Behavior of geogenic and anthropogenic rare earth elements and yttrium in a natural freshwater ecosystem

Although considered emerging contaminants and critical raw materials, the biogeochemical behavior of geogenic and anthropogenic rare earth elements and yttrium (REY) in freshwater systems remains poorly constrained. Here we provide high-quality, multi-trophic REY data from two freshwater ecosystems along the Rhine River, one impacted by anthropogenic REY and one unaffected. Similar to previous studies on estuarine and marine systems, REY concentrations decrease with trophic level, necessitating matrix separation and preconcentration to provide high-quality REY data for ultralow-concentration samples. Among fish tissues, gills and livers show the highest REY concentrations, consistent with detoxification and/or sequestration functions. Additionally, these large concentration differences between and within biota highlight the need to thoroughly record baseline REY levels in natural ecosystems. Despite differences in REY concentration, shale-normalized REY patterns are closely similar across organisms, suggesting that REY signatures are largely conserved along the food web. This allows them to be used for biogeochemical fingerprinting. While the anthropogenic Gd from macrocyclic contrast agents in the Rhine River it is not bioavailable, the anthropogenic La derived from the production of fluid catalytic cracking catalysts is taken up by organisms and can be traced along the food chain. Mussel shells record temporal changes of La levels in ambient water, making them promising long-term bioarchives for REY monitoring and contamination tracking.