Rare earth elements in alkaline Lake Neusiedl, Austria, and the use of gadolinium microcontamination as water source tracer

Abstract

The rare earth elements are increasingly used in high-tech enabling technologies and have become emerging (micro)contaminants. Their environmental impact is poorly known and regulated. Here we focus on the rare earths and yttrium (REY) systematics in Lake Neusiedl at the border between Austria and Hungary. Lake Neusiedl is the largest alkaline steppe lake in Europe and is characterised by unique and dynamic geobiological conditions. Steppe lakes, in general, are very susceptible to anthropogenic influence, as contaminants can easily accumulate under an endorheic setting. We report the first REY data for water samples from Lake Neusiedl and surrounding lakes. Lake Neusiedl shows the REY signature typical of alkaline lakes, i.e. a positive Ce anomaly and enrichment of heavy relative to light REY. More importantly, we identified prominent anthropogenic positive Gd anomalies that can be used as a water source tracer in Lake Neusiedl. The anthropogenic Gd can be tracked back to the Wulka River, one of its tributaries, and originates from medical contrast agents. As these cannot be removed from sewage during wastewater treatment, they are released into the river with the effluents from wastewater treatment plants. Additional REY data from the surrounding smaller lakes suggest that smaller amounts of anthropogenic Gd may also be present in local groundwater. We demonstrate that the anthropogenic Gd can be utilised to quantify the riverine component in Lake Neusiedl waters. However, as it reveals the presence of wastewater-derived substances in the National Park waters in general, it also hints to the potential presence of other contaminants that may have higher (eco)toxicities than the contrast agents.