Assessment of Rare Earth elements in Asejire Lake, Nigeria

Abstract

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 advancements. Using inductively coupled plasma-mass spectrometry (ICP-MS), we analyzed 12 water samples to determine their REE concentrations. The total REE (∑REE) concentrations ranged from 10.35 to 13.44 µg/L. Cerium (Ce/Ce*), Europium (Eu/Eu*) and Gadolinium (Gd/Gd*) anomalies were 0.19–0.24, 0.18–0.24 and 0.94–1.23, respectively, indicating strong negative anomalies for Ce/Ce* and Eu/Eu*, while Gd/Gd* showed 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 drinking water concentration (iAC = 2.0 µg/L), implying potential adverse effects from ingestion. Principal component analysis (PCA) revealed that 71.2% of the variability is accounted for by the first two principal components (PC): PC1 (61.22%) is attributed to natural inputs of REEs, while PC2 (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.