Understanding of Chemical Speciation of Lead, Zinc and Copper in Vertical Profile of the Sediments of the Brahmaputra River, Assam, India

Lead (Pb), zinc (Zn) and copper (Cu) are ubiquitous in the environment as a result of anthropogenic and geogenic processes. The fate of these metals in the environment is largely governed by their speciation, which is influenced by sediment properties. Therefore present study focusses on the distribution of Pb, Zn and Cu in different chemical forms in core sediments. Four sediment cores were collected from upstream to downstream of the Brahmaputra river. Metal speciation study revealed that most of the heavy metals were associated with the residual fraction. Among non-residual fraction Zn and Pb were mainly associated with reducible fraction while Cu was associated with oxidisable fraction. The bioavailable fractions for Pb are found to be comparatively higher. Correlation analysis was carried out among different geochemical fractions of heavy metals and sediment properties. It was found that most of the non-residual fraction of heavy metals is significantly correlated with grain size, pH and organic matter. Significant correlation was found between metals (Pb, Cu and Zn) in oxidisable fraction and organic matter. The risk assessment code suggests low to medium risk for all heavy metals.