Application of sequential leaching, risk indices and multivariate statistics to evaluate heavy metal contamination of estuarine sediments: Dhamara Estuary, East Coast of India Subas Chandra Asa & Prasanta Rath & Unmesh Chandra Panda & Pankaj Kumar Parhi & Satyanarayan Bramha Received: 24 January 2012 / Accepted: 2 January 2013 / Published online: 29 January 2013 # Springer Science+Business Media Dordrecht 2013 Abstract In the present study, concentration of some selected trace metals (Fe, Mn, Ni, Co, Pb, Zn, Cu, Cr and Cd) are measured in Brahmani, Baitarani river complex along with Dhamara estuary and its near shore. Chemical partitioning has been made to establish association of metals into different geochemical phases. The exchangeable fraction is having high environmental risk among non-lithogeneous phases due to greater potential for mobility into pore water. The metals with highest bio-availability being Cd, Zn and Cr. The metals like Mn, Zn, Cd and Cu represent an appreciable portion in carbonate phase. Fe–Mn oxides act as efficient scavenger for most of the metals playing a prime role in controlling their fate and transport. Among non-lithogeneous phases apart from reducible, Cr showed a significant en- richment in organic phase. Risk assessment code values indicate that all metals except Fe fall under medium-risk zone. In estuarine zone Cd, Zn, Pb and Cr are released to 32.43, 26.10, 21.81 and 20 %, respec- tively, indicating their significant bio-availability pose high ecological risk. A quantitative approach has been made through the use of different risk indices like enrichment factor, geo-accumulation index and pollution load index. Factor analysis indicates that in riverine zone, Fe–Mn oxides/hydroxides seem to play an important role in scavenging metals, in estuarine zone, organic precipitation and adsorption to the fine silt and clay particles while in coastal zone, co-precipitation with Fe could be the mechanism for the same. Canonical discriminant function indicates that it is highly successful in discriminating the groups as predicted. Keywords Heavy metals . Sediment . Sequential extraction . Ecological risk assessment . Factor and discriminate analysis Environ Monit Assess (2013) 185:6719–6737 DOI 10.1007/s10661-013-3060-3 S. C. Asa Department of Chemistry, M.S. College, Baramba, Cuttack, Orissa, India P. Rath (*) School of Applied Sciences, Department of Chemistry, KIIT University, Bhubaneswar, Orissa, India e-mail: pr_kiit@yahoo.co.in U. C. Panda Environment Division, GEOMIN Consultants Pvt. Ltd., Bhubaneswar, Orissa, India P. K. Parhi Minerals Resources Research Division, Korea Institute of Geoscience and Mineral Resources, Daejeon, South Korea S. Bramha Environmental and Safety Division, Indira Gandhi Centre for Atomic Research (IGCAR), Department of Atomic Energy, Government of India, Kalpakkam 603 102 Tamil Nadu, India