Rare Earth and Yttrium in tissues and shells of mussel from the Danube River and its tributaries

Due to their numerous applications in various high-technology products, Rare Earths and Yttrium (REY) have become microcontaminants of freshwater systems. Nevertheless, their biogeochemical behaviour, especially their uptake by aquatic organisms is still poorly understood.

Here, we report REY concentrations in the shells of four different mussel species, and in the tissue and shells of three Anodonta anatina mussels, and in the respective ambient water from the Danube River and some tributaries. The shells were grouped according to their sizes and meticulously cleaned, while the soft tissues were dissected and lyophilized. All samples were acid-digested and preconcentrated prior to ICP-MS measurements. Analytical quality was monitored by using certificated reference materials JLs-1 and BCR-668 for shells and tissues samples, respectively.

A size dependency of the REY concentration was only observed for Corbicula shells, corroborating the previous observations at the Rhine River. Shale-normalized REY patterns are similar for all shells and tissues and slightly MREY-enriched. Compared with the 0.2 µm-filtered ambient water, the biological samples show REY concentrations that are between three to five orders of magnitude higher, revealing significant bioaccumulation of REY. The observed preferential uptake of LREY relative to HREY is due to more stable complexation of HREY with dissolved ligands. Despite significant anthropogenic Gd enrichments in ambient water, there are no positive Gd anomalies in the biological samples, suggesting biounavailability of Gd based contrast agents.