Abstract

OLU-OWOLABI, Bamidele I.; AGUNBIADE, Foluso O.  and  ADEBOWALE, Kayode O.. Metal speciation in sediments from crude oil prospecting in the coastal area of Ondo State, Nigeria. Earth Sci. Res. J. [online]. 2013, vol.17, n.1, pp.41-51. ISSN 1794-6190.

Information obtainable from metal speciation is far more valuable regarding the bioavailability, toxicity and fate of metals than information from total metal data. Metal speciation on sediment was thus carried out in this study to assess the bioavailability, fate and mobility of As, Cd, Cr, Fe, Mn, Ni, Pb, and V in the crude oil prospecting area of Ondo State in Nigeria. Five operationally-defined metal species were obtained using the sequential extraction method: exchangeable species, carbonate-bound species, iron/manganese-bound species, organic-bound species and residual species. Species' concentration, spread and relative abundance were used to assess their fate, mobility and potential toxicity. The crude oil exploration site and the mouth of the estuary had the highest concentrations of these metals compared to other sites. The exchangeable and the organic-bound high risk species were most predominant in the crude oil exploration sites but their concentration became reduced downstream away from these sites. The residual fraction (the least in the crude oil prospecting site) was the most predominant in the most distant sites downstream. There were indications of self-management of the metals in the coastal system through favourable biogeochemical reactions partitioning metals from high risk species from low risk ones and the non-toxic residual fraction. It could, however, be concluded that sediment from the crude oil prospecting area may serve as non-point sources for metals contaminating the coastal system, they have higher metal bioavailability and higher toxicity risk potential than other sites (which should be curtailed).

Keywords : metal; fate; speciation; biogeochemical reaction; coastal sediment.

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