The use of gadolinium and europium concentrations as contaminant tracers in the Nida River watershed in south-central Poland

This paper presents the results of rare earth element (REE) determinations in the Nowiny wastewater treatment plant (NWWTP) effluents and Nida River system waters of the southeastern Kielce Region (south-central Poland). Of the REE examined, gadolinium and europium turned out to be very useful for pinpointing anthropogenic and geogenic sources. Anthropogenic gadolinium (Gdanth), used as a contrasting agent in magnetic resonance imaging (MRI), is released from the NWWTP into the river drainage system. This micropollutant is traced downstream over the distance of about 15 km. This river stretch is characterized by a strong positive NASC-normalized Gdanth anomaly with the GdNASC/GdNASC* ratio above 1.1 (1.80–15.57) and the Gdanth input varying from 44 to 94%. Two additional positive Gdanth anomalies recorded in the rivers Bobrza and Nida point out to mixing of effluents derived from the NWWTP and other local wastewater treatment plants. In contrast, the Gdanth-uncontaminated waters upstream, or downstream far away from the NWWTP display a distinct positive NASC-normalized Eu anomaly highlighted by a high Eu/Eu* ratio in the range of 2.87 to 29.70. The lack of Gdanth anomaly upstream from the NWWTP also indicates that there is no leakage of municipal sewage from the sanitary collector sewer into the Silnica River. Thus Gd as a contaminant may be effectively used as a tracer in similar pollution studies because it is relatively simple and cost-effective to discriminate between contaminant concentrations and normal background concentrations.