Detection of active pharmaceutical ingredients in surface water polluted by an informal settlement.

The presence of active pharmaceutical ingredients (APIs) and other pollutants in rivers receiving runoff from informal settlements remains poorly understood, particularly in peri-urban environments with limited wastewater treatment infrastructure. This study aimed to monitor the presence of APIs and other pollutants in the Stiebeuel River, which receives polluted runoff from an informal settlement (estimated population of 8100) in the Western Cape, South Africa. A discrete automatic sampler was used to capture temporal variations in pollutant concentrations over 24 h in April and May 2024. The study was conducted during the dry season due to the reduced dilution effect of rainfall and runoff. Samples were analysed for physical and chemical parameters, including ammonia, orthophosphate, sulphate, total organic carbon, and E. coli, as well as 14 targeted APIs and lifestyle markers using ultra-performance liquid chromatography-mass spectrometry. The results indicate elevated concentrations of nutrients and E. coli, with peak pollutant loads occurring between 10:00 and 16:00, most likely associated with heightened human activity in the settlement. API analysis confirmed the presence of 11 compounds from a targeted list of 14, including antiretrovirals (efavirenz, nevirapine, ritonavir), antibiotics (trimethoprim), and analgesics (paracetamol, diclofenac), among others. These findings suggest that informal settlements discharge elevated concentrations of nutrients and act as a source of API pollution with potential downstream impacts for users and aquatic ecosystems. The findings highlight the need for improved water quality monitoring in South African catchments impacted by informal settlement runoff.