ABSTRACT
Forty seven (47) sediment samples from two bore holes from different depths and two river bed sediments from Meghna River were collected from arsenic hot spot area of Bangladesh for geochemical analyses. Concentrations of major elements (SiO2, CaO, MgO, K2O, Na2O, Fe2O3, Al2O3, Mno, TiO2) and trace elements (V, Cr, Co, Ni, Cu, Zn, Rb, Sr,Y, Zr, Nb, Ba, La, Ce, Nd, Th and Pb) of sediment were analyzed by XRF (X-ray Fluorescence Spectrometer). Total As of bulk sediment was measured by ICP-MS. Total As content in sediment ranges from 1.91 mg kg−1 to 7.97 mg kg−1 (average 3.60± 2.04 mg kg−1). Higher content of As (7.97 mg kg−1) is observed in clayey sediment and lower content (1.91 mg kg−1) is found in sandy sediments. The river bed sediment contains arsenic ranges from 1.65 mg kg−1 to 2.27 mg kg−1. The sequential extraction of arsenic along with the strong positive correlation between As, Fe and Mn suggest that As is adsorbed by FeOOH/MnOOH and liberated from sediment into groundwater due to reductive dissolution of FeOOH and MnOOH. The bulk mineralogy of the sediments was determined by X-ray powder diffraction (XRD) method, which shows that quartz, feldspar, mica and chlorite are dominant mineral in sediment of the study area. The positive correlation between As and intensity of mica and chlorite mineral also reveals that the possible source of As in sediment are mica and clay minerals.
