Determination and fate of oxytetracycline and related compounds in oxytetracycline production wastewater and the receiving river

This study investigated the occurrence and fate of oxytetracycline (OTC) and its related substances, 4-epi-oxytetracycline (EOTC), alpha-apo-oxytetracycline (alpha-apo-OTC), and beta-apo-oxytetracycline (beta-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 mu g/L at site R2 (discharging point) to 377 +/- 142 mu g/L at site R4 (similar to 20 km from site R2), which was still higher than the minimal inhibition concentration of OTC reported (similar to 250 mu g/L). On the other hand, the total amount of its related substances in the treated effluent was less than 5% of OTC. Concentrations of alpha-apo-OTC and beta-apo-OTC increased along the river, from 5.76 +/- 0.63 and 2.08 +/- 0.30 mu g/L at site R2 to 11.9 +/- 4.9 and 12.0 +/- 4.6 mu g/L at R4, respectively, although EOTC decreased from 31.5 +/- 3.8 to 12.9 +/- 1.1 mu g/L, respectively. The mean concentration of beta-apo-CTC in river sediments was 20.8 +/- 7.8 mg/kg, and its ratio to OTC was approximately 0.11, nearly twice the ratio of alpha-apo-OTC and EOTC to OTC (0.058 +/- 0.014 and 0.061 +/- 0.015, respectively).