Tracing emerging contaminants from the Baltic Sea and North Sea in fjord waters in southern Norway with rare earth elements as far-field tracers

Knowledge of geogenic and anthropogenic rare earth elements and yttrium (REY) in fjords in Norway and elsewhere is still limited despite the importance of fjords for biodiversity and economy and the known ecotoxicity of the REY. We provide complete sets of REY data for fjord waters and a river in southern Norway and for several stations along the coasts of Denmark and Sweden, which characterise Baltic Sea outflow water. Shallow fjord waters show high REY concentrations and shale-normalised (_SN) patterns that resemble those of the river water input. Deeper waters show lower concentrations, seawater-like REY_SN patterns, and the Pr_SN/Tb_SN ratios (≥0.5) typical of fjord waters. Some of the samples show elevated Gd/Tb ratios and distinct positive Gd anomalies, revealing the presence of anthropogenic Gd originating from constrast agents used in magnetic resonance imaging (MRI). We emphasise that all water samples from the Baltic Sea outflow taken over a twelve months period show large positive Gd anomalies, suggesting a permanent flux of anthropogenic Gd from the Baltic Sea into the Skagerrak. Combined with literature data, our results suggest that the anthropogenic Gd in the fjords of southern Norway is not derived from local sources. It rather originates from the Baltic Sea and southern North Sea and is transported northward by currents along the coasts of Sweden, Denmark and Germany. If application of Gd-based contrast agents in MRI continues to increase, this signal will get stronger in the future and be transported even further north. Overall, our data for geogenic REY and anthropogenic Gd in fjord and bay waters from southern Norway and in the Baltic Sea outflow show that local hydrography exerts an important control on the concentration and distribution of trace elements which may be (micro)nutrients and/or (micro)pollutants in fjords. This needs to be considered in environmental impact studies.