Rare earth elements (REEs) have garnered increasing attention as emerging micropollutants in aquatic environments. Nevertheless, our knowledge of the pollution, environmental consequences, and hazards resulting from the presence of REEs in aquatic sediments is limited. This research aims to quantify and explain the distribution patterns, identify the sources, determine the pollution levels, and assess the potential environmental and health risks of rare earth elements in the sediments of the Maroon-Jarahi sub-basin (ending in the Persian Gulf). Surface sediment sampling was conducted at 70 stations at the outlet points of the subbasins. Quantitative analysis of the REEs was performed using inductively coupled plasma mass spectrometry (ICP-MS). To evaluate the pollution levels and potential impacts, the geo-accumulation index (I-geo) and enrichment factor (EF) were used, along with ecological and health risk assessment models. The results showed that the concentration of ΣREEs in the surface sediments of the Maroon-Jarahi sub-basin varies from 100.79 to 231.81 mg/kg, and for sub-basins, the Jarahi River in the downstream area also had the highest concentration of LREE, MREE, and HREE. Based on the I-geo index, pollution by Nd, Sm, and Gd was assessed as moderate, whereas the other elements showed no pollution. The analysis of the EF factor also indicated the enrichment of LREEs relative to HREEs, with the highest enrichment observed for the elements Nd, Sm, and Gd. The ecological risk assessment of REEs indicated low ecological risk, with variable values ranging from 21.23 to 112.27, That the largest contribution to the potential ecological risk was related to Lu (17%), followed by Eu (12%), and Gd=Tb=Tm (9%). The analysis of noncarcinogenic health effects based on HQ values also indicated that REEs in the surface sediments of the area have negligible adverse effects on human health. The carcinogenic health risk assessment also showed that the average ILCRs for adults and children are 9.91×10−16 and 6.89×10−15, respectively. The findings of this research indicate the impact of anthropogenic activities on pollution levels and ecological risk associated with some REEs in the sediments of the Maroon-Jarahi subbasin. Therefore, continuous monitoring and the implementation of targeted management measures to control the release of REEs are essential to protect ecological integrity and reduce the potential risks resulting from their accumulation for the health of local communities.
