Reactivity and fate of technology critical elements in three contrasting river systems

The reactivity and fate of Technology Critical Elements (TCEs) in rivers are still widely unknown. We present yearly monitoring results for Rare Earth Elements (REEs) and less known TCEs such as tellurium (Te) and Thallium (Tl), for three contrasting German watersheds: the Rhine, the Neckar and the Danube rivers. Monthly samples of water (0.45 vs 0.02 µm) and suspended particulate matter were analysed directly and after digestions via ICP-MS (iCAP series, Thermo®). Results show contrasting behavior between watersheds. For instance, only the Neckar River shows increased downstream transport of REEYs in the dissolved phase, reflecting the impact of dams along its course. In contrast, only the Danube River shows a mixed signal between geogenic and anthropogenic Gd, the latter disappearing completely during flood conditions. In any case, flood conditions enhance an overall transport of REEs in the truly dissolved phase for all rivers, increasing the amount released into the system, decreasing the log Kd values and causing a characteristic Tm negative anomaly. The opposite occurs for Tl and anthropogenic Gd, suggesting for Tl an anthropogenically dominated regime, especially at the Neckar and Danube rivers. All this information provides insights for developing scenarios for potential risk assessment of current and future anthropogenic releases of TCEs in aquatic environments.

Acknowledgements: This work was funded as part of the Excellence Strategy of the German Federal and State Governments. The authors also acknowledge the extensive contribution of LUBW (Germany) and AUE (Switzerland) for the collection of water and suspended sediment samples.