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Title of Thesis

Barkat Ali Khan
Institute/University/Department Details
Nwfp Agricultural University/Agricultural Chemistry
Agricultural Chemistry
Number of Pages
Keywords (Extracted from title, table of contents and abstract of thesis)
pesticides, agricultural practices, residues, vegetables, fruits, cypermethrin, methamidophos, chlorpyriphos,

The use of pesticides is one of the essential measures of modem agricultural practices in protecting the crops from different pests. On the other hand the residues resulting from the misuse of pesticides on vegetables and fruits is a major concern in many countries as well as in Pakistan. However, the hazards to health can be minimized to a great extent if these residues are kept below their prescribed safe level (Maximum residue limit). A field survey was conducted in the major growing areas of fruit and vegetables in Peshawar regarding the use of insecticides by local farmers on these crops. On the basis of questionnaires, 105 (70 vegetable and 35 fruit) farmers were interviewed concerning the types of insecticides used, the frequency and doses of application, and the time of insecticide application prior to harvest. Fifteen insecticides belonging to different groups were found to be commonly used on fruits and vegetables by the respondent farmers. Of these, the most frequently used insecticide was cypermethrin followed by methamidophos and chlorpyriphos.

In order to assess the residue levels of insecticides in fresh fruit and vegetables, samples were collected at harvest from the fields/orchards of the farmers at about 100 different sites in Peshawar. The analysis of insecticides was limited to the treatment history obtained from the vegetable and fruit grower. The samples were extracted in ethyl acetate. The extracts were cleaned up through Florisil column with ethyl acetate as eluent. Four HPTLC techniques namely, (i) o-toluidine + KI (ii) aluminum oxide G incorporated with silver nitrate (iii) enzyme inhibition with cow liver extract and β- naphthyl acetate substrate and (iv) enzyme inhibition with horse blood serum and acetylthiocholine iodide substrate were used for residue analysis. Six hundred and eight samples of vegetables and fruits were analysed using these HPTLC methods. The most commonly detected residues were those of methamidophos (9.8% of 608 samples), cypermethrin (8.5%), endosulfan (4.9%), chlorpyriphos (4.4%), trichlorfon (3.3%), methidathion and methomyl (2.8%), dimethoate (2.6%) and λ-cyhalothrin (1.8%) depending on the type of insecticide being used by the grower. Of all analysed fruit and vegetable samples (608), 250 samples (41%) contained detectable residues. Of these, 13.8% had residues that exceeded Codex maximum residue limits (MRLs). For individual crops, contaminated samples ranged from 10 to 100 % of the number of samples analysed.

Six supervised trials were conducted on three vegetables, viz. tomato, okra and cauliflower and three fruit crops, viz. guava, apple and peach during 2000-02 to study residue dissipation rates of eight insecticides after application to these crops under agro climatic conditions of NWFP. The insecticides selected for field experiments were five organophosphorus insecticides (methamidophos, dimethoate, methidathion, trichlorfon and chlorpyrifos); and one each of pyrethroids (cypermethrin), carbamates (methomyl) and organochlorines (endosulfan). Experiments on okra, cauliflower, tomato, and peach were conducted at the farm of the Agricultural Research Institute, Tarnab, Peshawar, while experiments on guava and apple were conducted on farmers' orchards in Kohat and Swat, respectively.

For each vegetable, triplicate (2 kg per field replicate) samples were randomly collected from supervised trials at 0 (1 hr after spray), 1, 3, 5, 7, 10 and 15 days after insecticide application. The treated fruits of guava, apple and peach were randomly sampled in triplicates (2 kg per field replicate) at intervals of 0, 3, 7, 14, and 21 days after treatment. The samples were extracted in ethyl acetate and were cleaned up through Florisil column with ethyl acetate as eluent. The cleaned up extracts were analysed for residues with both HPTLC and HPLC methods. Recoveries of the 8 insecticides from 6 crops fortified at 0.1-3.0 mg kg-1 were 59-103 %.

The number of days for residues to drop below tolerance limits was highly dependent on the magnitude of the initial residue. Large variations in initial residues were observed between years, between insecticides and between crop types. Organophosphate residues were found to have half-lives of 9.0 to 12.0 days for methamidophos, 6.8 to 8.8 days for dimethoate, 13.3 to 26.0 days for trichlorfon, 3.6 to 14.8 days for chlorpyriphos and 7.5 to 15.2 days for methidathion. The half-life of cypermethrin was 6.0 to 18.5 days, for methomyl it was 1.5 to 3.4 days and for endosulfan it was 3.7 to 4.6 days. Based on the dissipation pattern of residues from different insecticides in relation to their respective prescribed maximum residue limits, withholding periods of 11-13 days for cypermethrin and of 2-3 days for methomyl for tomato; 10-15 days for cypermethrin and 3-4 days for endosulfan for okra; and 9-12 and 7-9 days for cauliflower after treatment with methamidophos and cypermethrin were suggested. Withholding periods of 8-10 and 23- 26 days were suggested for peaches after treatment with chlorpyriphos and trichlorfon. Apples treated with methidathion and chlorpyriphos, exhibited withholding periods of 12-15 and 7-14 days respectively. The withholding periods were respectively 13-14 and 7-8 days for guava after treatment with trichlorfon and dimethoate.

Download Full Thesis
2443.45 KB
S. No. Chapter Title of the Chapters Page Size (KB)
1 0 Contents
160.21 KB
2 1 Introduction 1
73.42 KB
  1.1 Background 2
  1.2 Justification 3
  1.3 Objectives 7
3 2 Review Of Literature 9
301.37 KB
  2.1 Monitoring of pesticide residues in fruits and vegetables Collected from market and growers' fields 9
  2.2 Pesticide residues in fruit and vegetable samples from Supervise trial
  2.3 Analytical techniques used for pesticide residue analysis 22
4 3 Materials And Methods 42
198.03 KB
  3.1 Field Survey 42
  3.2 Sampling of fruits and vegetables for pesticide residues 44
  3.3 Field experiments 48
  3.3.1 Choice of pesticides 8
  3.3.2 Vegetables 50
  3.3.3 Fruits 51
  3.3.4 Meteorological data 53
  3.3.5 Field Sampling 53
  3.4 Methodologies employed for pesticide residue analyses 54
  3.4.1 Extraction of pesticide residue from fruits and vegetables 54
  3.4.2 Clean up of extracts of pesticide residues on Florisil column 55
5 4 Results 63
581.79 KB
  4.1 Field Survey 63
  4.1.1 Fruit and vegetable growers 64
  4.1.2 Pesticide dealers 68
  4.2 Validation of chromatographic techniques 70
  4.2.1 Validation of Thin Layer Chromatographic (TLC) methods 70
  4.2.2 Standardization of HPLC 76
  4.3 Pesticide residues in vegetables and fruits by HPTLC Methods 83
  4.3.1 Residues in vegetables 83
  4.3.2 Residues in Fruits 91
  4.4 Field experiments 99
  4.4.1 Residues of methomyl and cypermethrin in tomatoes 99
  4.4.2 Residues of endosulfan and cypermethrin in okra 105
  4.4.3 Residues of methamidophos and cypermethrin in cauliflower 110
  4.4.4 Residues of dimethoate and trichlorfon in guava 115
  4.4.5 Residues of met hid at hi on and chlorpyriphos in apples 120
  4.4.6 Residues of trichlorfon and chlorpyriphos in peaches 125
6 5 Discussion 130
97.98 KB
  5.1 Validation of TLC Methods 130
  5.2 Recovery studies by HPLC 131
  5.3 Field Survey: Pesticide residues in vegetables and fruits Collected from growers' fields/orchards using HPTLC Methods 132
  5.4 Field experiments: Analysis of field treated samples of fruit and Vegetable from supervised field trials using HPTLC and HPLC methods 135
7 6 Summary 141
37.75 KB
8 7 Conclusions 145
19.38 KB
9 8 Recommendations 147
877.26 KB
10 9 Literature Cited 149
196.66 KB
11 10 Appendices 171
155.69 KB