Masters Dissertation
In modern agriculture, pest infestation has posed a great challenge to farmers.
The use of pesticide has eventually become an important tool to ensure quality and
quantity of crop yields. However, such chemicals might have residual impacts to
consumers.
This study was conducted to assess the extent of pesticide residues in
harvested tomato fruits at Makambako Town Council in Njombe region, Tanzania.
Specifically the study aimed at: (i) investigating adherence to recommended
manufacturer’s instructions on pesticide application among tomato farmers (ii)
determining level and frequency of occurrence of selected pesticide residues in tomato
fruits and (iii) characterizing dietary risks associated with consumption of fresh tomato
fruits containing pesticide residues. Forty seven (47) farmers were interviewed on
pesticide types and their application using structured questionnaire. Forty two (42) fresh
tomato fruits for laboratory analysis were sampled from interviewed farmers who were at
harvesting season. QuEChERS (CEN) Method 15662.5 was employed for pesticide
extraction and analyzed by Gas Chromatography Mass Spectrometer. It was found that all
respondents mixed more than one pesticide in a single spray tank without adhering to
recommended mixing procedures. The average withholding period was 5 days, below the
recommended 7 days for mixture of mancozeb and metalaxyl which were commonly used
fungicides at the study area. Eighty three percent of the respondents exceeded the mixing
concentration of pesticide above the recommended mixing ratios. Residues of
chlorpyrifos, profenofos, gamma cyhalothrin and cypermethrin were alternatingly
detected in 78.51 % of analyzed samples. The average concentrations of residues were
0.014, 0.056, 0.003 and 0.2 mg/kg for chlorpyrifos, profenofos, gamma cyhalothrin and
cypermethrin, and were all below Codex MRLs of 1, 10, 0.3 and 0.2 mg/kg respectively,
as per FAO/WHO guidelines. The maximum residue concentration was 0.718 mg/kg for
cypermethrin, which was above the Codex MRL of 0.2 mg/kg. Profenofos was the most
frequently detected pesticide, occurring in 60 % of samples. The hazard indices for the
selected pesticide indicate no potential health hazards to general population due to
lifetime consumption of fresh tomato fruits from the study area. The study recommend
regular training to farmers on good agricultural practices through extension officers and
pesticide regulatory authority. Further research on pesticide residues and dietary risk
assessment is recommended for other pesticide commonly used at the study area.