In order to check the pre‐harvest intervals established in Portugal for olive trees, residue dissipation studies have been carried out for the organophosphorus insecticides diazinon, dimethoate, methidathion, parathion and phosphamidon. Simul‐taneously with the analyses of the olives, olive oil produced in the laboratory by a mechanical procedure of pressing the olives was also analysed. The analyses were car‐ ried out by gas‐liquid chromatography. Residues found in the fresh olives, sampled at the end of pre‐harvest intervals in force for each of the insecticides, were accept able. However, for diazinon and parathion, unacceptable high residue levels were found in the olive oil. The concentration of methidathion residues in the olive oil was also observed. For dimethoate and phosphamidon, no detectable residues were found in the olive oil, even when the olives were sampled one day after spraying.

The influence of surface of exposure of brassicas to insecticide sprays has been assessed in two experiments conducted in small plots where endosulfan, parathion, trichlorfon and pirimicarb were applied to a flowering brassica, broccoli (Brassica oleracea L. var italica Plenck) and to a leafy brassica (Brassica oleracea L. var. tronchuda Bailey). The differences of surface exposure resulted in much higher deposits and subsequent residue levels in broccoli. The results stress the need to evaluate residue data on groups of brassicas of different surfaces of exposure to pesticide spray when granting registration petitions for brassicas in general in order to establish pre‐harvest intervals.

A method intended for regulatory purposes is described for the determination of organophosphorus insecticide residues in fruits and vegetables. Eighteen organophosphorus insecticides, azinphos-ethyl, chlorpyrifos, diazinon, dichlorvos, dimethoate, ethion, ethoate-methyl, fenitrothion, fenthion, formothion, malathion, methidathion, mevinphos, parathion, phosalone, phosphamidon, thiometon, and trichlorphon, and 7 metabolites, fenitrooxon, fenthion sulfoxide, fenthion sulfone, malaoxon, desethylphosphamidon, thiometon sulfoxide, and thiometon sulfone, were extracted from different crops with acetone and partitioned into hexane or ethyl acetate, according to their polarities. The hexane extract was cleaned up by eluting from a Florisil column with acetone-hexane (4+96). The ethyl acetate extract needs no cleanup. The concentrated extracts were analyzed by gasliquid chromatography using thermionic detectors. Recoveries conducted at fortification levels ranging from 0.1 to 2 mg/kg were in most cases above 80%. The limit of sensitivity is less than 0.1 mg/kg.

Repeated applications of dimethoate were carried out on peaches and apple trees in order to establish the maximum number of dimethoate sprays that will give rise to residues complying with international maximum residue limits. Samples were analyzed by gas chromatography for the determination of dimethoate and its oxygen analogue, omethoate, over a period of 3-4 weeks after last spray. Only in the case of apples with seven applications, mean residues of dimethoate exceeded 1 ppm at the end of the preharvest interval (14 days); residue levels of omethoate were always below 0.2 ppm. Considering the eventual need of a preharvest interval not longer than 14 days, restrictions on the number of applications during apples growth cycle should be enforced.

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