Seasonal analysis and environmental risk assessment of selected emerging pollutants in the Vaal River catchment area of South Africa

The presence of pharmaceuticals, especially antibiotics, in aquatic environments can significantly contribute to the rise of antibiotic resistance, presenting a critical global public health challenge. This study investigates the presence of four selected antibiotics and an antiretroviral drug (nevirapine) in the Vaal River in South Africa. Grab samples collected at nine sampling sites across four seasons were extracted using solid-phase extraction and analysed using liquid chromatography coupled with triple quadrupole mass spectrometry. The method detection limits ranged from 0.045 ng L^-1 for trimethoprim to 4.41 ng L^-1 for ciprofloxacin. A general trend of increasing concentrations was observed from upstream to downstream in all seasons, with autumn and winter showing higher concentrations than spring and summer at most sampling sites. The major contributors to the total concentration across all seasons were trimethoprim (3-76%) and nevirapine (4-48%). The environmental risk assessment showed seasonal variability in the ecological risks posed by the targeted pharmaceuticals, with higher risks observed in autumn and winter. Amongst the studied pharmaceuticals, ciprofloxacin exhibited the highest ecological risk, with its risk quotient evaluated to be 11.67. These results call for action to ascertain the sources and stop their release into the river across the catchment area.