As a result of their widespread use in various high-tech applications, Rare Earths and Yttrium (REY) have become microcontaminants in freshwater systems. However, their biogeochemical behavior, particularly their uptake by aquatic organisms, remains poorly understood. In this study, we investigated the distribution of REY in different soft tissues and shells of freshwater bivalve A. anatina, along with REY levels in ambient water from the Danube River in Hungary and the Vistula River in Poland, as well as in their potential food sources. Regardless of the origin of the samples, all compartments of the mussels exhibit very similar shale-normalized REY patterns. Despite Gd contamination of the river waters from MRI contrast agents, no anthropogenic positive Gd anomalies were observed in any mussel sub-samples. This suggests that anthropogenic Gd from MRI contrast agents may not be bioavailable in freshwater, or that REY from ambient river water do not significantly contribute to the REY uptake of freshwater mussels.
Compared to ambient water, bivalves accumulate REY, particularly Ce and light REY. However, REY concentrations in mussels are generally lower than those in their potential food sources, with minor fractionation along the REY series, except for preferential uptake of La and Y. Comparison of shells and tissues does not indicate any major fractionation during transfer within the mussels or shell formation. Mussel shells, therefore, may serve as convenient indicators for environmental monitoring of REY, without significant interference from vital effects.