Occurrence of selected antibiotics and antiretroviral drugs in Nairobi River Basin, Kenya

In this paper, we investigated the occurrence of three antibiotics (sulfamethoxazole, trimethoprim and ciprofloxacin) and three antiretroviral (lamivudine, nevirapine and zidovudine) drugs in the Nairobi River Basin, Kenya. The analytical procedure involved extraction using solid phase extraction followed by liquid chromatography–electrospray ionization tandem mass spectrometry (SPE–LC–ESI–MS/MS). In this study, 40 sites were selected for sampling, including 38 sites along the rivers and 2 wastewater treatment effluent sites. All the studied compounds were detected with sulfamethoxazole having the highest detection frequency of 97.5% and ciprofloxacin had the lowest at 60%. The results showed that the concentration of the drugs increased in highly populated regions especially within the informal settlements. The maximum (median) concentrations in the river waters for sulfamethoxazole, trimethoprim, ciprofloxacin, lamivudine, nevirapine and zidovudine in ng/L were 13,800 (1800), 2650 (327), 509 (129), 5430 (1000), 4860 (769), and 7680 (660), respectively. The maximum concentrations in the river waters were generally higher than those of the wastewater treatment plant effluents signifying that the rivers are substantially contaminated by domestic wastewater. The environmental risk was evaluated by calculating the risk quotients (RQs) for algae, daphnia and fish based on the maximum and median concentrations of the analytes in the river basin and was expressed as the ratios of measured environmental concentrations (MEC) to predicted no effect concentrations (PNEC). The RQs ranged from 0 to 507.8 and apart from lamivudine that had a low RQ, all the other analytes had RQ > 1 at maximum and median measured concentrations for at least one taxonomic group. The high RQs are indicative of possible adverse ecological effects and calls for corrective and mitigation strategies.