Heavy-Metal Fractionation in Surface Sediments of the Cauvery River Estuarine Region, Southeastern Coast of India

Geochemical fractionation of iron (Fe), manganese (Mn), copper (Cu), chromium (Cr), lead (Pb), zinc (Zn), and nickel (Ni) were determined using five-stage sequential extraction in sediments collected from estuarine stretches of Cauvery River delta on the eastern coast of India with emphasis on seasonal variation. Abundance of metals in terms of sum of total fractionations varied in the following order: Fe > Mn > Cr > Zn > Cu > Ni > Pb. Exchangeable fraction, believed to be bioavailable, showed differential abundances during the dry and wet seasons in the following order: Pb > Zn > Cu > Mn > Ni > Cr > Fe and Zn > Cu > Cr > Ni > Mn > Pb > Fe, respectively, indicating the possibility of anthropogenic influence. Among nonlithogenic fraction, organic matter–bound fraction is the second largest and a key scavenger for all of the heavy metals studied except Fe and Mn. A significant portion of Cu-associated organic matter fraction shows strong association of Cu with organic matter at most of the sampling sites. Environmental risk of metals evaluated using risk-assessment code and mobility factor showed low to high risk for Pb, Zn, and Cu. The results of the present study also hint at notable enrichment of heavy metals in the certain pockets of the Cauvery Estuary.