Fate of pharmaceutical micro-pollutants in Lake Tegel (Berlin, Germany): the impact of lake-specific mechanisms

Pharmaceuticals in the aquatic environment have become important because of the risk of harmful effects to ecosystem and drinking water abstraction. This is also the case in shallow dimictic Lake Tegel, located in the city area of Berlin, Germany. Here, drinking water is produced via bank filtration and artificial groundwater recharge, and concurrently, a substantial anthropogenic load takes place by micro-pollutants from a municipal wastewater treatment plant. The measured mean daily loads of 260 g d−1 carbamazepine, 180 g d−1 diclofenac and 60 g d−1 sulfamethoxazole results in the highest so far reported concentrations from natural waters, which are used as a drinking water resource. In the present study the spatial horizontal and vertical distribution and elimination of these three pharmaceuticals are quantified with the help of high-resolution sampling in Lake Tegel and its entire major in- and outflows. Monthly mass balances are modelled and substance-specific zero-order elimination rates are derived. Diclofenac showed the strongest elimination and revealed a significant seasonality with 50 % elimination in winter, and 95 % in summer. Elimination of carbamazepine was about 40 %; sulfamethoxazole did not degrade at determinable rates. Based on a basic plug-flow approach, a pseudo first-order elimination rate for diclofenac in summer (0.058 d−1, half-life 12 days) was calculated from horizontal concentration gradient. Apart from presenting the current state of pharmaceuticals pollution in Lake Tegel, results demonstrate the importance of lake-specific mechanisms, such as inflow–outflow balances and seasonal density stratification for the transport of micro-pollutants.