Pharmaceuticals in sewage: Sources, concentrations and degradation

Abstract

Pharmaceuticals have been detected in the environment at low concentrations. A major source of these pharmaceuticals is sewage effluent due to the failure of conventional sewage treatment processes to remove them. Amongst other sources of pharmaceuticals in sewage water, unused and expired medications and those returned to community pharmacies that are improperly disposed of can be a significant source. Currently, there is little data on the overall lifecycle of pharmaceuticals from their prescription or sale to the environment.

Aims: The aims of this thesis were (1) to determine whether community pharmacies are sources of pharmaceuticals in sewage, (2) to detect and identify pharmaceuticals in New Zealand sewage and (3) to determine whether their removal from wastewater can be chemically enhanced. Methods: To establish how community pharmacies dispose of expired, unused and unwanted medications, a questionnaire was sent to 500 community pharmacies across New Zealand asking how they disposed of various types of dosage forms. The questionnaire also asked whether pharmacists thought a state-run disposal and destruction system for unused pharmaceuticals should be implemented. To determine pharmaceuticals in wastewater, samples of sewage influent and effluent were collected from a single sewage treatment facility and analysed for the presence of selected pharmaceuticals by liquid chromatography-tandem mass spectrometry (LC-MS/MS). To determine whether sewage treatment can be chemically enhanced, advanced oxidation and reduction processes (AORPs) were assessed for their ability to reduce the concentrations of three pharmaceuticals [oseltamivir (OS), trimethoprim (TMP) and enoxacin (ENX)] in wastewater. These AORPs included degradation by UV irradiation alone and in the presence of hydrogen peroxide (H2O2), a combination of hydrogen peroxide and iron (II) (the photoFenton process) and the photocatalyst, titanium dioxide (TiO2). In addition, the ability of natural organic matter (NOM) in the environment to enhance the removal of pharmaceuticals in water was investigated using the excited triplet state of benzophenone as a surrogate for NOM. Key Findings: Many pharmacists reported the disposal of liquid medications and Class B controlled drugs by flushing down the sink (44.7%, n = 338 and 58%, n = 287 respectively) indicating that community pharmacies are a source of pharmaceuticals in wastewater. Analysis of wastewater detected and identified seven pharmaceuticals (bezafibrate, carbamazepine, fluoxetine, metoprolol, paracetamol, sulfamethoxazole and trimethoprim) in samples of sewage influent and effluent but their concentrations were either too low to be quantified or were not significantly different from their respective limits of detection. In regards to the removal of pharmaceuticals from water, AORPs were shown to be effective at degrading OS, TMP and ENX, with H2O2 and TiO2 generally enhancing photodegradation. Most of the photodegradation processes obeyed first-order kinetics. A second-order kinetic model was more appropriate at describing the irradiation of ENX by UV alone, the UV/H2O2 treatment of TMP and the photoFenton treatment of TMP at pH 3. While the first-order degradation rate constant for OSP was significantly different between irradiation by UV alone and treatments involving the hydroxyl radical, no significant differences were observed for ENX between such treatments. However, no photodegradation was observed for TMP when irradiated by UV alone and none of the three compounds were observed to completely mineralize in the irradiation timeframes (30 min) studied. None of the selected pharmaceuticals studied were conclusively identified as quenchers of the benzophenone triplet state. Conclusions: The discharge of unused pharmaceuticals in wastewater poses a risk to the environment. While AORPs are effective to some extent at removing them from water, their persistence in the environment may be prolonged as there is some indication that NOM does not assist in their UV-catalysed degradation. However, the quenching data were very variable and only tentative conclusions can be drawn regarding the environmental persistence of the pharmaceuticals studied.