Assessment of rare earth elements in Asejire Lake, Nigeria

This study evaluated the distribution of rare earth elements (REEs) in the Asejire Reservoir, Southwest Nigeria, a region lacking comprehensive REE assessment despite the growing concern over REE contamination due to industrial and technological expansion. Using inductively coupled plasma-mass spectrometry (ICP-MS), 12 water samples were analyzed to determine REE concentrations. The total REE (∑REE) concentrations ranged from 10.35 to 13.44 μg/L. The anomalies for Cerium (Ce/Ce*), Europium (Eu/Eu*) and Gadolinium (Gd/Gd*) were 0.19–0.24, 0.18–0.24, and 0.94–1.23, respectively. These values indicate strong negative anomalies for Ce/Ce* and Eu/Eu*, while Gd/Gd* exhibited a slight positive anomaly. These results suggest that the water in the study area is relatively pristine with respect to REEs. The enrichment factor (EF) analysis showed slight enrichment/contamination (1 ≤ EF < 2) for light REEs (LREEs) and middle REEs (MREEs), while heavy REEs (HREEs) mostly showed no enrichment (EF < 1). Notably, most samples had Lanthanum (La) and Cerium (Ce) concentrations above the indicative Admissible Concentration (iAC = 2.0 μg/L) for drinking water, implying potential adverse effects from chronic ingestion. Principal component analysis (PCA) revealed that 71.2% of the variability is accounted for by the first two principal components (PC). PC1, which accounts for 61.22%, is attributed to natural inputs of REEs, while PC2, accounting for 10.51%, suggests some anthropogenic input. In conclusion, this study reveals that the Asejire Reservoir is slightly impacted by anthropogenic influences and local authorities should implement appropriate measures to prevent further deterioration.