Radiotracer study on mancozeb residues in tomato plants

A study on the persistence, residues and residue distribution of mancozeb in tomato plant-soil system, as well as effects of cooking on transformation of residual mancozeb were carried out with radiotracer technique. Half-life values for total mancozeb residues on tomato leaves and in soil were observed to be 9.5 and 7.6 days, respectively. The results also suggested that mancozeb residues in soil were readily uptaken by plants and leach to soil layer as deep as 28cm within two weeks, although over 90% of the residues remained in the upper layer (0-6cm) of the soil. Translocation of the residues of mancozeb, especially the water soluble metabolites including ETU, throughout the plants could be one of the factors responsible for the contamination of tomato fruits. Deposit of sprayed mancozeb on the fruit skin was another important factor leading to the contamination of fruits. Fruit skin contained higher levels of residues than the pulp. Washing with water could remove more than 50% of the residues on the skin. It was also found that 20-30% of the residual mancozeb degraded to ETU during cooking process. The tomatoes should be washed to reduce the residues of the fungicide and ETU in food.