Rare Earths and Yttrium (REY) are widely used in many domains, resulting in anthropogenic input into the environment. However, still little is known about their uptake and bioavailability towards aquatic organisms.
We studied REY bioavailability by quantifying their concentrations in the aragonitic shells of Corbicula fluminea, which are precipitated from the extrapallial fluid (EPF) of the mussel. Both shells and ambient water samples were collected from the Elbe and Weser rivers which are known to carry anthropogenic gadolinium (Gd) from Gd-based contrast agents (Gd-CAs) applied in magnetic resonance imaging. The shells were grouped according to their size, meticulously cleaned, acid-digested and pre-concentrated before ICP-MS measurement. Analytical quality was monitored by using REY-poor reference material JLs-1.
Total REY concentrations in the shells decrease with increasing shell size, indicating that REY uptake occurred most rapidly during the juvenile age of mussels. Shale-normalized REY patterns show a continuous increase from light REY (LREY) to heavy REY (HREY) and a slightly inverse V-shape for shells from the Elbe and Weser rivers, respectively. Compared with the 0.2 µm-filtered waters from the same locations, the shells show between 2 to 4 magnitudes higher total REY concentrations. Despite significant anthropogenic Gd enrichment in the river waters, no Gd anomaly is observed in the shells suggesting long environmental half-life and poor bioavailability of the Gd-CAs. Partition coefficients between shells and water reveal a preferential uptake of LREY over HREY in mussel shells. These observations complement and corroborate the results of previous research on shells from the Rhine River.