Textural and geochemical characteristics of off shore sediment of North Bay of Bengal: A statistical approach for marine metal pollution

Abstract

Metal pollution study on sediments of North Bay of Bengal sediments presented in this paper is based on existing Lithostratigraphy of upstream, mineralogy and geochemical analysis of 42 sediment samples. The statistical analysis identifies the metal pollution as well as its apparent source in the off shore regions. Samples were analyzed for grain size, organic content and heavy metals (Fe, Mn, Cr, Cu, Ni, Pb, Cd, Zn and Co) using the sequential extraction method to evaluate geochemical processes and pollution load. In an effort to surmise anthropogenic input, several approaches including classification by quantitative indexes such as enrichment factor, contamination factor, degree of pollution, pollution load index and geo accumulation index, were attempted. Metal speciation results indicate high % of Cd in exchangeable fraction of Mahanadi transect sediments where as a considerable amount of oxidizable fraction of Cr was detected at Dhamra. Quantitative indexes place North Bay of Bengal under moderately polluted zone due to high level of Cd. Normalization of metals to Fe indicated relatively high enrichment factors for Cd and Cr. Factor analysis identified seven possible types of geochemical associations where sediment pH plays a major role for the heavy metal mobility. The higher Cd concentration in exchangeable fraction as well as the higher EF for Cd and Cr present in sediment may pose a risk of secondary water pollution under slightest disturbance in the geo-chemistry of sediments. Comparison study with available data of near costal zones and upstream stratigraphy revealed that open cast mining, overburden dumping, mineral based industrial effluents were the major source of pollution for catchment area contamination. Bay of Bengal is likely to face a serious threat of metal pollution with the present deposition rates unless rigorous pollution control norms are applied. (C) 2015 International Research and Training Centre on Erosion and Sedimentation/the World Association for Sedimentation and Erosion Research. Published by Elsevier B.V. All rights reserved.