Rare Earth Elements and Geochemical Partitioning of Zn and Pb in Sediments of an Urban River

Problem statement: Urban river sediment pollution due to Zn and Pb is a serious problem in all over the world. The source and level of Zn and Pb pollution in sediments of Nomi River of Ota Ward, one of the most industrialized areas in Tokyo, Japan is still lacking. Approach: The present study focused on Rare Earth Elements (REEs) and geochemical partitioning of Zn and Pb in sediments of 19 sampling sites of Nomi River in order to examine the mobility pattern. The amounts of Zn and Pb in the liquid extract of 5 (five) geochemical phases were measured by using Inductively Coupled Plasma Mass Spectrometry (ICP-MS) and the concentrations of REEs in sediments were determined by using X-ray Fluorescence Spectroscopy (XRF). Results: Speciation data indicate dominant labile fraction of Zn, which is related to the presence of several anthropogenic influence of the investigated area. Enrichment Factor (EFc) and Index of geoaccumulation (I_geo) value were compatible with the result, which confirm pollution status of Zn. Environmental risk of Zn and Pb were also evaluated using the Risk Assessment Code (RAC) and sequential extraction results and found Zn poses high to very high risk (34-59), whereas Pb poses low to medium environmental risk (0-19). Conclusion: The mean values of REEs and other minor elements were lower or very close to average shale and Japanese river sediment value but Sr, Sn, Zr and Sb contents were little bit higher than average Japanese river sediment values. Anthropogenic activities, prevalent in the study area play a key role in the accumulation of Zn and Pb in aquatic system. Early warning on the sediment pollution to respective authorities help in preserving the aquatic system from further degradation of the river.