Potential ecological risk assessment of rare earth elements in sediments cores from the Oualidia lagoon, Morocco

Abstract

ABSTRACT This study’s objective was to evaluate the depth profiles of rare earth elements (REEs) in two Pb-210 dated sediments cores retrieved from the Oualidia lagoon, reconstruct their anthropogenic history, and assess their potential ecological risk. The sediment cores analysis was carried out using instrumental neutron activation analysis. Other physical-chemical parameters (bulk, organic matter, grain size) were also measured. The results indicated that the highest values were recorded in the topmost layers of the sediment cores and depleted with depth. The historical records of REEs revealed an exponential increase in their concentrations from the 50s. The enrichment factor, geo-accumulation index, and contamination factor calculated for each sediment core layer have exhibited important concentrations of Gd, Sm, and Eu, suggesting an anthropogenic origin of detected elements. Based on ecological risk >40 and the risk index >220, Gd, Eu, and Sm pose a high risk on the study area, while the other elements present moderate and mild risk. The obtained results revealed an increasing tendency of REEs accumulation into the Oualidia lagoon and suggested that a new source is feeding the lagoon sediments by these elements. These findings provided a clear picture of REEs evolution between 1903 and 2014 and baseline information on the historical deposition of these elements in the Oualidia lagoon.