In this research project, the fluxes, exposure routes, effects and isotopic fractionation of metals in aquatic and terrestrial ecosystems will be investigated by means of multi-collector ICP - mass spectrometry (MC-ICPMS), a very powerful technique for the determination of isotope ratios. With this innovative technique, the isotopic fractionation of Fe and Zn in plants, about which very little is known until now, will be investigated. The impact of mycorrhizal fungi (root symbionts) on the fractionation of metal isotopes will be identified. By means of tracer experiments with stable metal isotopes, important new information on exposure and internal (tissue-specific and intracellular) distribution of metals in aquatic and benthic invertebrates will be revealed. This will lead to new insights into the mechanisms of metal toxicity and metal bioavailability and to new models that can be used for ecologically relevant and physiologically founded standards and risk assessments for metals.