Assessment of The Water and Sediment Quality of Some Lagoons Within the Greater Accra Region

ABSTRACT

The Ghanaian ecosystem plays host to various lagoons which serve different purposes. The most important of them is being home for different types of fish species. Examples are Sarotherodon melanotheron (Cichlidae) which is popularly called blackchin tilapia and Tilapia guineensis (Bleeker) also known as redchin tilapia. Quality assessment was done to ascertain the level of pollution in water and sediment samples from Sakumo, Chemu and Kpeshie lagoons. Physicochemical parameters (pH, TSS, alkalinity, EC, TDS, Cl– , NO3 – and PO4 3–), heavy metals (Cu, Pb, Fe, Ni, Zn and Mn) and pesticide residues (DDT, DDD, DDE, aldrin, dieldrin, fenitrothion and chlorpyrifos) were analysed in this work. The atomic absorption spectrophotometer used for the determination of heavy metals was VARIAN AA 240FS (Fast Sequential Atomic Absorption Spectrometer) fitted with a deuterium background corrector. Varian CP-3800 Gas Chromatograph with a Combi PAL Autosampler, Electron Capture Detector and Pulse Flame Photometric Detector was used for the analyses of pesticide residues. Sampling was done in the wet and dry seasons. The results obtained were compared with EPA, WHO and USEPA recommended limits.

The results indicated that there were significant differences in concentrations of the physicochemical parameters and heavy metals between the two seasons. Most of the physicochemical parameters and heavy metal concentrations generally recorded mean values above their respective EPA, WHO and USEPA recommended limits. Correlations between metals in the sediment samples were investigated to possibly identify metals that might possess the same sources. Statistically significant and positive correlations were found between Cu and Pb, Cu and Fe, Cu and Ni, Cu and Zn, Cu and Mn, Pb and Fe, Pb and Ni, Pb and Zn, Pb and Mn, Fe and Ni, Fe and Zn, Fe and Mn, Ni and Zn, Ni and Mn, and Mn and Zn. This suggests that, metals in each combination were originating from a particular source. xviii Results were below detection limit for the study of pesticide residues in water and sediment samples in this research. This gives a general indication that the lagoons were unpolluted with respect to pesticide residues studied in this research and thus, there could be a possibility of pollution by other pesticide residues beyond the scope of this study.