Geochemistry of natural and anthropogenic rare earth elements in rivers with emphasis on the Rhine River and its tributaries

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In pristine environments, the rare earth elements (REE) are ideal geochemical tracers. However, anthropogenic gadolinium (Gd) used in contrast agents in computer tomography has been found in numerous rivers worldwide and preliminary samples from the Rhine River even show a strong anthropogenic enrichment of lanthanum (La). The La source is not yet known, but together with the anthropogenic Gd, this La compound is also observed in drinking water. During the proposed project, the distribution of the REE will be studied in the Rhine River and its tributaries. The (seasonal) impact of catchment geology, natural river discharge and anthropogenic input on the REE distribution will be determined during two subsequent low-discharge and high-discharge periods and the source of the unknown La rnicrocontaminant will be located and characterized. This will be complemented by the study of drinking water in major cities along the Rhine River. The proposed project will enhance our understanding of the geochemical behaviour of high-tech elements in the natural environment. Considering that the use of REE in high-tech products and processes is dramatically increasing, the results will also be important for policy-making.