Physico-chemical and bacteriological quality of water from five rural catchment areas of Lake Victoria basin in Kenya
Ouma, Seth Otieno
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Dumping of urban, industrial and agricultural wastewater has impacted negatively on the water quality of Lake Victoria. A number of studies have documented pollution in the Lake but several gaps have been identified. Firstly, the focus has been on urban catchment areas and so information on rural areas is missing. Additionally, information on the effects of seasonal variation is limited. Also that individual studies are focused on either the physical, chemical or microbial quality but not all. Lastly, the data is five years or old, so information on the current status of pollution is required. The aim of this study was to determine the effects of seasonal variation on the physical, chemical and microbial quality of water from five rural catchment areas of Lake Victoria. A total of 180 samples were collected during the dry and wet seasons. Colour, pH, temperature, electrical conductivity (EC), dissolved oxygen (DO), turbidity and chloride were determined using portable meters. Total dissolved solids (TDS) and total suspended solids (TSS) were determined by gravimetry. Zinc, aluminium, iron, mercury and lead were analyzed using flame atomic absorption spectrophotometer. BOD, nitrates, phosphate, ammonia and bacteriological analysis were enumerated using standard assays. Colour, chloride, TSS, TDS, zinc, mercury and nitrates were all below the maximum permissible limit. While the following parameters were above the maximum permissible limit: EC (420-753 μS/cm), turbidity (279-554 NTU), BOD (170-330 mg/L), phosphate (0.18-1.22 mg/L) and lead (0.08-0.90 mg/L); temperature (26-27 oC) in dry season; pH (8.9) in Dunga in wet season; aluminium in dry season (0.32-0.62) and in Dunga (0.46 mg/L) and Usoma (0.34 mg/L) in wet season; ammonia in dry season (0.54-0.72 mg/L) and at Luanda Rombo in wet season (0.70 mg/L). Apart from Luanda Rombo (5.3 mg/L) and Usoma (5.5 mg/L) the DO values (3.1-4.7 mg/L) were below the minimum permissible limit. Coliforms ranged between 10-18 MPN/100 ml. Pathogenic bacteria isolated were Escherichea coli (69.6%), Salmonella spp (18.5%), Shigella spp (6.5%) and Vibrio cholerae (5.4%). This study shows that most parameters were above permissible limits and pollutants levels were higher than in previous studies, suggesting a continuation with contamination. Water was more polluted in catchment areas closer to urban areas. Seasonal variations showed that pH, colour, turbidity, TSS, BOD, phosphate, nitrates and coliforms were significantly high (p < 0.001) in the wet season. In the dry season temperature, EC, TDS, heavy metals, chloride and ammonia were significantly high (p < 0.001). High level of pollutants in wet season is due to storm water run offs carrying a higher load of contaminants while in dry season it is likely due to the increased solubility of ions as a consequence of the elevated water temperature and low pH. Dunga is the most polluted and this is because of proximity to largest city, Kisumu with the largest number of activities known to generate a high load of pollutants. High loads of contaminants in water could pose immediate and long term public health concerns to unsuspecting water users especially due to the pathogenic coliforms and heavy metals. Immediate health concerns include cholera, salmonellosis and shigellosis. Therefore, proper policies regarding protection of the Lake Victoria environmental integrity are required and stiff measures should be taken to discourage law breakers.