones (FQs), four macrolides (MLs), four tetracyclines (TCs), three chloramphenicols (CAPs), and four other antibiotics (Others), were investigated in 12 municipal wastewater treatment plants (WWTPs) in Dalian, China. A total of 29 antibiotics were detected in wastewater samples with the concentration ranging from 63.6 to 5404.6 ng/L. FQs and SAs were the most abundant antibiotic classes in most wastewater samples, accounting for 42.2 and 23.9% of total antibiotic concentrations, respectively, followed by TCs (16.0%) and MLs (14.8%). Sulfamethoxazole, erythromycin, clarithromycin, azithromycin, ofloxacin, and norfloxacin were the most frequently detected antibiotics; of these, the concentration of ofloxacin was the highest in most of influent (average concentration = 609.8 ng/L) and effluent (average concentration = 253.4 ng/L) samples. The removal efficiencies varied among WWTPs in the range of -189.9% (clarithromycin) to 100% (enoxacin, doxycycline, etc), and more than 50% of antibiotics could not be efficiently removed with the removal efficiency less than 65%. An environmental risk assessment was also performed in the WWTP effluents by calculating the risk quotient (RQ), and high RQ values (> 1) indicated erythromycin and clarithromycin might cause the ecological risk on organisms in surrounding water near discharge point of WWTPs in this area, which warrants further attention.