Pharmaceuticals are of increasing concern due to their high usage, ubiquitous distribution in the aquatic environment, and potential to exert adverse effects on the ecosystem. They are released from wastewater treatment plants and can thereafter undergo transformation processes in surface waters. Microbial degradation in river sediments is considered a highly significant process for transformation of pharmaceuticals. The overarching objective of this project is to improve the understanding of the environmental fate of pharmaceuticals in rivers, with specific focus on water-sediment interactions and formation and behavior of transformation products. The project integrates transformation product identification and parent compound/transformation product fate determination, using a range of experimental setups from batch experiments in the lab to extensive field studies.