Dislodgeable residues of methamidophos in staked tomatoes

Abstract

The measurement of dislodgeable pesticide residues is a way of estimating occupational exposure of farmers in their working environment. This study evaluates dislodgeable methamidophos residues on leaves, fruits and soil in staked tomatoes (Lycopersicon esculentum Mill), with the objective of estimating potential exposure. The experiment consisted of four treatments: application of methamidophos in a single rate of 0.6 g a.i. L-1 water; application of a double rate of 1.2 g a.i. L-1 water ; four applications of a single rate; and control. The first spraying in the four-application treatment was made at the beginning of fruit maturation. The later applications followed a 6-day schedule. Spraying of the treatments with one application was simultaneous to the last spraying of the four-application treatment. Leaf, fruit and soil samples were taken one day before applications, and 0, 1, 2, 3, 5, 7 and 14 days after them. Dislodgeable methamidophos residues were extracted by Sur-ten aqueous solution; extracts were partitioned in a methanol-ethyl acetate mixture, and the residues were quantified by gas chromatography on a flame photometry detector. Foliar residues in the four-application treatment at the single rate and one application at the double rate had similar degradations, with half-lives of 0.7 and 0.9 day, respectively. The behavior of soil dislodgeable residues in the treatments at a single rate (one and four applications) was similar, with half-lifes of 2.9 and 2.7 days, respectively. Residues on soil were more persistent than residues on the leaves. Residues on fruits were detected only for 0 and 1-day old samples. Results show that degradation on tomatoes is relatively fast.