Degradation and Residues of Dimefuron in Pineapple

Abstract

Dimefuron-¹⁴C (1,1-dimethyl-3-(3-chloro-4-(2-t-butyl-5-oxo-1,3,4-oxadiazolin-4-yl) phenylurea) was applied to Smooth Cayenne pineapple plants (grown from tillers and crowns), at the rate of approximately 2.5 kg ai/ha, at 3 days, 4 and 9 months after planting. Plants were harvested after 16 months and the ¹⁴C-residues were analysed by extraction with acetone, methanol and 0.1 N. HCl/90% methanol respectively. The extracts and bound residues were assayed by liquid scintillation counting and a combustion technique respectively. The results showed that dimefuron and/or its metabolites were absorbed via the roots and /or shoots and transported to the fruits, which developed after application. At harvest the radioisotope was found in all parts of the treated plants. The ¹⁴C-residues expressed as dimefuron equivalents in flesh, peel, crown, stem and leaves were 0.045, 0.049, 0.087, 0.288 and 0.822 µg/g (fresh weight) for the pineapples grown from crowns and 0.064, 0.058, 0.0128, 0.405 and 1.235 µg/g (fresh weight) for the pineapples grown from tillers respectively. In the pineapple flesh 81.3 to 97.8% of the residue was found in acetone and methanol, 0.0 to 12.5% in 0.1 N. HCl/90% methanol and 2.2 to 6.3% as a bound residue.