Abstract
BACKGROUND: Heavy metals in water systems are a human health concern as they can enter the food chain. OBJECTIVES: Heavy metal and particle size determinations were used to determine the sediment quality of three fishponds in Osun State, Nigeria and their feeder streams. METHODS: Sediment samples were collected in triplicates from the streams and their associated fishponds and the accumulations of nine heavy metals (lead (Pb), cobalt (Co), cadmium (Cd), chromium (Cr), copper (Cu), nickel (Ni), iron (Fe), manganese (Mg), zinc (Zn)) in the sediment were investigated seasonally. Particle size distribution and textural class of the samples were also determined. RESULTS: Metal concentrations recorded in bottom sediment varied widely and exhibited fluctuations among the different ponds and streams, especially in the values of Fe, Cu, Mn, Cr, Zn and Pb. There was a significant difference (p<0.05) in the concentrations of metals across the three investigated locations. The metals in the sediments occurred in the order of Fe>Cu>Ni>Zn>Pb>Cr>Mn>Co in Ilesha, Fe>Cu>Ni>Zn>Mn>Co>Pb>Cr in Osogbo and Zn>Fe>Ni>Mn>Cu>Co>Cr>Pb in Yakoyo. A closely related order of Fe>Mn>Ni>Zn>Cr>Cu>Se>Pb>Mo>Cd was observed in River Eku. The selected streams and their associated fishponds were fairly polluted, with the Yah fishpond (Ilesha) having the highest heavy metal pollution compared to Arula fishpond (Osogbo) and Ewuru/Rara fishpond (Yakoyo). The concentrations of accumulated heavy metals depended on the textural class of the sediment. CONCLUSION: Pollution has reached levels hazardous to human health compared to standard limits for aquaculture development. Stream and fishpond sediments should be analyzed at regular intervals as a quality assurance process to ensure that there are no toxic substances in the ponds, leading to possible bio-accumulation and magnification. This will help guarantee the health of the aquatic ecosystem, humans and the environment.