Total and Acid-Leachable Trace Metals in Surface Sediment of Sundarban Wetland and Adjacent Hooghly River Estuary

Abstract

The chapter examines a detailed account of the geochemical assessment of ten trace metals (TMs) in total and acid-leachable (ALTM) fractions of the surface sediments (grain size Mn (549.51 ± 121.85) > Zn (87.63 ± 15.86) > Cr (64.83 ± 12.81) > Ni (55.67 ± 8.66) > Cu (49.13 ± 20.24) > Co (41.48 ± 9.03) > As (36.65 ± 11.74) > Pb (24.78 ± 2.64) > Cd (4.63 ± 1.65). An overall similar trend was also discernible for leachable fractions, except two hazardous trace metals, Pb and As. The mean bioavailability for the TMs revealed that Pb was the most mobile (27.10%), followed by Cu, Zn, and As (13–17%) and Cd, Ni, Co, and Cr (4–7%), mainly concerned with multitude of human activities (industrial effluents, discharge of sewage, agricultural runoff, etc.). Maximum concentration of majority of the TMs was evident at the lower stretch of the estuary. The geoaccumulation index (Igeo) and contamination factor (CF) values affirm the intensity of severe pollution by Cd and As. The ecological risk associated with the TMs in sediment was considered to be occasionally observed for As, Cd, Cu, and Ni (effects range low (ERL)–effects range medium (ERM)) and frequently observed for Ni (greater than ERM) based on assessment using consensus-based sediment quality guidelines (SQGs). A similar pattern of correlations was observed for TMs and ALTMs as evident from Pearson correlation matrix, whereas ALTMs exhibited significant association with silt. The study provides a useful tool for sustainable management in this productive estuarine complex.