Surface water quality contamination by selected residues of pharmaceuticals repurposed for Covid-19 treatment

Abstract Residues of pharmaceuticals are gradually accumulating in surface water resources because of the disposal of wastewater effluent. For the present study, four surface water resources (rivers and streams) that receive wastewater effluent discharge were selected as the study sites in Bloemfontein, South Africa. Coronavirus, 2019 (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 physicochemical characteristics of the assessed sites were also determined and assessed against the world health organisation (WHO) and environmental protection agency (EPA) limits as well as the overall water quality index using the weighted arithmetic water quality index (WWQI). 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. Maximums of Ammonia (NH3) (792.7 mg/L) and the chemical oxygen demand (COD) (846 mg/L) were found to be non-compliant with the EPA and WHO standards, while the dissolved oxygen (DO) presented a low 0.11 mg/L. An unacceptable water quality status or score for all the 4 assessed sites was observed deeming the water excessively polluted. Azithromycin, prednisolone, prednisone, dexamethasone, and the 20α-hydroxy prednisone metabolite residues were detected at maximum concentrations of 3.763, 0.0563, 0.0069, 0.005 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, as well as 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 plants (WWTPs), 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 21.25. 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.