Heavy Metals Concentrations in the Sediments of Lagos Lagoon Using Different Geochemical Phases

A. O Adedeji and A. O. Falana
The Polytechnic Ibadan, Ibadan, Nigeria

The determination of heavy metals such as Nickel (Ni), Zinc (Zn), Cobalt (Co), Iron (Fe), Lead (Pb), Cadmium (Cd), Manganese (Mn), Copper (Cu), Chromium (Cr) in association with the sediments of Lagos lagoon was undertaken. Also, the sources of these heavy metals were suggested respectively. This involved assessing the potential negative impacts likely to result from the concentration of these metals and evaluating various environmental conditions in the lagoon. Six samples (6) were chosen for sediments analysis (geochemical) out of 29. In the course of the experiment; these heavy metals were extracted from the sediments in five different geochemical phases using different reagents. The reagents used include: Magnesium Chloride hexa-hydrate, Sodium acetate, Nitric acid, hydrogen peroxide, ammonium acetate, hydroxylamine and hydrofluoric/perchloric acids. All reagents used in the study were of analytical grade. The "selective" extractions were conducted in centrifuge tubes; the leachates were kept and labeled while the residue was used for subsequent fractionation (partitioning of heavy metals). The concentrations of the heavy metals were determined using the Atomic Absorption Spectrophotometer (AAS). The experimental results obtained show that Manganese (Mn) has highest concentration relative in the 1st phase (Exchangeable) while Iron (Fe) has the highest in the 3rd, 4th and 5th phases (Reducible, Bound to Organic Matter and residual). Results are shown in percentages, by trending and correlations. High accumulation of Manganese in the bottom sediments is attributable to the release by various processes of remobilization of industrial wastes. This heavy metal is frequently associated with iron deposits showing a reducing environment. The use of sequential extractions although time consuming furnishes detail information about the origin, mode of occurrence, biological and physiochemical availability, mobilization and transport of trace metals in stream sediments of Lagos Lagoon.