Quantification and distribution of pharmaceuticals and their human metabolite conjugates in a municipal wastewater treatment plant
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Pharmaceuticals have the potential to persist environmentally through constant anthropogenic input via wastewaters. Toxic effects, both acute and chronic, can be elicited on non-target organisms within the aquatic environment depending on both species sensitivity and chemical class. Overall toxicity can be due to not only parent compounds but transformation products (TPs) as well. It was hypothesised that levels of pharmaceutical TP conjugates would rival those of the parent compounds within a major point source of pharmaceuticals (i.e. wastewater). This thesis successfully developed quantitative methods, for the first time, for four different classes of pharmaceuticals and three different types of conjugate TPs using weak anion exchange solid phase extraction in conjunction with liquid chromatography-tandem mass spectrometry for wastewaters and associated solids; and was validated using the North End Waste Pollution Control Centre located in Winnipeg, Canada. A three-month pilot experiment was conducted using these methods and highlighted the levels of acetaminophen, propranolol, sulfamethoxazole, and thyroxine, in addition to associated conjugate TPs: acetaminophen sulfate, propranolol sulfate, N-acetyl sulfamethoxazole, sulfamethoxazole glucuronide, thyroxine glucuronide. Four different stages of wastewater processing were analysed (primary effluent, secondary effluent, mixed liquor, and final effluent), and levels in aqueous and solid phases assessed. Overall, acetaminophen was rapidly attenuated from primary to secondary effluent (>99%), propranolol and thyroxine persisted without any notable attenuation, and sulfamethoxazole were attenuated by approximately 67-78% from primary to secondary effluent; however the ratio of the three compounds remained consistent across treatments. Several batch bioreactor experiments using primary and secondary effluent, were conducted to backstop what was seen environmentally. In addition, plausible mechanisms for temporospatial variation (i.e. removal/ attenuation) were inferred. For the first time, bioreactor results showed concomitant effects on TP levels in the laboratory that were seen environmentally. In conclusion, levels of conjugates across all four classes of compounds, whether an acid, base, or zwitterion, did indeed rival those of the parent compounds within wastewaters. Sorption of ionisable pharmaceutical conjugates seems to be driven by hydrophobicity in the presence of substantial organic matter. Thus, dependent on pedoclimatic conditions, exposure levels and ostensibly the fate of these pharmaceutical TPs can vary.
Wastewater, Mass spectrometry, Pharmaceuticals, Metabolites