| dc.description.abstract | In this study water, sediment and weed samples obtained from Tana River in the upper Tana
catchment were screened for chlorpyrifos and organochlorine (OCs) pesticides. The main
concern of this study was to investigate the water quality in Tana River in the Upper Tana
catchment. This is because of intense crop and livestock farming activities and high rate of
industrialization processes taking place in the area. The pesticides residue levels were then
correlated with the physico-chemical parameters in water samples. A total of 720 samples of
water, sediment and weed were analysed for two years from ten sampling points. The river
profile was divided into three sections; upstream, mid-stream and downstream. The extraction of
water samples was done by liquid-liquid partitioning method using dichloromethane, while
sediment samples were extracted in hexane and acetone solvents by soxhlet extraction method.
The extraction of weed samples was done using an orbital shaker in acetone. The analysis of the
pesticides was done using Gas chromatography-mass spectrometer and the data analysis
conducted using Microsoft excel and Pearson’s correlation Statistical Package for Social
Scientists. The concentration of the OCs in water samples ranged from <0.00012 to 107.33 μg/L
with p,p’-DDT with the highest mean residue level observed at Point 7 (Kiganjo) located at the
mid-stream section. Sediments samples had OCs concentration ranging from < 0.00024 to
190.07 μg/kg. These levels were greater than those found in water samples. On the other hand
the residue levels of the OCs detected in weed samples ranged from < 0.00012 to 28.82 μg/kg.
Generally, there was an increasing trend in levels of individual OCs as well as the total OCs in
the mid-stream in all the three matrices. The concentrations were higher during the dry seasons
than in the wet seasons. Chlorpyrifos mean residue levels varied between < 0.0001 and 6.80
μg/kg. The highest mean residue level of 6.80 μg/kg was detected at Point 5 (Tetu). On the other
hand chlorpyrifos mean residue levels found in sediment samples (< 0.0001 -1.43 μg/kg) were
generally lower than those detected in water samples. Mean Chlorpyrifos levels in weed samples
ranged between < 0.0001 and 2.57 μg/kg, with the highest concentrations observed at point 7
(Kiganjo) which is situated at the midstream. pH in water samples ranged between 6.71 and 7.54
which falls within the range of 6.5-8.5 levels for natural water bodies recommended by the
European Union. Electrical conductivity ranged between 57.02 μS and 373.43 μS, with high
mean levels observed at the mid-stream. The correlation of water samples from the upper Tana
River showed high positive values for organochlorine pesticides and the physico-chemical
parameters. For example a high positive correlation coefficient of 0.925 was observed between
OCs and Salinity. | en |
