Serkan Kulaksiz

• The first comprehensive geochemical dataset of the Rhine River and its major tributaries is provided. The major ion chemistry of the Rhine River and its tributaries is characterized. Natural variation of rare earth elements (REE) with discharge and season, and the effect of catchment geology on the distribution of rare earth elements is discussed. The sources and quantities of known and newly discovered anthropogenic REE are examined. While the presence of anthropogenic gadolinium (Gd) anomalies in the Rhine River has been reported previously, anthropogenic lanthanum (La) and anthropogenic samarium (Sm) anomalies are documented for the first time, both for the Rhine River and natural waters worldwide. Both anthropogenic La and Sm originate from the waste water effluent at a facility producing catalytic fluid cracking catalysts. Ultrafiltration results suggest that anthropogenic Gd is not particle-reactive and is exclusively present in the truly dissolved REE fraction, while the anthropogenic La and Sm are present in both the truly dissolved and the nanoparticulate phase. In parts of the Rhine River, anthropogenic REE concentrations are an order of magnitude higher than background concentrations for three (La, Sm and Gd) of the fourteen REE. Due to the high toxicity of REE, this may pose a threat to the ecosystem, especially given the lack of studies that focus on low-dosage long-term exposure. With the demand for REE and the number of REE applications rapidly increasing, more anthropogenic REE are expected to enter the environment in the near future. Within the short duration of this study alone, two anthropogenic REE anomalies have been documented. The current situation of REE contamination may well be only a prelude to what will soon happen with other emerging contaminants.