Rare earth elements and yttrium in Polish rivers and the input of anthropogenic gadolinium into the Baltic Sea

Due to their use in enabling technologies, rare earth elements and yttrium (REY) have become environmental contaminants, and anthropogenic Gd from Gd-based contrast agents (GBCAs) used in medical diagnostics has become a worldwide concern. Contamination of coastal seawater with GBCAs has previously been documented for the North Sea and the outflow of the Baltic Sea. However, the source(s) of this anthropogenic Gd in the Baltic Sea are not yet known. Hence, we investigated the REY distribution in the Polish rivers Oder and Vistula (and some of their tributaries), which are by discharge the sixth and second largest rivers that enter the Baltic Sea. Large positive Gd anomalies (Gd_SN/Gd∗_SN: 4.92 to 44.6) in all rivers studied reveal the presence of anthropogenic Gd which makes up >90 % of the total Gd inventory of these rivers. Ultrafiltration shows that this Gd is truly dissolved and not associated with nanoparticles and colloids. Hence, its physical speciation is in marked contrast to that of the highly particle-reactive geogenic REY. As this anthropogenic Gd is released from wastewater treatment plants, its presence strongly suggests a high probability of contamination with other waste water-derived substances such as pharmaceuticals, endocrine disruptors and hormones. If artificial groundwater recharge with such surface water would be applied to counterbalance reduced rainfall due to climate change, this would have detrimental effects on drinking water quality. As GBCAs are not removed during estuarine mixing, the Oder and Vistula rivers transport significant amounts of anthropogenic Gd into the Baltic Sea. A rough estimate of the annual flux suggests that these rivers alone account for the input of about 1 ton of anthropogenic Gd per year. Our findings strongly underline the need for continuous monitoring to protect human health and ecological integrity in the Baltic Sea.