An integrated approach to study pharmaceuticals and their microbial transformation products: formation and environmental behavior in water/sediment systems

Pharmaceuticals are emerging organic micropollutants that are frequently detected in the aquatic environment. While information on their environmental occurrence is substantial, knowledge gaps exist with respect to their environmental transformation. This licentiate thesis focuses on this research deficit by (1) providing and applying tools for identifying biotransformation products, and (2) investigating the behavior of pharmaceuticals and their transformation products (TPs) in two different experimental systems. Study I established a data-processing method based on peak detection, time-trend filtration and structure assignment, and provides an efficient and reliable way for TP identification. Water/sediment tests were carried out with 9 pharmaceuticals. The method for identifying TPs is based on accurate mass data obtained from high resolution mass spectrometry and a comprehensive data-processing workflow. In total, 16 TPs were identified, 11 of which were confirmed by reference standards. Five of the TPs showed a continuous accumulation over the entire incubation period of 35 days. Study II aimed at studying the influence of water/sediment interactions on the environmental behavior of pharmaceuticals and their TPs. An artificial streaming channel was applied to simultaneously determine the concentrations of parent pharmaceuticals and key TPs in both surface water and sediment pore water under defined hydraulic conditions. All pharmaceuticals dissipated from the test system. The benefit from simultaneously analyzing parent compounds and TPs can be illustrated with carbamazepine, which is generally reported to be persistent. In study II, carbamazepine dissipated continuously from the test system, and the formation of a TP shows that this dissipation can be attributed to microbial biotransformation. The results also indicate that transformation predominantly occurs in the hyporheic zone, but also that TPs can be transported back into the streaming channel. This thesis confirms the crucial role of the hyporheic zone for the elimination of organic micropollutants from rivers and streams. Moreover, the developed workflow for TP identification provides opportunities to efficiently identify TPs for additional micropollutants in laboratory and field studies. In future work, we will study the influence of hydraulic conditions on transformation kinetics and formation of characteristic TPs, and we will extend the work to additional pharmaceuticals. Moreover, we will test the applicability of using TPs as indicators for characterizing ongoing biotransformation in field settings, thereby providing a more efficient way of characterizing the environmental fate of pharmaceuticals.