Analysis of Trace Metals and Biological Micro- Contaminants in Fish Occurring In Wastewater Treatment Ponds, Kisumu Urban Centre, Kenya

Abstract

Kisumu Municipal Council domestic and urban activities generate wastewater which is collected as effluent and which undergoes stabilization treatment at Nyamasaria wastewater treatment lagoons before being discharged into the main lake. Before discharge the effluent undergoes natural treatment through a series of nine ponds. Some lower ponds support fishery activities. It is probable that the system contains some impurities and pollutants which end up in the fish that grow within. This research sought to assess the levels of heavy metals: Manganese (Mn), Zinc (Zn), Arsenic (As), Lead (Pb), Mercury (Hg) and bacterial contamination in wastewater and fish grown within these wastewater treatment facilities, and to determine the health risk on people who consume such these fish. Sampling was done on a biweekly basis in these wastewater ponds and lagoons. In situ measurements were done for physico-chemical parameters (pH, temperature, dissolved oxygen, turbidity, conductivity). Alkalinity was obtained by titration and reflux method for BOD5 and COD. Laboratory analysis was also done for fish tissue contamination, BOD5, COD, alkalinity and nutrients (nitrates and phosphates). Spread plate and membrane filter technique approach was used in analyzing the coliforms. Standard methods was used to analyze the nutrient levels. Descriptive and inferential statistics were used to summarize the data. Excel statistical package was used in carrying out data analysis in addition to frequency tables and polygons, bar charts and histograms for presentation. One way ANOVA was used to analyze variations within similar data and a two way on different data sets. Stepwise statistical software was used also to consider effect of one data set on the other. Mean temperature was 25.9 0.4 oC, Ph at 7.3±0.2, Conductivity was 717.7±52.2 μScm-1 and Dissolved Oxygen was 2.43±0.4 mgl-l . Alkalinity and turbidity values were 219.1±12.7 mgl-1 and 338.03±53 NTU respectively. Mean values for nitrates and phosphates were 128±41.2 Nμg/l and 1373.52±211.82 Pμg/l, while BOD5 and COD values were 15,515 mgO2/l and 53,917 mgO2/l, respectively. Considering permissible standards set by NEMA and WHO these measured values were higher. The mean values for heavy metals for liver, muscle and fin tissue was 35.1±7.8 mgkg-1 , 28.5±7.5 mgkg-1 and 46.8±18.5 mgkg-1 respectively. Mean value concentrations of Hg and As metals reduced along the tissues of Oreochromis niloticus, Clarias gariepinus and Protopterus aethiopicus. For the effluent contamination levels to be at recommended level before entering the ecosystem, the Municipal Council ought to re-introduce the facultative mechanism which existed thereon and do away with water plants that cover on some sections of the pond system.