Removal efficiencies and environmental risk assessment of selected pharmaceuticals and metabolites at a wastewater treatment plant in Pietermaritzburg, South Africa

This research study critically evaluates the concentrations of selected pharmaceuticals found within wastewater and at various stages within a selected wastewater treatment plant. The study further investigates the effects of seasonal variation, between wet and dry months, on the removal of target analytes. To the best of the authors' knowledge, ivermectin in wastewater has not been investigated in South Africa. The methodology used was extraction of the wastewater samples using solid phase extraction with Oasis HLB cartridges followed by analysis on a liquid chromatography-mass spectrometer. As expected, analyte concentrations were observed to decrease as wastewater went through the treatment process with the greatest reduction in concentrations observed between secondary effluent and maturation samples, which could be indicative of photodegradation of compounds. Influent concentrations of analytes ranged from 0.008184 to 1.243 mg L^-1 while maturation river concentrations ranged from not detected to 0.9286 mg L^-1. Removal efficiencies ranged from 7.70 to > 99.99% of analyte removed. Significant differences in removals were observed between the wet and dry seasons experienced within the province. Environmental risk assessment ratios ranged from 0.0863 to 10.5 × 10⁸. Ratios for metformin and valsartan were well below 1, indicating that they would not be of environmental risk. While ratios for ivermectin were substantially high, ranging from 25.4 × 10⁷ to 10.5 × 10⁸ indicating that it is of severe environmental risk and is of significant concern. Generally, the analyte concentrations quantified within influent samples were higher than effluent samples which is indicative of the treatment process being able to partially remove some of the analytes. Risk assessment ratios suggest high risk of selected pharmaceuticals which are of environmental concern.