The effectiveness of common washing methods in reducing mancozeb pesticide on tomatoes sold in selected markets around Kampala

Abstract

The widespread use of mancozeb a di thiocarbamate broad spectrum fungicide, in tomato farming has raised concerns due to its potential to leave harmful residues on produce. In Uganda, where tomatoes are a dietary staple, limited data exists on the actual levels of mancozeb in consumer ready tomatoes especially in relation to common house hold washing methods. While international studies have explored the impact of washing on pesticide residues, there is a significant gap in localized data addressing residue levels in washed and unwashed tomatoes sold in Kampala's major markets. This study evaluated the effectiveness of common washing methods, tap water, distilled water, and vinegar in reducing mancozeb pesticide residues on tomatoes sold in three major Kampala markets: Nakawa, Kalerwe, and Kasubi. The tomatoes were collected from three markets, and the quantification of mancozeb resides was done using UV-Vis spectrophotometry. A Calibration curve was generated using commercial Mancozeb and this was used to calculate sample concentrations, expressed in mg/kg. Results were statistically analyzed using paired t-tests and one-way ANOVA. The results revealed that unwashed tomatoes had the highest mean residue levels (3.2 mg/kg) exceeding Codex MRL for di thiocarbamates in tomatoes which is 2mg/kg, while washing with vinegar yielded the greatest reduction (0.87 mg/kg, ~71.67% reduction), followed by tap water (1.15 mg/kg, ~64.64%) and distilled water (2.02mg/kg, ~37.21%). All reductions were statistically significant (p < 0.05), with vinegar showing the highest effectiveness in reducing Mancozeb residue levels. These findings suggest that washing with vinegar or tap water significantly reduces mancozeb residues to safer levels, offering practical implications for public health and food safety. The study highlights the need for awareness campaigns on pesticide usage and regulatory enforcement to enhance food safety in Uganda's urban markets.