Duckweeds as quasi-hyperaccumulators of rare earths and the biounavailability of Gd-based contrast agents

Duckweeds are widespread macrophytes in lentic waters. These small, fast-growing aquatic plants receive increasing attention as potential food supplement, which makes detailed knowledge of their chemical composition highly important.

The rare earths and yttrium (REY) are pivotal of many enabling technologies causing a constantly growing release of REY into the environment. However, little is known about their transfer from the geosphere into the biosphere. As duckweeds retrieve their elements primarily from ambient water, they are excellent objects for related studies.

We present data for all REY (and some other elements) in naturally grown duckweeds and ambient waters in their habitat. Some of the waters show shale-normalised (SN) REY patterns with pronounced positive Gd anomalies which originate from Gd-based contrast agents (Gd-CAs) applied in magnetic resonance imaging.

Rare earths and yttrium concentrations in the duckweeds strongly exceed those in ambient water and correlate closely with Mn (but not Ca), possibly indicating a common uptake mechanism. The REYSN patterns of the duckweeds are fractionated relative to both shale and ambient water, with larger distribution coefficients for light compared to heavy REY, probably due to stronger complexation of heavy REY with dissolved ligands. None of the duckweeds displays any anthropogenic GdSN anomaly, regardless of its presence or absence in ambient water.

Our findings show that duckweeds have a strong bioaccumulation potential and are quasi-hyperaccumulators of REY and further corroborate the conservative behaviour of Gd-CAs in the environment.