Assessing rare-earth elements and anthropogenic gadolinium in water samples from an urban artificial lake and its tributaries in the Brazilian Federal District

Abstract

This work highlights the rare earth elements (REE) dynamic in water samples from Paranoá Lake and its tributaries in the Brazilian Federal District. Variation of anthropogenic Gd in Paranoá Lake after a 4 years laps time, characterization of regional REE background levels and possible contaminations in the tributaries were studied. REE were assessed by thulium (Tm)-spiked solid-phase extraction followed by ICP-MS. Method validation was performed using synthetic samples and the SLRS-6 reference material. The method was efficient to remove the interfering Ba (>99.99%) with REE recoveries (SLRS-6) varying from 81 ± 6 (Tb) to 105 ± 4% (Dy). In the Paranoá Lake, water samples were enriched for high and middle REE (PrSN/YbSN varied from 0.15 to 0.39, DySN/PrSN ranged from 1.10 to 2.25, DySN/YbSN varied from 0.27 to 0.45) while the tributaries at Southern part of lake presented an enrichment of lower REE (PrSN/YbSN 1.24 and 2.30; DySN/PrSN 0.80 and 0.49). Gd anomalies were observed in the Paranoá Lake samples, with high levels of anthropogenic Gd (Gdanth) nearby two wastewater treatment plants (33.6 and 22.1 ng L−1). No significant increase in total anthropogenic Gd stock was observed compared to 2013 data. Positive Ce anomaly observed in the dissolved phase may be associated to mineral colloids (Fe or Mn oxy-hydroxides) or agricultural supplies, while positive La anomaly registered in waters requires further studies.