Critical raw materials in river waters: First observation of lutetium microcontamination of the Isère and Rhône rivers, Southern France

The increasing use of rare earth elements and yttrium (REY) in enabling technologies is accompanied by their increasing release into the environment as emerging (micro-)contaminants. Starting with the detection of anthropogenic gadolinium (Gd) contamination in German rivers in 1996, currently available data on the distribution of REY in surface waters worldwide show anthropogenic positive Gd anomalies derived from Gd-based contrast agents used in magnetic resonance imaging, and at few locations positive La and Sm anomalies. However, in addition to the omnipresent positive Gd anomalies, the Isère River downstream of the city of Grenoble in southern France shows large positive lutetium (Lu) anomalies. These data which are confirmed by different analytical approaches in two different laboratories, are the first report ever of large positive Lu anomalies observed in surface waters. The very large size of the positive Lu anomaly most strongly suggests that this represents an anthropogenic Lu (micro-)contamination of the river. The origin of the anomalously high Lu concentrations can be tracked to the effluents from the wastewater treatment plant (WWTP) Aquapole in the city of Grenoble. This Lu is then diluted and hence decreases in concentration further downstream, but the anthropogenic Lu anomaly is still visible in REY data for the Rhône River. Repeated sampling over 15 months strongly suggests that the Lu (micro-)contamination of the Isère and Rhône rivers from the WWTP Aquapole is persistent and not a transient phenomenon related to a one-time event. The anthropogenic Lu shows natural isotope abundances and does not reflect pollution with radionuclides. The addition of Lu to the set of critical metals present as microcontaminants of the hydrosphere clearly reveals the necessity of better monitoring the distribution of REY and other formerly "exotic" elements and their release into the environment.