Winter accumulation of acidic pharmaceuticals in a Swedish river

In this study, seasonal variations in the concentration profile of four analgesics and one lipid regulator were monitored on their way from a wastewater treatment plant (WWTP) effluent, along a river, and into a lake. From December 2007 to December 2008, water samples were collected monthly (n = 12) from an upstream point, the effluent, four downstream points of the WWTP, and at the point where the river merges with the lake, and the concentrations of ibuprofen, naproxen, bezafibrate, diclofenac, and ketoprofen were determined. The analytical methodology involved solid-phase extraction of the target compounds from water samples followed by liquid chromatography coupled with tandem mass spectrometry for compound separation and detection. The studied pharmaceuticals were found in the effluent at concentrations ranging from 31 to 1,852 ng l−1 depending on the season. In the river and lake, the concentrations were much lower (6–400 ng l−1) mainly due to dilution but also to a season-dependent contribution from natural transformation processes. The mean mass flow of all analgesics was highest during winter while the highest mean mass flow of the lipid regulator bezafibrate was observed in spring. The WWTP is the main source of the target compounds in the aquatic environment. The observed winter accumulation signifies the importance of natural transformation processes, which can only be estimated based on mass flow data, on the fate of pharmaceuticals in the environment.