Determination of imipenem and vancomycin in the hospital wastewater, influent and effluent of Tabriz wastewater treatment plant

Abstract

Introduction: Antibiotics are among pollutants that can enter into hospital and municipal sewage due to the extremely wide use in hospitals to treat infectious diseases. Elevated use of antibiotics increases antibiotic-resistant bacteria species in the environment. Vancomycin and imipenem are two important antibiotics, which commonly used to treat sever bacterial infections. Unfortunately, in recent years, indiscriminate and unreasonable use of these antibiotics will cause their appearance in the aquatic environments. The purpose of this study was to determine vancomycin and imipenem in hospital wastewater and in the inlet and outlet of municipal wastewater treatment plant. Materials and Method: Composite samples were collected in the morning and evening from the nearest sanitary sewer manhole of the hospital. Also grab samples were obtained from the inlet and outlet of wastewater treatment plant. Samples were stored in dark and temperature of 4°C and carried to the laboratory. Samples were centrifuged and passed through 0.45 µm filter. Samples were extracted up to 24 hours after sampling and stored at -18 °C until analysis. Antibiotics were extracted by solid-phase columns at various conditions. Finally, the prepared samples were measured by a high-performance liquid chromatography system and ultraviolet detector. Results: The effect of pH on the percentage recovery was significant. At pH = 7 and concentration of 100 µg l-1 the highest recovery rate for vancomycin and imipenem were obtained 86% and 79%, respectively. Linearity of calibration curves for vancomycin and imipenem was obtained 0.9778 and 0.9887, respectively. Precision (RSD) of the calibration curve slopes was obtained about 5%. Limit of detection (LOD) of 6 and 3 and limit of quantification (LOQ) of 16 and 11 were obtained for vancomycin and imipenem respectively. Vancomycin and imipenem were measured in hospital wastewater in 72 and 66% of the samples, respectively. The highest concentration that measured for vancomycin and imipenem were 83.57 and 22.4 µg l-1, respectively. Average concentrations of vancomycin and imipenem were obtained 23.19 and 8.7 µg l-1, respectively. Vancomycin was found in 2 samples64 collected from the inlet that the mean concentration was 7 µg l-1. In the outlet of wastewater treatment plant, vancomycin was at concentrations lower than the LOD. Average concentrations of imipenem in four samples from the inlet were 5.5 µg l-1 and in the outlet only was detected in one sample in the concentration of 4 µg l-1. Conclusions: The results show that the method used to extract and measure of antibiotics was an accurate and simple method according to the validation results. Large difference between the concentrations values are due to fluctuations in the quality and quantity of wastewater that is discharged from the hospital. Hospital wastewater mixing with municipal wastewater will reduce the concentration of the compounds. Therefore, in this study the antibiotic concentrations decreased in the municipal wastewater. According to the findings, the removal efficiency of the wastewater treatment plant is not determinable, but residuals of the both antibiotics were found in the plant effluent.