Seasonal Mean Levels of Heavy Metals in Water and Associated Sediments from Ajawere River in Oke-Osun Farm Settlement, Osogbo, Nigeria

Abstract

The seasonal mean variations of As, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, V and Zn in the water and sediments of Ajawere River in Oke-Osun Farm Settlement, Osogbo, Nigeria were evaluated.  Samples collected were analyzed for their heavy metal levels using Graphite Furnace Atomic Absorption Spectrophotometer (GF-AAS).  Seasonal mean ranges of heavy metals in the river sediments (mg/kg) were 3.39 ± 1.34 Cd to 43.24 ± 6.15 Cr in the rainy season and 4.56 ± 1.21 Ni to 55.35 ± 4.29 As in the dry season.  Seasonal mean levels of heavy metals (mg/L) in the river water ranged between 3.02 ± 0.72 As and 179.49 ± 21.45 Fe in the rainy season while the dry season mean levels ranged from 3.09 ± 1.65 Co to 278.81 ± 51.59 Fe.  Wide seasonal variations were observed for Cr, Cu, Mn, Ni, V and Zn in the sediments and for all the other metals apart from As, Ni and V in the water samples.  The I-geo values obtained indicated that the sediments were moderately polluted with respect to Cr, Cu and Pb, and was either heavily polluted or very heavily polluted with respect to As and Cd. Metal levels in the river water, in many cases, were above the specified guideline limits for natural waters.  The results obtained from this study indicated that the river sediment and water samples from Oke-Osun Farm Settlement were contaminated with heavy metals in varied degrees and gave cause for concern.