IOSR Journal of Applied Chemistry (IOSR-JAC) e-ISSN: 2278-5736.Volume 7, Issue 8 Ver. I. (Aug. 2014), PP 21-28 www.iosrjournals.org www.iosrjournals.org 21 | Page Chemical Speciation and Mobility of Heavy Metals in the Sediments of Selected Streams in Ibadan Metropolis, Nigeria I. A. Ladigbolu Department of Physical & Chemical Oceanography Nigerian Institute for Oceanography & Marine Research, Victoria Island, Lagos Abstract: Speciation of the following heavy metals, Cadmium (Cd), Chromium (Cr), Cobalt (Co), Copper (Cu), Lead (Pb), Nickel (Ni) and Zinc (Zn) were studied in the sediments of five streams in Ibadan metropolis namely Odo – ona (S-1), Ogunpa (S-2), Ogbere (S-3), Kudeti (S-4) and Gege (S-5). Highest percentage (%) of Cr, Co and Ni were observed in the residual fraction, followed by Cu and Cd in the oxidisable fraction and Zn and Pb in the reducible fraction. Exchangeable fraction contributed the least % of all the metals studied except in the (S-1) where the % metals contribution of exchangeable fraction was more than that of carbonate bound fraction. The presence of more than 50% of Pb, Cd, Cu, Zn in non – lithogenous phase of all the studied streams, Co in (S-1) and Ni in (S-2) indicates the influence of anthropogenic activities. Their readily availability for plants and aquatic biota uptakes also suggested greater environmental risks. Cr, Co and Ni in all the studied streams of Ibadan metropolis were influenced by rock and soils formation (weathering) except Co and Ni in S-1 and S-2 streams respectively. However, their unavailability for uptakes indicated no environmental risks under natural conditions. Keywords: Speciation, heavy metals, environmental risks, lithogenous, sediments I. Introduction Chemical speciation of metals in the sediments is the identification and quantification of different forms and process in which metals can occur in the sediments (Xian X, 1989). It can also be referred to as the study of chemical minerals in the sediment samples through which metals in the sediment are usually separated into different geological phases with varying mobility, leachability and bioavailability. The geological phases in which metals exist in the sediment can be classified into two major groups, lithogenous / residual fraction and non-lithogenous fraction. Lithogenous or residual fraction metals are not available in long term for bio – uptake, due to strong bond which exists between these metals and crystal lattice of silicate of the sediments and soils. Therefore, they are from natural source that is rock or soils weathering while non- lithognous fractions metals are readily available in short term (Badri and Anston, 1983). Non-lithogenous (mobile) fraction can be further subdivided into exchangeable fraction, carbonate bound fraction, reducible (Fe-Mn oxides / hydroxides) fraction and oxidisable (organic matter / sulphide) fraction (O’Neill et al; 1981).Metals associated with the four fractions that make up the non – lithogenous fraction most of time comes from anthropogenic sources and they are more available for uptakes and bioaccumulation in aquatic biota, although their availability is many a time pH, redox- potential and temperature dependent (Gambrell, 1994, and Schlinder, 1991). Furthermore, effective characterization of the behaviour of heavy metals in the sediment require both the knowledge of total heavy metals concentration and chemical speciation (Zauyah et. al; 2004), because information obtained from them would give an insight into the environmental impact of these metals and reliably predicts their sources {i.e. anthropogenic and natural (rock or soil weathering)}, mobility, bioavailability, distribution and toxicity in the environment. The orientation of this study is to study the speciation of the following heavy metals; Zn, Cu, Cd, Ni, Pb, Cr and Co in the sediments of the following five (5) important multipurpose streams / Rivers of Ibadan metropolis; Odo-ona (S-1), Ogunpa (S-2), Ogbere (S-3), Kudeti (S-4) and Gege (S-5) to establish the quantity and distribution patterns of the severally reported heavy metals in the sediment of each of the above mentioned streams for proper understanding of their biogeochemical processes, bioavailability and their tendency to cause health hazard. II. Materials and Methods Study Area The study areas are Ogunpa, Gege, Odo-ona, Ogbere and Kudeti streams in Ibadan metropolis. Ibadan metropolis is located at latitude 7°21’N and longitude 3°53’E, about 110km northeast of Lagos, Nigeria. The study area is characterized by tropical humid climate with two distinct seasons: the wet season which occurs between March and October with an average annual rainfall of about 1,250mm and dry season from November