Optimization of extraction techniques for the isolation and pre-concentration of pharmaceuticals in aquatic environments

Abstract

The occurrence of pharmaceuticals in South African aquatic environments has been reported in several studies. However, most of these reports focused on the occurrence of organic compounds in wastewater and surface water. There are very few studies reporting the presence and concentration of these compounds in seawater and coastal areas. Further, most studies have looked at only on one season. This study focussed on the optimisation of a SPE extraction method using Bond Elut Plexa cartridges for the identification and quantification three nonsteroidal anti-inflammatory drugs (NSAIDs), three antiretroviral drugs (ARVs) and a lipid regulator in coastal area of Durban city, South Africa covering four seasons. The optimised SPE conditions were as follows: 500 mL sample volume and at pH 5.8, 5 and 5 mL as conditioning and elution volumes, respectively. The flow rate ranging from 5 to 10 mL/min 10 and 5 mL/min as sample and elution flow rates. The extracted compounds were qualitatively and quantitatively detected by a high-performance liquid phase chromatographic instrument coupled to a photodiode array detector (HPLC-PDA). The recoveries ranged from 62 -102% with RSD values of 0.56 to 4.68% respectively for the determination of emtricitabine, tenofovir, naproxen, diclofenac, ibuprofen, efavirenz, and gemfibrozil. The analytical method was validated by spiking estuarine water samples with 5 µg L-1 of a mixture containing the target pharmaceuticals and the matrix detection limits (MDL) were established to be 0.62- 1.78 µg L-1 for the target compounds. The optimized method was applied to seasonal monitoring of pharmaceuticals at chosen study sites from winter and spring of 2019 and summer and autumn of 2020.The sum of emerging pollutants (ƩEP) were calculated based on each study site. The influent of the Kingsburgh WWTP (EFK) had the highest ƩEP of 144.88 µg L-1 in winter between the two wastewater treatment plants area in this study. The Northern WWTP influent (INN) had a total ƩEP of 117.11 µg L-1 in autumn, the Kingsburgh WWTP effluent (EFK) had a concentration 63.8 µg L-1 in autumn and a concentration 63.8 µg L-1 in summer and the Northern (EFN) had a total ƩEP of 43.97 µg L-1 in winter. A comparison between UMgeni (UR) and Kingsburgh river (KR) showed that the KR had the highest concentration of total ƩEP of 22.66 µg L-1 and UR with the total ƩEP of 18.3 µg L-1 both in winter and spring, respectively. The seawater EPs Blue Lagoon (BL) had the highest ƩEP of 46.75 µg L-1 in spring, subsequently Warner Beach bottom (WBB), Glen Ashley (GA) and Warner Beach top (WBT) with concentrations of 24.96 µg L-1 in summer, 13.29 µg L-1 in spring and 6.94 µg L-1 in autumn, respectively. Estuarine EPs had concentrations of 37.9 µg L-1 and 20.97 µg L-1 for Warner beach estuary (WE) and UMgeni estuary (UE) in winter. WBE having the highest concentration between the two. This showed a significant variation on the presence of these pharmaceuticals in different season.