Determination of Possible Sources and Seasonal Fluctuation of Organochlorine Pesticides in Lake Nakuru

Abstract

This thesis reports on the determination of organochlorine pesticides sources in lake Nakuru. The samples investigated were collected from Lake Nakuru and rivers within the Lake's catchment area, viz Rivers Njoro, Nderit, Makalia and Larmudiac. Water and sediment samples were collected using a macvuti and an ekman sampler respectively, and these were collected both from the lake and fiom the above named rivers. The samples were collected in two parts, the dry and rainy seasons. Gas chromatography (G.C.) employing the electron capture detector ((ECD) was used for the analysis of the extracted pesticide samples. In the extraction of the collected samples 15% diethylether in hexane was used. , Analysis of the organochlorine pesticide residues was done for l,l-dichlro-2,2- bis (heptachloro)-3,9,4,7,7-tetrahydro-4,7-methanoindene [DDD], l,l-DICHLORO-2,2- bis (p-chlorophenyl) ethylene [DDE], l,l,l-trichloro-2,2- bis (p-chlorophenyl) ethane [DDT], Lindane, Methoxychlor and heptachlor. From the analysis, levels ot‘ these pesticides tend to increase during the rainy season. it is therefore true to conclude that pesticide residues increase with rains.Rivers;Njoro, Makalia and Nderit are the possible sources of the organochlorine pesticides named above. All the pesticides named in this study were detected in samples collected from river Njoro, with methoxychlor as the highest pollutant [4433.5 ppb]. DDD,DDE and methoxychlor were found in samples collected from river makalia_ with DDD [4700 ppb] as the highest pollutant, River Nderit had DDE [62556 pb] as the only pollutant. The other possible source is the town sewerage whose samples were detected to have DDE, DDD and DDT v From the analysis, it can be noted that sediments contain the highest concentrations of the organochlorine pesticide pollutants. Rivers, Njoro, Makalia and Nderit are the major sources of the organochlorine pesticide that find their way into the Lake, while the town sewerage also contributes to the lake’s pollution, Of the 88 samples collected for analysis in the period of April-November, 1999, 6% had DDD, 10% had DDE, 6% had DDT, l4% had Lindane, 3% had heptachlor and 4.5% had methoxychlorl It can therefore be concluded that Lindane seems to be the highest pollutant of the lake Followed by DDT, DDD and DDE; with Heptachlor as the least amongst the pollutants‘