Determination of Some Herbicide Residues in Sweetpotato

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Weeds are undesirable in agriculture activities since they compete with food crops for available soil nutrients, air, water, sunlight and space. Reports indicate that when these herbicides are applied, only about 1% is effective whereas the remaining 99% exist as residues in the surroundings thus posing serious threats to human health, the environment, wildlife and other non-target organisms. The objective of this work was to determine the level of some herbicide residues in sweetpotato. The sweetpotatoes were cultivated in a completely randomized block design (CRBD) with four replications at the Crops Research Institute Agronomy fields, Kwadaso where different treatments made up of combinations of five (5) pre-emergence herbicides (butachlor [50g/L-3L/Ha], imazethapyr [240g/L-3L/Ha], metolachlor [333g/L-4L/Ha], pendimethalin [500g/L-3L/Ha] and terbutryn [167g/L-4L/Ha]) and one (1) post-emergence herbicide (propaquizafop [100g/L-1.2L/Ha]) were applied and a control which involved strictly hoeing. After harvest, samples were randomly selected and extracted using a modified QuEChERS extraction method followed by Liquid Chromatography-Mass Spectrometry (LC-MS) to determine the residual levels of the herbicides. The results showed that sweetpotato samples from the control (field work which was strictly hoeing as the method of weed management) had no residues detected. Butachlor, imazethapyr, terbutryn and propaquizafop were also not detected in their respective sweetpotato samples analysed. However, pendimethalin and metolachlor residues were detected at concentrations of 0.0023 µg/g and 0.0029 µg/g, respectively. The findings suggest that herbicide residue levels detected in this study were considerably lower than the maximum acceptable limit (0.05 mg/kg) and thus the dietary exposure could be considered safe to humans.
A thesis submitted to the Department of Food Science and Technology, College of Science, in partial fulfillment of the requirements for the degree of Master of Science in Food Quality Management.