Pesticide residues in tomatoes and okra grown on the shores of Pece stream in Gulu Municipality, Northern Uganda

Abstract

This study determined the levels of pesticide residues (cypermethrin, chlorpyrifos, aldrin, dieldrin, dicofol, α-endosulfan and β-endosulfan) in thirty vegetable samples (15 tomatoes and 15 okra) from the shores of Pece stream, in Gulu Municipality, northern Uganda. Extraction of the samples were done using acetonitrile and citrate salts while clean-up was done by use of anhydrous magnesium sulphate, Primary Secondary Amine (PSA) and Graphatised Carbon Black (GCB). The analysis of sample extracts was done using a Gas Chromatograph (GC) equipped with an Electron Capture Detector (ECD). Confirmation of analytes was done by use of GC coupled to a mass spectrometer detector (MSD). The limits of detection (LOD) of the pesticides were in the range of 0.1 to 0.4 µg kg-1. The samples were considered positive for pesticide residues when their residue levels were ≥ LOD. The recoveries obtained from spiking organically grown vegetable samples varied from 71 to 78% and 81 to 94% in okra samples at spiking levels of 100 and 500 µg kg-1, respectively. For tomatoes the recoveries ranged from 70 to 76% at spiking level of 100 µg kg-1 and 81 to 96% at spiking level 500 µg kg-1. The mean residue levels for the pesticides ranged from 1 to 152 µg kg-1 and 7 to 105 µg kg-1 for tomatoes and okra, respectively. Dieldrin was the most dominant pesticide in tomatoes (contributed 52.2% to the total summation of pesticides) while chlorpyrifos was dominant in okra (contributed 27.3% to total summation of pesticides). Vegetables were found to be contaminated with pesticide residue with hazardous risk index (HRI) for dieldrin 4.41 in tomatoes and 2.61 in okra. HRI greater than 1 is considered as not safe for human health. These results show that the main health risk may be posed by consumption of okra and tomatoes from the shores of Pece stream in respect to dieldrin while the remaining pesticide residues present minimal risk.