The impact of a Wastewater Treatment Works in Southern Gauteng, South Africa on efavirenz and nevirapine discharges into the aquatic environment

There has been growing concern regarding the pollution of the aquatic environment with synthetic organic chemicals. Antiretroviral drugs, such as efavirenz and nevirapine, are pharmaceutical drugs and are referred to as emerging contaminants. Such drugs can be environmentally persistent and may be expected to pose potential risks to drinking water supplies. Sources of pharmaceutical drugs include effluents from Wastewater Treatment Works (WWTPs), hospital and pharmaceutical production facilities and the incorrect disposal of unused and expired medicines. Currently there are no monitoring programs and legislative guidelines for their regulations in South Africa. The aims of this study were firstly to develop a semi-quantitative method to extract and analyse efavirenz and nevirapine in the primary settling tank sludge. Secondly to use that method, and an existing method for liquid wastewater samples, to monitor the concentrations of efavirenz and nevirapine as the wastewater passes through the different stages of purification (anoxic; aerobic; pre and post chlorination) in the WWTP. This was repeated weekly over a period of 4 weeks. Thirdly, to determine if binding of efavirenz and nevirapine to the solids in the WWTP played a role in the removal of these compounds from the WWTP liquid phase. No references to the analysis of ARVDs in WWTP sludge were found in the literature. Grab samples of wastewater and sludge samples were collected from a WWTP (activated sludge treatment process) weekly for 4 weeks. Liquid samples were extracted solid phase extraction, solid samples were extracted using sonication followed by a QuEChERs clean-up. Sample extracts were then subjected to gas chromatography-time of flight mass spectrometry for analyte determination. Efavirenz concentrations entering the WWTP ranged between 5500 to almost 14 000 ng/L. The removal of efavirenz by the WWTP ranged between 27 and 71%. The largest removal occurred in the anoxic zone, smaller amounts were removed in the aerators. Slight increases in efavirenz concentrations were found after chlorination and the final effluent into the river post maturation ponds again were slightly lower. Solids were found to contain efavirenz at concentrations between 17 and 43 mg/kg dried primary settling tank sludge and it is proposed that this binding to the solids is the main mechanism of removal of efavirenz from the wastewater stream as it passes through the WWTP. Although an order of magnitude lower nevirapine concentrations displayed the opposite behaviour and gradually increased through the various stages of purification in the WWTP. Minor fluctuations occurred but the concentrations of nevirapine were higher at the effluent (between 92 and 473 ng/L) than those entering the WWTP. No nevirapine was detected in the PST sludge. The increase in nevirapine concentrations are likely to be the result of the de-conjugation of the hydroxylated metabolites of nevirapine in the WWTP, its resistance to degradation and the lack of binding of the nevirapine to the PST sludge.