Decomposition of Residual Captafol in Homogenized Preparations of Fruits and Vegetables

Abstract

During the course of analyses of fungicide residue, it was found that captaf of (N-[1, 1, 2, 2-tetrachloroethylthio]-4-cyclohexene-1, 2-dicarboximide) was decomposed in homogenized preparations of vegetables and fruits. Captaf of was rapidly decomposed in homogenized Japanese radish roots, spinach, and cucumber fruits. When added at 1 ppm level, almost all the compound disappeared within 10 min. Fast decomposition occurred also in cabbage, muskmelon, satsuma orange peel, greenpepper fruit, potato tuber, and onion. Relatively slow decomposition was found in strawberry, tomato, apple, and orange; half lives being 60 min or more. Among 13 vegetables and fruits tested, there was a good linear relationship between pH value of the homogenized preparations and their decomposition activities. As pH value of preparations becomes higher, the decomposition activity increases. The similar pH-decomposition rate relationship was observed within a series of the cucumber fruit juice adjusted the pH from 3. 0 to 7. 5. The decomposition activity in the cucumber juice was dialysable and heat-stable, and the decomposition rate increased with an increase in temperature. These results suggest that the decomposition reaction is non-enzymatic, and that plant constituents with low molecular weight participate in this reaction. An additional evidence was that the decomposition occurred in aqueous solution of thiol reagents such as glutathione (reduced) and cysteine, like in the cucumber juice. For preventing the decomposition of captaf ol, the addition of acetonitrile, hydrochloric acid or masking reagents of thiol group such as trichloroacetic acid, to vegetables and fruits prior to homogenization was effective. Three related fungicides, captan, folpet, and dichlone also were rapidly decomposed in homogenized cucumber fruit. © 1978, Pesticide Science Society of Japan. All rights reserved.