Based on the investigations at biofilms and the zoo-plankton of German rivers and the results of the sediment- and water samples from the Szamos/Tisza longitudinal profile a methodology for biofilm analyses using the micro digestion procedure and the TXRF analyses is to be adapted. For identifying substantial biochemical processes of heavy metal accumulation on biofims and zoo-plankton reactor tests must be developed, planned, executed and analyzed. A training with the high sophisticated technical equipment and procedures is required to guarantee high quality data. Mathematically statistical procedures of the experimental design, as they are in use in the research group of water chemistry, will be tested to optimize the random conditions for the reactor tests. An emphasis will be the leaching procedure of Tisza and Szamos sediments. The leached water will affect the biofilms and zoo-plankton in biofilm reactors. In such a way maximum accumulation rates can be simulated, which occur with sediment re-mobilization and re-sedimentation during flood events. With the knowledge of the leaching experiment an optimized sampling strategy for biofims and zoo-plankton can be developed with non contaminated and contaminated sampling sites in the longitudinal profile of the Szamos and Tisza rivers. The analyzed natural biofilms and zoo-plankton from the Hungarian sampling provide the first indication regarding potential bioaccumulation of these elements within higher aquatic organisms. Additional tests with the biofilm reactors in the concentration range observed at the natural biofilms helps to understand the biochemical processes of element accumulation on biofilms.