• Oxytetracycline;
  • Antibiotics;
  • Related substances;
  • Production wastewater


This study investigated the occurrence and fate of oxytetracycline (OTC) and its related substances, 4-epi-oxytetracycline (EOTC), α-apo-oxytetracycline (α-apo-OTC), and β-apo-oxytetracycline (β-apo-OTC), in a wastewater treatment plant (WWTP) treating OTC production wastewater and a river receiving the effluent from the WWTP using liquid chromatography electrospray ionization mass spectrometry (LC-ESI-MS). The percent removal of OTC in the WWTP was 38.0 ± 10.5%, and the concentration of OTC was still up to 19.5 ± 2.9 mg/L in the treated outflow. The concentration slightly decreased along the river, from 641 ± 118 μg/L at site R2 (discharging point) to 377 ± 142 μg/L at site R4 (∼20 km from site R2), which was still higher than the minimal inhibition concentration of OTC reported (∼250 μg/L). On the other hand, the total amount of its related substances in the treated effluent was less than 5% of OTC. Concentrations of α-apo-OTC and β-apo-OTC increased along the river, from 5.76 ± 0.63 and 2.08 ± 0.30 μg/L at site R2 to 11.9 ± 4.9 and 12.0 ± 4.6 μg/L at R4, respectively, although EOTC decreased from 31.5 ± 3.8 to 12.9 ± 1.1 μg/L, respectively. The mean concentration of β-apo-OTC in river sediments was 20.8 ± 7.8 mg/kg, and its ratio to OTC was approximately 0.11, nearly twice the ratio of α-apo-OTC and EOTC to OTC (0.058 ± 0.014 and 0.061 ± 0.015, respectively).