Distribution and source determination of rare earth elements in sediment collected from the continental shelf off Hainan Island, China

Contents of rare earth elements (REEs), major elements, and the total organic carbon (TOC) were determined for 152 surface sediment samples collected from the continental shelf off Hainan Island (CSHI). From high to low, the average contents of REEs were as follows: Ce > La > Nd > Pr > Sm > Gd > Dy > Er > Yb > Eu > Ho > Tb > Tm > Tm. The LREEs in the south are more abundant than in the north, which is shown by the higher LREE/HREE values in south than in the north. This resulted higher values for the LREE/HREE ratio in the south than in the north. The mean enrichment factor (EF) could be arranged from highest to lowest as follows: Tm > Sm > Pr > Er > La > Lu > Ce > Tb > Eu > Nd > Yb > Gd > Ho > Dy. The EF indicates that pollution as a result of human activity was more serious in the southeast of the study area than in the north. The factors affecting the REE concentrations in this area include naturally occurring minerals and industrial pollution. Based on the spatial variation of upper continental crust (UCC)-normalized REE concentrations, the CSHI was classified into three geochemical provinces. The sediment of province I was controlled by the Red and Pearl rivers. The composition of the province II is mainly controlled by the Red River and the Pearl River, although some sediments have originated from the South China Sea Island. Province III sediments mainly originated from sources on Hainan Island.