Browsing by Author "Getenga, Zachary M"

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Behavior of pesticide residues in agricultural soil and adjacent River Kuywa sediment and water samples from Nzoia sugarcane belt in Kenya
(Springer, 2012) Muendo, Boniface M; Lalah, Joseph O; Getenga, Zachary M
An inventory survey conducted to determine pesticide usage in a sub-catchment of the Nzoia sugarcane belt found a variety of pesticides used in the sub-catchment, which are reported in this paper. Analysis of soil samples from seven fallow experimental field plots left uncultivated for various periods from 3 to 96 months after cultivation with pesticide application indicated persistence of high concentrations of pesticide residues in the soil, with estimated soil half-lives (in years) ranging from 0.72 to 57.75 for organochlorines and from 1.13 to 8.25 for herbicides. The mean water concentrations (in μg/L) of the pesticide residues in River Kuywa, which flows through the Nzoia Nucleus Estate sugarcane farms, ranged from 0.12 (lindane) to 1.36 (p,p′-DDT) for organochlorines and from 0.14 (atrazine) to 1.75 (diuron) for herbicides during the heavy rains period in August 2008 while the mean sediment concentrations (in μg/g) ranged from 0.28 (lindane) to 1.87 (endrin) for organochlorines and 0.39 (hexazinone) to 4.61 (alachlor) for herbicides. The mean concentrations of residues in water during the light rain period in December 2008 ranged from 0.17 (p,p′-DDT) to 0.71 (aldrin) for organochlorines and 0.01 (atrazine) to 1.74 (alachlor) for herbicides while the sediment concentrations ranged from 0.38 (p,p′-DDT) to 1.145 (aldrin) for organochlorines and 0.74 (atrazine) to 1.98 (alachlor) for herbicides. Although DDT, aldrin, dieldrin, and endrin were not reported in the survey, their presence in the fallow experimental field plot soils and in River Kuywa water and sediment could indicate previous application, lack of recorded data or illegal usage since 1997 when they were banned. Notably, the concentrations of alachlor, diuron, cypermethrin, and hexazinone in the water column were substantial indicating their extensive usage and residual persistence in the sub-catchment, with subsequent wash-off and leaching into River Kuywa. The concentration levels of some of the individual pesticides exceeded the EU limit requirements for drinking water and indicated potential risk to humans and cattle if the water is used without treatment.
The dissipation of hexazinone in tropical soils under semi-controlled field conditions in Kenya
(2009) Lalah, Joseph O; Muendo, Bonface M.; Getenga, Zachary M
The dissipation of hexazinone (Velpar) in two tropical soil types in Kenya was studied under field and semi-controlled conditions for a period of 84 days. The dissipation was found to be very rapid and this could be attributed to adverse weather conditions including high initial rainfall as well as to low soil-organic-matter content, volatilization, surface run-off and biodegradation. The DT50 values of dissipation obtained by first order kinetics were 20 days and 21.3 days in clay and loam soil types, respectively. The influence of bargasse compost (1000 μg/g dry soil) was also studied and was found to enhance dissipation to some extent, giving DT50 values of 18 days and 18.3 days in clay and loam soil types, respectively.
METRIBUZIN SORPTION DYNAMICS IN ACID SOILS OF NZOIA SUGARCANE ZONE IN WESTERN KENYA
(2011) Lagat, Silas C; Lalah, Joseph O; Kowenje, Chrispine O; Getenga, Zachary M; Chepkui, Richard
The adsorption, desorption and leaching of metribuzin in agricultural soil samples taken from Nzoia sugarcane farming area in Kenya were determined using standard methods. The Freundlich adsorption isotherm constants (Kf and 1/n) were found to be 0.54 µg/g and 0.61 µg mL-1, respectively. 94.9% of the residues were recovered after 6 hours of the desorption test and 93.7% of applied dose was found in the leachate after 9 hours of leaching in a soil column. The adsorption curves indicated L-type of adsorption for 0.1, 1.0 and 2 µg L-1 initial pesticide concentrations and S-type for the 5 ppm initial concentration with peak equilibrium adsorption established after 4 hrs of exposure for the 0.1, 1.0, 2.0 µg L-1, respectively, and after 6 hours for the 5 µg L-1 initial concentration. Although the metabolites were not determined, HPLC analysis showed that degradation was rapid and started to occur after 4 hours of exposure, influencing its adsorption isotherms