The fate and residues of Zineb, Maneb, and ETU on fresh and processed tomatoes, beans and cucumbers

The Ethylenebisdithiocarbamates (EDBCs) represent an important group of surface protectant fungicides that are widely used to control a wide spectrum of plant pathogens. These fungicides are chemically unstable; they decompose to yield a variety of products, mainly ethylenethiourea (ETU). Although the EDBCS have a low LD50, toxicological concern has been raised about their use because of their decomposition to ETU which was demonstrated to be carcinogenic, goitrogenic, mutagenic and teratogenic. To find out to what extent ETU is formed or decomposed under greenhouse and local field conditions, the fruits of tomatoes, cucumbers, and beans were sprayed with [C14]zineb or [C14]maneb and assayed for ETU content by liquid scintillation counting. A sharp reduction in ETU content was observed in the firest 24 hours after treatment followed by a slow decrease in the following days and reaching very low levels at day 20th. In fact, the amount of ETU was reduced by about 80% after 20 days. Therefore, the results show that no accumulation of ETU occurs with time on treated crops. The formation of ETU is known to increase during cooking plant material previously treated with the EDBCs. In fortification experiments with [C14]maneb, no change in the amount of ETU was observed after the pickling process of cucumbers. However, there was a 8% increase in ETU content after storage at room temperature for a period of 40 days. As for fate of ETU in processed food, studies with bean pickles and tomato paste fortified with [C14]ETU, just before processing, showed that this compound persisted in the processed products. The ETU content was reduced by about 4% in these products after a storage period of 40 days. With respect to reducing ETU levels on crops treated several times with the commercial EDBCs, washing experiments were conducted at different time intervals after the last fungicide application. As previously reported in the literature, washing the vegetables with water or with soap and water greatly reduced the amount of residues