Contamination of surface water resources by residues of selected pharmaceuticals repurposed for Covid-19 treatment: a case study in Mangaung Metropolitan Municipality, Free State Province of South Africa

Covid-19 drug residues of azithromycin, prednisone, prednisolone, 20α-hydroxy prednisone metabolite and dexamethasone were examined using HPLC MS in water and sediment samples of surface water resources. The pseudo-partitioning coefficient (P-PC) and the groundwater ubiquity score (GUS) were used to determine the fate of the Covid-19 drug residues. Principal component analysis (PCA) and Spearman’s rho non-parametric analysis statistical methods were used to determine the significance and correlation amongst the Covid-19 drugs and their sources. Azithromycin, prednisolone, prednisone, dexamethasone, and the 20α-hydroxy prednisone metabolite residues were detected at maximum concentrations of 3.7630, 0.0563, 0.0069, 0.0050 and 0.008 µg/mL, respectively, in water samples. In sediments, only azithromycin and prednisone residues were detected at maximum concentrations of 0.56764 and 0.00424 µg/g. There was a statistical difference ( p-value <  0.05) and a direct correlation ( rho  > 0.5) between azithromycin and dexamethasone, and also a statistical difference ( p-value <  0.05) and a direct correlation ( rho  > 0.5) between prednisolone with prednisone and the 20α-hydroxy prednisone metabolite. Significant loadings (component factor > 0.5) for PCA were observed for azithromycin, prednisolone and prednisone, attributing their pollution sources to wastewater treatment facilities (WWTFs), livestock farming, agricultural runoff, clinics and hospitals. Azithromycin and dexamethasone presented high leaching potential (GUS > 2.8), whereas azithromycin was the only drug with a high P-PC of 11.315. In conclusion, there is an occurrence and accumulation of the selected Covid-19 drug residues in surface water resources. An investigation of the Covid-19 drug residues and their metabolites on terrestrial land, and also of informal settlements as sources of pollution to water resources by Covid-19 residues is essential.