Das Projekt "Wege und Geschwindigkeiten der Abfuehrung von Spurenmetallen im Oberflaechenwasser von Seen: Untersuchung mittels umweltfreundlicher radioaktiver Tracer" wird vom Umweltbundesamt gefördert und von Universite de Geneve, Institut F.-A. Forel durchgeführt. We propose a study of trace metal removal from lake surface water using radionuclide tracers. Particular attention will be given to the role of the colloidal fraction in removal process. Particle-reactive radioisotopes are useful tracers for studying transport processes and scavenging by settling particles in aquatic environments. Using a number of radionuclides with different 'reactivity' in respect to particle surfaces, we can consider them as surrogates for a number of metals. The objectives of the project are the following: 1. Laboratory batch experiments with radioactive tracers (7Be, 234Th, 210Pb, 210Po) to determine the relative affinity of these tracers to natural particles. 2. Further development and comparison of sinkable particle and colloid separation techniques with a focus on tangential flow filtration. 3. Test of applicability of multi-tracer methods for investigation of pathways, removal mechanisms and characteristic time scales in the epilimnion of Lake Geneva. 4. Modelling of radionuclide behaviour observed in the field (point 3) using parameters determined in experiments (point 2). Leading Questions: -What is the relative affinity of radioactive tracers (7Be, 234Th, 210Pb, 210Po) to natural particles and colloids? - How it compares to affiniy of trace metals and metallic pollutants? - Is coagulation of colloids a rate-determining step in removal of metals from epilimnion? - How removal rate relates to the trophic state?