Rare earth elements in sediments of the Pearl River Estuary, China: distribution, influencing factors, and multi-index assessment

Purpose The main objectives of this study were to investigate the distribution characteristics and evaluate the potential ecological hazard associated with rare earth elements (REEs) within the Pearl River Estuary (PRE) sediment. Furthermore, we still have not fully understood the contamination and potential ecological risks of REEs in aquatic sediments. Moreover, the factors influencing their distribution remain unidentified. Hence, we selected the PRE as the central focus for our case study in this paper. Materials and methods Sediment samples in this study (0–20 cm) were collected from 156 locations. The total organic carbon (TOC) and grain size were measured. The concentrations of REEs were determined by inductively coupled plasma mass spectrometry (ICP-MS). Furthermore, contamination models, including geoaccumulation index ( I geo ), enrichment factor (EF), contamination factor ( C_f^i ), and pollution load index (PLI), along with ecological risk assessment models potential ecological risk factors ( E_r^i ) and ecological risk index ( RI ) have been employed to evaluate pollution levels and ecological risks. Results The concentrations of sum REEs (ΣREEs) were in the range of 51.21 to 567.08 mg kg −1 , with an average of 299.06 mg kg −1 . We identified two accumulation centers for REEs, indicating that these elements primarily originated from these two centers. It can be seen from the values of EF of REEs that these elements showed minimal enrichment. Moreover, the pollution load index (PLI), which assesses the combined contamination of REEs, was computed to evaluate the collective contamination in the study area. The PLI results indicate a slight multi-element contamination in the research region. Furthermore, based on the E_r^i values, it is evident that all studied REEs pose a low ecological risk. Conclusions The distributions of REEs were mainly controlled by TOC and median grain size. The RI was also calculated to assess the combined potential risks on the ecology. The study’s findings indicate that the PRE’s sediments produce low ecological risks.