Rare earth elements and yttrium in naturally grown duckweeds: a pathway into the food web

Rare Earths and Yttrium (REY) have become pivotal constituents of many high-technology products and processes. Their widespread use has led to a growing release of (“anthropogenic”) REY into the environment and hence rising concerns about their (bio)geochemical and (eco)toxicological behaviour. Yet, information on REY transfer, fractionation and bioaccumulation and -magnification in the food web is still scant. Here, we present REY data for naturally grown duckweeds and ambient waters. Duckweeds are small, rapidly-growing macrophytes inhabiting many lentic water bodies worldwide. Duckweed is increasingly used as protein-rich animal feed and food supplement for vegans. The REY concentrations of duckweeds are in the µg/kg range (dry matter) and exceed those of ambient waters by several orders of magnitude, revealing strong bioaccumulation. Their shale-normalised (SN) REY patterns are rather flat and show little variation regardless of sampling site and season. By contrast, the REYSN patterns of all 0.2 µm-filtered water samples are characterised by an increase from light REY (LREY) to heavy REY (HREY) and some show large anthropogenic positive GdSN anomalies. Such anomalies have become common in Germany and can be attributed to the application of Gd-based contrast agents (Gd-CAs) in magnetic resonance imaging. The absence of anomalous Gd enrichment in all duckweed samples suggests that Gd-CAs are not incorporated by these macrophytes but corroborates their conservative behaviour in the environment. Moreover, partition coefficients between duckweeds and ambient waters show that the duckweeds preferentially incorporate LREY over HREY, possibly due to stronger complexation of HREY with dissolved ligands.