Occurrence and prevalence of antibiotics in wastewater treatment plants and effluent receiving rivers in South Africa using UHPLC-MS determination

The increased usage of antibiotics over the recent years has led to an increased interest in monitoring their presence in wastewater all over the world. In this study the occurrence of sixteen (16) selected antibiotics (amoxicillin, ampicillin, azithromycin, ciprofloxacin, doxycycline, erythromycin, gentamicin, metronidazole, norfloxacin, ofloxacin, penicillin, sulfamethoxazole, sulfapyridine, sulfamethizole, tetracycline and trimethoprim) were determined in two wastewater treatment plants and two effluent receiving rivers in Northern part of Pretoria, South Africa. Targeted screening and identification of antibiotics was done using ultra high-performance liquid chromatography coupled with mass spectrometry after sample clean-up and pre-concentration using solid phase extraction. The concentrations of the targeted antibiotics detected in influent samples ranged between 0.78 and 96.8 ng mL⁻¹ and those in effluent were between 0.12 and 9.89 ng mL⁻¹. The highest recorded concentrations in all samples were those of doxycycline (30.9–120 ng mL⁻¹) and sulfamethoxazole (2.52–96.8 ng mL⁻¹) in effluent and influent samples, respectively. The concentrations of antibiotics in the rivers receiving effluents were between 0.03 and 72.8 ng mL⁻¹ in upstream samples and 0.008–76.8 ng mL⁻¹ in downstream samples, indicating that there is other source of contaminate to these rivers other than the treatment plants. Risk assessment using the hazard quotients ranged between 0.24 and 889 indicating that the presence of these antibiotics and antibiotic mixtures posed higher ecological risks to aquatic organisms. From the study, it could be concluded that wastewater treatment plants were releasing antibiotics to the environment and posing a risk to the aquatic ecosystem and public health. Therefore, there is a need to research into developing more efficient conventional wastewater treatment technologies that can completely remove antibiotics from wastewater.