Trace determination of sulfonamide antibiotics and their acetylated metabolites via SPE-LC-MS/MS in wastewater and insights from their occurrence in a municipal wastewater treatment plant.

Antibiotics have drawn much attention as their wide usage in humans and animals may result in microbial resistance, which is a huge threat to humans' health. Studies on the occurrence and removals of antibiotics in wastewater treatment plants have been widely performed, but very few covered their main acetylated metabolites. This study developed an effective analytical method for the trace determination of four sulfonamides and three acetylated metabolites in municipal wastewaters, which was validated by linearity (R2  > 0.995), sensitivity (limit of quantification, LOQ < 0.78 ng/L), recovery (77.7%-148.1%) and precision (relative standard deviation, RSD < 9.6%). All sulfonamides and their acetylated metabolites were detected in municipal wastewaters including influent, primary settling tank and effluent. Removal performances of sulfapyridine (SP), sulfadiazine (SDZ), sulfamethoxazole (SMZ), and N4 -acetyl sulfadiazine (AC-SDZ) in the municipal wastewater treatment plant were moderate or excellent, whereas the corresponding removals of sulfamethazine (SM2), N4 -acetyl sulfapyridine (AC-SP), and N4 -acetyl sulfamethazine (AC-SM2) were poor. The calculated poor removal of SM2 might be attributed to its fluctuation in raw wastewater, whereas the poor removals of AC-SP and AC-SM2 may be due to re-transformation from their parent sulfonamides. Our results showed that monitoring of acetylated sulfonamides in municipal wastewater is important for two reasons. One is that acetylated metabolites are good biomarkers for wastewater-based epidemiology when they are combined with their corresponding parent sulfonamides. The other is that the potential risk of sulfonamides in effluent to the natural environment cannot be accurately evaluated unless their acetylated metabolites are also accounted. This report is the first to address the potential risk of acetylated sulfonamides in effluent of wastewater treatment plants.