Distribution of heavy metals in sediments of Igbede, Ojo and Ojora rivers of Lagos, Nigeria

The distribution of some heavy metals, namely Cd, Pb, Zn, Fe, Cu, Cr and Mn in epipellic sediments of Igbede, Ojo and Ojora rivers of Lagos was studied weekly in the early summer (November) of 2003. The levels of selected trace metals were determined using Atomic Absorption Spectrophotometer (UNICAM 969 AAS SOLAR). Trends in heavy metal burdens in the sediments revealed weekly variations in all the rivers assessed. Statistical analyses also showed different mean levels of trace metals in the aquatic environments, the distribution of which followed the sequence Fe > Zn > Mn > Pb > Cu > Cr > Cd, Fe > Zn > Cu > Mn > Pb > Cr > Cd and Fe > Zn > Mn > Cu > Cr > Pb > Cd in Igbede, Ojo and Ojora rivers respectively. Fe recorded the highest concentration levels (1,582.95 ± 96.57 μg/g–1,910.34 ± 723.19 μg/g) in all the sediments investigated while the Cd levels (0.06 ± 0.10 μg/g–0.47 ± 0.36 μg/g) were the lowest. Expectedly, trace metal concentrations in fine grain muddy sediments of the Igbede and Ojo coastline were much higher than those of Ojora which consist of coarse and sandy deposits covering the near shore area. Generally, the results obtained fell within tolerJ. A. Adekoya ( ) . A. B. Williams Department of Natural Sciences, Covenant University, P. M. B. 1023, Ota, Ogun State, Nigeria e-mail: [email protected] O. O. Ayejuyo Department of Chemistry, Lagos State University, Ojo, Lagos, Nigeria able limits stipulated by World Health Organization (WHO).