[The method of removing methamidophos from contaminated vegetables]

Since the massive food poisoning outbreak in 1987, imported vegetables contaminated with methamidophos continued to cause sporadic food poisoning outbreaks in Hong Kong. Despite various administrative measures to lower the risk of importing vegetables, it is evident that the occurrence of sporadic food poisoning outbreaks cannot be completely stemmed out. The education of the public on the effective ways to remove methamidophos from the contaminated vegetables was reckoned to the another preventive measure against food poisoning. A study was carried out to evaluate the effectiveness of various ways of treating the vegetables before consumption. In this study, the removal of methamidophos by simply washing with water at near room temperature was found to be a slow process. The concentration of methamidophos was reduced by about 65% after washing in water for an hour. Further washing did not improve the situation. The addition of detergents and various washing aids including potassium permanganate, hydrogen peroxide, sodium bicarbonate and vinegar did not greatly enhance the removal effectiveness. Among the various treatment procedures, soaking in hot water was the most effective way to remove methamidophos from vegetables. Less than 10% of the pesticide remained in the vegetables after soaking in boiling water for 1 minute.