Pharmaceuticals of emerging concern within a transboundary river basin: spatial, ecological risks patterns and human health risks assessments

Abstract

ABSTRACT In this study, the environmental occurrence of selected pharmaceutical compounds widely used during the COVID-19 pandemic (prednisone, prednisolone, dexamethasone, and azithromycin) was investigated. A solid-phase extraction-liquid chromatography–mass spectrometry method quantified these analytes in surface water samples collected from eight sites within the Orange–Senqu River Basin in the Free State Province, South Africa. Sampling was conducted across summer and winter to evaluate spatial and seasonal variations. Measured concentrations ranged from below the limit of detection (<LoD) to 41.79 μg L−1 in summer and 19.32 μg L−1 in winter, with azithromycin being the most frequently detected compound across sites. Seasonal analysis showed no statistically significant differences in azithromycin concentrations (p > 0.05), indicating persistent year-round inputs. Ecological risk assessment using risk quotient (RQ) analysis indicated low to moderate ecological risks, with RQ values for azithromycin ranging from 0 to 0.39 depending on the predicted no-effect concentration (PNEC) applied. Localised ecological risk hotspots were associated with dexamethasone concentrations near wastewater discharge locations. Human health risk assessment suggested generally low risk through drinking water exposure pathways. Nevertheless, the persistent detection of these pharmaceuticals highlights the need for continuous environmental monitoring and improved wastewater management strategies.