Adsorption of Fenitrothion in Selected Soils

Adsorption of pesticides and their degradation products in soil due to various physical and chemical mechanisms plays a major role in environmental fate of such chemicals. Over years, farmers in Kenya (more so those from rural areas) have been using pesticides on their farms with the aim of destroying pests but most of them don’t consider the amount (concentration) of the  pesticide applied with regard to their effect on the environment. This chemicals end up contaminating the environment.

Farmers also do apply compost to the farms without thinking about its effect on the adsorption of the pesticide to be used thus they ought to have knowledge on such matters to enable them make wise and informed choices.

This research focuses on the adsorption of fenitrothion in soil samples collected from upper parts of R. Nzoia, R. Nyando and R.Yala and the effect of compost application on adsorption of fenitrothion in the selected soil. It also aims at determining the detectable concentration to be applied to the selected soils samples.

 5ml of fenitrothion solution at different concentrations (100ppm to 800ppm) was added to 1g of each soil sample of the three soil types and shaken at room temperature for 24hrs by use of orbital shaker after which the supernatant separated from the soil suspension after centrifugation at 3000 rev/min for 15 minutes was extracted with 1ml of dichloromethane (DCM) for each sample. The extracts were concentrated with about 1ml isooctane at room temperature then blown by nitrogen to about 1ml in sampler vial for quantitative gas chromatographic analysis.

The results of the peak areas obtained from the GC were used to calculate the amount of the adsorbate adsorbed per unit mass of the adsorbent and then fitted to the Freundlich model (log qe = 1/nlog Ce + log k) to compare the adsorption isotherms for the three types of soils under study.

From the graphs drawn for log qe versus log Ce, the K values for compost free soil samples ny, yl and nz were 90.5941, 55.5520 and 171.1591 respectively while those for composted soil samples nyc, ylc and nzc were 171.1591, 343.7162 and 425.8925 respectively.

From the above results, it is clear that the soil sample nz has the highest affinity for the insecticide than the other two soil samples. It also shows that compost application leads to an increase in each soil sample’s affinity for the insecticide thus much of it is adsorbed by the soil.

Compost application increases soil affinity for the adsorbate thus is recommendable for farmers to apply compost to their farms so as to reduce the amount of the insecticide reaching water sources which in-turn reduces environmental contamination.

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