Abstract:
The noxiousness of pesticides as well as their harmful environmental effects have
generated interests in the identification and quantification of organic contaminants in
borehole water. These contaminants can move from agricultural land or poorly managediv
sewerage systems and get into drinking water by surface runoff or by leaching into
groundwater. The study sought to analyze the organic contaminants and their effects on
physico-chemical parameters of borehole water of Maili-nne; a residential area and
Sosiani, an agricultural area. This was through detection of organic contaminants in
borehole water; quantification of the detected organochemicals; and establish the impacts
on the physico-chemical properties of borehole water of Maili-nne and Sosiani areas.
Fifteen boreholes, five at Maili-nne (MB1-MB5) and ten at Sosiani (SB6-SB15) were
systematically selected and water sampled during the dry and the wet seasons. Organic
contaminants were analysed by detection and quantification of organic pesticides and
plasticizer based on retention times by High Performance Liquid Chromatography
(HPLC) and Gas Chromatography–Mass Spectroscopy (GC-MS) in correlation to
computed element libraries for quantification. Their impact on pH, turbidity, colour and
Biological Oxygen Demand (BOD) were probed using pH meter, turbidity meter, colour
disc and BOD meter, respectively. The nutrients, sulphates and nitrates were analyzed
using ultraviolet spectroscopy (UV-Vis). Diazinon was detected in boreholes SB9, SB12
and SB13, with highest level of 2.21 mg/L during the dry season and 1.52 mg/L in the
wet season. Fenitrothion was detected in MB1 (0.145 mg/L and 0.191 mg/L) during the
dry and the wet season, respectively. Malathion was found in SB6 and SB15 at 0.207
mg/L and 0.940 mg/L, respectively only during the dry season. Cyhalothrin concentration
in MB1, SB7 and SB9 were 0.11, 1.25 and 1.47 ppm, respectively during the dry season
and 1.37, 1.31 and 1.21 ppm, respectively during the wet season. The concentration of bis
(2-ethylhexyl) phthalate in the 15 boreholes ranged from 0.00 μg/L to 0.172 μg/L.
Dimethoate was only detected in Sosiani (SB7) during the wet season. Sulphates
concentration ranged between 0.00 -28.3 mg/L during the dry season and 1.06 - 66.44
mg/L during the wet season in Maili-nne and Sosiani. Nitrates concentration ranged
between 0.31 - 22.8 mg/ L in the dry and the wet seasons. Physico-chemical properties of
the water were found to be higher and others lower than WHO standards. The pH of the
borehole water was in the range 5.45 - 5.92. Turbidity ranged between 1.32 - 3.08 NTU
and 1.23 - 6.42 NTU during the dry and the wet seasons, respectively. BOD values
ranged from 1 - 40 mg/L in the wet season and 0 – 8mg/L during the dry season and were
significantly lower in Sosiani than in Maili-nne during the wet season. It can therefore be
concluded that residues of some organic contaminants were above the WHO standards
leading to decrease of water pH during the dry season beyond WHO limits (pH 6.5). The
study also established that there was a positive significant correlation between presence
of organic contaminants and deviation of physico-chemical properties (p=0.016,
rho=0.68) in Maili-nne and Sosiani. In this regard the borehole water in the study areas
should be treated and awareness be made on the impacts of pesticides use.