The temporal variation in pesticide residues in Kampos, of Chios Island, in Greece, was determined between June 2014 and October 2019. Monitoring of residues took place before and after the development of an Integrated Pest Management Strategy (IPMS) for the sustainable control of the Mediterranean fruit fly (medfly) based on mass trapping with the non-toxic and environmentally friendly attractant Biodelear. A total of 1252 samples of citrus fruits, collected from 12 experimental citrus orchards, were analyzed for the presence of 353 active substances and metabolites of pesticides. A modified QuEChERS method and sensitive chromatographic techniques were used. During preparatory monitoring for the project, the most frequently detected pesticides were the insecticides chlorpyrifos, deltamethrin and spirotetramat; the fungicides propamocarb, dimethomorph and mepanipyrim; and the synergist piperonyl butoxide. The implementation of the IPMS to address medfly resulted in a dramatic reduction in the pesticides detected in citrus fruits during confirmatory monitoring, with no detectable residues—which may cause serious problems to human health—in any of the samples analyzed at the end of the project, thus enhancing consumer safety.

The Carry over effect, i.e. the appearance of a peak in the chromatogram of a blank analysis due to sample remaining from the previous analysis, was studied. The study was conducted for pesticide residues analysis by LC-MS/MS. In total 128 pesticides that belong to 13 different chemical classes were analyzed in order to investigate the cases that the effect is significant; i.e. a peak higher than 1% of the peak of the previous chromatogram appears. Carry over was found for 32 of the 128 studied pesticides (25%), at concentration levels between the LOD and 0.167 μg/mL. For 28 out of the 32 substances, more than two injections of a blank sample were required, as to reduce the effect significantly. Compounds presenting Carry over effect were mainly non-polar with logkow values between 4 and 7, characterized with very low water solubility, between 0.001 mg/L and 2 mg/L. On the contrary, the vapor pressure did not seem to be obviously related to the effect, as the substances presenting Carry over had various vapor pressure values, from 10-12 to 0.2 mP.

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