Assessment of Water Quality of the Upper Athi River

Organochlorine pesticides have been used extensively in Kenya for pest control. However, due to their toxic nature a large number of OCPs like DDT, Lindane and Endosulfan have been banned in Kenya. Following the ban, a dumpsite was created in Athi River for the pesticides. This site is near one of the tributaries of the Athi River. Leaching of the OCPs could result in the contamination of the river which is used by the communities around it for activities such as washing clothes and cars, farming, swimming and feeding cattle.

The main purpose of this study is to determine the water quality of the river. The specific objectives were; to determine the physico-chemical parameters such as pH, total dissolved solids, Total Suspended Solids, and chemical oxygen demand; determine the microbial contamination; and to assess organochlorine contamination.

Sampling was done during the dry season. Water from three points along the rivers’ course was collected. One point was upstream before the pesticides dumpsite while the other two were after the dumpsite, specifically at the old Mombasa Road Bridge and at the Kitengela Bridge. The UNEP POP Training Manual 2010 was followed for extraction of the OCPs from water. Liquid-liquid extraction with Dichloromethane as the organic phase was performed t0 extract OCPs. The extracts after adequate preparation, were analysed using Gas Chromatography/Mass Spectroscopy.

The microbial contamination at Mombasa Road Bridge was the highest. The amount of Escherichia coli bacteria was 60cfu/mL while that of other coliforms was 420cfu/mL. This indicated presence of high amount of faecal matter relative to the other three points sampled.

Hexachlorocyclohexane was found in the water. Two isomers of this compound; α-HCH and γ-HCH (Lindane) were detected in some of the three sites sampled. The site with the highest concentration of γ-HCH was Kitengela Bridge which had a concentration of 0.451487ppm. Lindane is classified as a moderately toxic pesticide by the World Health Organization. α-HCH was only detected at the upstream sampling point at an average concentration of 0.199359ppm.

The presence of Lindane in the upper Athi River may be as a result of the presence of the dumpsite. Further studies must be conducted in the dry and wet seasons, with more sampling sites in order to get a wider range of information on the contamination of the water and seasonal variation. Also, water further upstream should be analysed for OCPs in order to determine if the OCPs detected in this study were washed away from other parts of the rivers’ course or were indeed as a result of the presence of the dumpsite.

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