The pharmaceuticals carbamazepine (CBZ), diclofenac (DCF), phenazone (PNZ), sulfamethoxazole (SMX) and trimethoprim (TMP) as well as the alkaloid caffeine (CAF) were analyzed from June 2017 to May 2018 in the surface water of the River Wietze in 5 campaigns at 14 sampling points. Sampling was performed from the source to the mouth as well as in the main tributaries into the River Wietze and in the effluent of the largest waste-water treatment plant (WWTP). In addition, diurnal variations, homogeneity of the samples and concentrations in rain-water samples were investigated. Further measurements to assess the sinks include inorganic analysis, adsorption measurements, photolysis and hydrolysis were carried out in the laboratory. For caffeine a different concentration level and different concentration patterns were found compared to the pharmaceuticals.
WWTPs were identified as the sole source of pharmaceuticals. In contrast, for caffeine, diffuse sources are predominant, e.g. wet deposition cannot be neglected. The concentrations of pharmaceuticals decrease from the largest WWTP in the upper course of the river to the inflow into the River Aller. Mean
concentrations found across all campaigns at the inflow into the River Aller are (in ng/L): 308 (DCF), 164 (CBZ), 61 (SMX), 22 (PNZ), 15 (TMP), 64 (CAF). Concentrations in the winter months are a factor 2-3 lower compared to summer months. In contrast, the sum of the loads of pharmaceuticals at the inflow
into the River Aller in the autumn/winter months of roughly 100 g/day is found to be about a factor of 2 lower in the spring/summer months.
In summer, diclofenac is photochemically degraded with lifetimes in the range of less than 2 days. Other sinks could not be identified, in the winter months all compounds are found to be stable. The load generated by the WWTPs is therefore (with the exception of diclofenac in summer) practically completely
transferred from the River Wietze to the River Aller.