In-house pesticide residue monitoring of tomatoes from souss-massa (Morocco) and pesticide residue levels in tomatoes grown in a greenhouse after multiple applications of dicofol and difenoconazole

A study was undertaken to evaluate the rate of decline of the residues of dicofol and difenoconazole in a Daniela tomato variety grown in an experimental plastic greenhouse. These two pesticides were selected on the basis of previous excesses of 22 and 25%, respectively, found in tomato samples cultivated in 2005 in eastern Morocco. Each group of tomatoes was subjected to a single chemical treatment when close to ripeness; pesticides were applied at the doses recommended by the manufacturers. Fruit samples were periodically collected until the end of the preharvest interval (p.i.). Residue levels of dicofol and difenoconazole were determined by liquid-liquid extraction (LLE), solid phase extraction (SPE) and gas chromatography with electron capture detection (GC-ECD). Residue levels of dicofol ranged from 1.54 to 0.26 mg/kg and the levels of difenoconazole ranged from 2.00 to 0.28 mg/kg, with median values of 0.82 and 0.99 mg/kg, respectively. The residual concentrations after the p.i. were below the legal limits. The difenoconazole value was high in the tomato plants of group VI, which were also treated with copper sulfate. This result indicates that extreme care must be taken when spraying doses of this fungicide, particularly on tomato varieties that are to be used fresh.