SPATIO-TEMPORAL VARIATION OF HEAVY METAL CONCENTRATIONS IN WATER, SEDIMENT AND IN SELECTED FISH SPECIES IN SHIRORO LAKE, NIGER STATE, NIGERIA.

Abstract

Anthropogenic activities contribute the most to heavy metals pollution of water bodies around the world. This study was conducted to determine the spatial and temporal variation of heavy metal concentrations in sediment, water and in selected fish muscle from Shiroro Lake Niger State, Nigeria. Sediments and water samples were collected from three different stations across the lake for a period of eight (8) months between February and September 2019. Heavy metals that were analyzed were chromium Cr, cadmium Cd, lead Pb, zinc Zn and copper Cu. Analysis of heavy metals was carried out on the muscles of three commercially important fish species in the lakes, which were Alestes macrolepidotus, Bagrus bayad and Clarias gariepinus. Water quality parameters showed that dissolved oxygen ranged from 2.20 - 4.10 mg/L, temperature, 26.60 - 30.20 oC, biological oxygen demand, 1.20 - 3.00 mg/L, conductivity 49 - 120 µS/cm, alkalinity 18 - 36 mg/L, phosphate 0.16 - 2.28 mg/L, sodium 7.56 - 14.00 mg/L, pH 6.56 - 7.96, total dissolved solids 75 - 99 mg/L, total hardness 30 - 48 mg/L and potassium 1.16 - 2.42 mg/L. Analysis of the concentration of heavy metals of sediment samples collected across the three stations showed that zinc ranged 0.095 - 0.25 mg/l, copper 0.015 - 0.905 mg/L, lead 0.00 - 0.15 mg/L, chromium 0-0.03 mg/L and cadmium 0 - 0.015 mg/L. Analysis of the concentration of heavy metals of water samples collected across the three stations showed that zinc ranged 0.01 - 0.18 mg/L, copper 0.01 - 0.165 mg/L, lead 0 - 0.2 mg/L, chromium 0.00 - 0.01 mg/L and cadmium 0 - 0.01 mg/L. Cadmium exceeded the toxicity threshold in the water sample in line with World Health Organization (WHO) standard in drinking water. The result also showed higher levels of Zn 1.47 ± 0.50 mg/g and Cu 0.73 ± 0.31 in fish in comparison to other heavy metals examined. All the heavy metals in fish samples were below WHO maximum stipulated limit. The results of the mean values of potential ecological risk index (PERI) across all stations showed that Zn 0.083, Cu 0.29, Pb 2.06, Cr 0.03 and Cd 0.48 while the comprehensive PERI value ranged between 0.617-6.902, therefore the PERI value obtained showed that the ecological risk level is slight. The results of the mean values of the Geo-accumulation index reported that Zn -2.42, Cu -2.06, Pb -1.56, Cr - 0.92, and Cr -0.75, therefore the geo-accumulation index values of the five heavy metals analyzed for across all three stations obtained from this study were negative i.e. (<0), this indicates an unpolluted state of the sampling stations. The results of the mean values of the enrichment factor (EF) reported that Zn 0.08, Cu 0.05, Pb 0.41, Cr 0.02, and Cr 0.02. Enrichment factor (EF) values of the five heavy metals analyzed for across all three stations obtained from this study were below one (<1), this indicates crustal enrichment origin of the sampling stations. The result of physicochemical parameters obtained from this research indicates a low level of pollution because all the water quality parameters recorded were either slightly below or within WHO permissible limit. The water in Shiroro Lake is not safe for human consumption as it can lead to Cd exposure.