Pesticide residues in tomato grown in open field

A study was undertaken to evaluate the decline of the residues of benalaxyl, chlorothalonil and methomyl in a variety of processing tomato grown in open field. Tomato plants were subjected to a single chemical treatment, when fruits were close to ripeness, by applying pesticides at the doses recommended by the manufacturers. Fruit samples were periodically taken until the end of the pre-harvest interval (p.i.). The pesticide residues were extracted using acetone and dichloromethane as solvents and determined by gas (benalaxyl and chlorothalonil) and liquid (methomyl) chromatography. The results obtained showed that all the active ingredients had a degradation of first-order kinetics. The residual concentrations after the p.i. were below the legal limits, nevertheless, the value for benalaxyl seemed to be rather high. This finding indicates the need for careful control of the spraying doses of this fungicide, in particular on varieties of tomato which are used fresh.