Occurrence and seasonal variation of pharmaceutical residues of emerging concern in South African surface waters

Pharmaceutical residues in aquatic environments pose a growing concern, mainly driven by the increasing use of medications. This study investigated the occurrence of four pharmaceutical compounds, namely azithromycin (AZI), prednisolone (m-PRD), prednisone (PRD), and dexamethasone (DEX) in surface waters across eight different sites in the Free State Province, South Africa, during summer and winter 2024. Samples were collected from upstream, downstream, and the wastewater point of discharge at each site. Using a validated liquid chromatography-mass spectrometric (LC-MS) method, all target analytes were detected, with DEX (41.79 µg/L) and AZI (19.32 µg/L) recording the highest mean concentrations in summer and winter, respectively. Moreover, AZI showed the highest detection frequency across all sites and seasons. Spatial variation was evident, with concentrations of analytes differing among upstream, downstream, and points of discharge, revealing the influence of wastewater input and other site-specific factors. The consistent presence of these pharmaceutical residues in surface waters pinpoints a potential risk to aquatic ecosystems and raises concerns about human health implications resulting from the long-term environmental presence of these compounds. The findings underscore significant seasonal fluctuations in pharmaceutical residue levels, highlighting potential risks to aquatic ecosystems and public health. These results call for targeted monitoring efforts and evidence-based regulatory frameworks to mitigate contamination and guide sustainable water resource management in South Africa.