DEPTH-WISE PROFILING OF HEAVY METAL SPECIATION IN THE SEDIMENTS OF SUNDERBAN WETLAND-A PILOT STUDY

Abstract

Core sediment samples from three sampling sites of Sunderban Wetland region, e.g., Lot 8 Jharkhali S2 and Ghusighata S3 are studied by SEM-EDAX, EPMA for major composition and point analysis of selected mineral grain. Total metal analysis of heavy metals like Cr, Mn, Co, Ni, Cu, Zn, Cd and Pb are measured by AAS method. The variations in the concentration of these heavy metals are observed along the depth of the sediment core suggesting changes in their input due to natural and anthropogenic activities. Metal speciation has been done using sequential extraction method. Most of the heavy metals are found to be immobilized in silicate matrix and to some extent as oxides. In addition, these heavy metals are found in other forms e.g., ion-exchangeable and carbonates. The pilot study to evaluate the feasibility of using sequential extraction method to isolate the heavy metals into various chemical forms has been successfully accomplished. Other imaging techniques like SEM-EDAX and EPMA are found to be excellent supplementary methods to obtain useful data like shape, morphology and texture of the sediments, major composition (in this study it has been primarily silicate matrix) etc. In addition, EPMA is also found to be a good method for estimating minor elements, e.g., Mg, Ca, Ti, Mn.