Evaluation of Organophosphate Pesticide Residues in Selected Vegetables Sold in Nagongera Town Council, Tororo District, Uganda.
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Date
2026-08-31
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Busitema University
Abstract
ABSTRACT.
Organophosphate pesticides are widely used in vegetable production to control pests and diseases, but inappropriate application practices may result in pesticide residues remaining on vegetables intended for human consumption. Monitoring of such residues is important for food safety; however, access to advanced analytical techniques for pesticide-residue analysis may be limited in some local laboratory settings. This study therefore evaluated organophosphate pesticide residues in selected vegetables sold in Nagongera Town Council, Tororo District, Uganda, using an ammonium molybdate UV–Visible spectrophotometric approach.
A laboratory-based analytical study was conducted on tomatoes, cabbage and Sukuma wiki collected from selected markets, roadside vendors and shops within Nagongera Town Council. The samples were homogenized and extracted using analytical-grade acetone. The extracts were subsequently subjected to concentrated sulphuric acid digestion to convert phosphorus associated with the extracted organophosphate compounds into inorganic phosphate. Phosphate standard solutions were prepared from potassium dihydrogen phosphate and used for calibration. The digested samples were treated with ammonium molybdate and ascorbic acid and analysed spectrophotometrically at 670nm.
Measurable concentrations of inorganic phosphate derived from organophosphate pesticide residues were detected in all the selected vegetable types. The concentrations varied among the vegetables, with Sukuma wiki recording the highest mean concentration (33.615 mg/kg), followed by cabbage (27.490 mg/kg), while tomatoes recorded the lowest mean concentration (16.685 mg/kg).
The study demonstrates the potential application of UV–Visible spectrophotometry as an accessible screening approach for inorganic phosphate derived from organophosphate pesticide residues in vegetables, particularly where access to advanced chromatographic instrumentation is limited. However, the method does not identify individual organophosphate pesticide compounds and therefore cannot establish the specific pesticides responsible for the detected residues. Further studies using more specific analytical techniques such as gas chromatography-mass spectrometry (GC-MS) or high-performance liquid chromatography (HPLC) are recommended to identify and quantify individual pesticide compounds. Regular monitoring of pesticide residues and sensitization of farmers on appropriate pesticide-use practices are also recommended to support food safety in the study area.