Chemical speciation and bio-availability of selected trace metals in the mudflat core sediments of the tropical estuaries, India

Abstract

Mudflat core sediments collected from the middle region of Mandovi and Sharavathi estuaries, India, were analysed for grain size, organic carbon and bulk metals. Further, speciation of Fe, Mn, Ni, Co and Cr was carried out to understand mobilization, bio-availability and their toxicity, and risk to biota was assessed using sediment quality values (SQV) and risk assessment code (RAC). The analysis showed deposition of relatively high finer sediments and organic carbon in the Mandovi estuary, which facilitated adsorption of Fe, Mn, Co and Cr in the bulk sediments. Speciation analysis revealed mobilization of Mn and Co in Fe–Mn oxide and/or organic phases in the studied estuaries. The high concentration of Mn and Co in one or more bio-available phases towards the surface suggested their bio-availability in both the estuaries. SQV revealed concern from Mn, while the RAC indicated medium degree of risk from Mn and Co to the biota in the studied estuaries.