Spectroscopic and chromatographic analysis of Nevirapine, Lamivudine and Zidovudine anti-retroviral compounds in wastewater samples from selected wastewater treatment plants, Cape Town

Abstract

The HIV/AIDs pandemic is still prevalent and the consumption of antiretroviral (ARV) compounds is on the increase. After ingestion, the compounds are not completely consumed in the human system, they flow as parent compounds or metabolites into wastewater treatment plants (WWTPs) via urine and faeces. Unfortunately, the compounds are not completely removed in WWTPs and subsequently end up in aquatic ecosystems. The occurrence of these compounds in aquatic ecosystems constitute a health risk to aquatic life, human and the environment at large which requires adequate removal approach. In South Africa, three pharmaceuticals compounds called lamivudine (3TC), zidovudine (AZT) and nevirapine (NVP) are commonly used for the treatment of HIV/AIDs. This study collected monthly grab wastewater samples from two WWTPs in Cape Town metropole, South Africa, from autumn of 2018 to autumn of 2019. Raw influent (RI), final effluent before UV treatment (BUVT) and final effluent after UV treatment (AUVT) samples were collected from WWTP 1, while final effluent (FE) was collected from WWTP 2. To assess the prevailing physical and chemical conditions of the wastewater from the two plants, ten physicochemical parameters from the wastewater samples were evaluated using approved standard methods. Also, a UV-visible spectrophotometer was validated and used to determine residues of 3TC, AZT and NVP in the wastewater samples from both plants. Two novel advanced oxidation processes (AOPs) namely sunlight(UV)/Cl2 and sunlight (UV)/KMnO4 were developed. Operating parameters/conditions such as solar irradiance, pH, reaction time and oxidant to analyte ratio (OAR) were optimised and used to degrade the three pharmaceutical compounds in Milli-Q water, while the residual concentrations were measured by UV Visible spectrophotometer. The optimised method was applied to degrade the three target pharmaceuticals residues in real wastewater samples from both plants and monitored with high-performance liquid chromatography (HPLC). The result of the physicochemical investigation in the two plants showed that temperature, pH and SO42- levels comply with the regulatory limit for wastewater discharge by both national (Department of Water Affairs and Forestry (DWAF), South Africa and international (United State Environmental Protection Agency (USEPA) regulatory standards. Nevertheless, the remaining seven parameters evaluated did not completely conform with the set limits prescribed by both bodies. Method validation confirmed that the UV-vis spectroscopy method is an accurate, precise, quick and less expensive way of determining the selected ARVs in wastewater samples. Similarly, the result emanating from the spectroscopic determination of the three pharmaceutical compounds in the AUVT sample in WWTP 1 and FE in WWTP 2 showed that 3TC ranged between (11.80 – 52.90 µg/L), AZT (0.90 – 66.98 µg/L) and NVP (54.70 – 207.70 µg/L). The percentage removal of the ARVs compounds in WWTP 1 was found to be 70%, 65% and 55% for AZT, 3TC, and NVP, respectively. Though our target pharmaceutical compounds are not yet regulated; the results however indicated that effluents originating from the two WWTPs are probable sources of ARVs and physicochemical pollutions to the receiving water bodies, which require adequate improvement of the WWTPs operations to guarantee safe effluent discharge. The HPLC method used was able to resolve the three compounds of interest within 7 minutes, and the validation of the method showed that the method is suitable for the analysis of 3TC, AZT and NVP in wastewater samples. For the degradation studies,the optimised conditions for (sunlight)UV/chlorine process was at pH 7, OAR 7:1, solar irradiance 250 ± 25 mW/m2,and 90 minutes and the % removal recorded were 3TC: 7.31 ─ 70.79%, AZT: 29.64 ─ 91.69% and NVP: 15.60 ─ 67.77%. For UV/KMnO4, the optimised conditions were pH 5, OAR 7:1, solar irradiance 250 ± 25 mW/m2,and 45 minutes and the % removal recorded ranged between 2.70 ─ 100.00%, 6.48 ─ 100.00% and 15.41– 100.00% for 3TC, AZT and NVP. The % removal obtained in both methods were higher than those recorded for the two control experiments which involve chlorine alone or KMnO4 alone and sunlight (UV radiation) alone.