Fehlermöglichkeiten bei Rückstandsuntersuchungen von Gemüse und Obst- bedingt durch die Probenahme

Mistakes in the results of residue analysis in vegetables and fruits based on samples Mistakes in the results of residue analysis can be separated into mistakes of sample-taking and those of analysing. The mistakes of sample-taking can be avoided when the sample represents the contents of the whole material which is to be analysed in percent. But this is an ideal case.In two examples, lettuce and leek, it is demonstrated that the pesticides are not in the same amount distributed at the different zones of the plant, the differences in the amounts can be, in the case of lettuce after application of quintozene, more than a fourtyfold amount or, in the case of leek after application of mancozeb, a twentyfold amount. Furthermore, the residues can be different from one plant individual to another demonstrated at cherries and radishes. The differences may be caused either by different application techniques or, for example, by different weight of individuals of the same species. Also, different habitus and growth can lead to different residues from one plant individual to another. When the plants take up the pesticides from the soil, a different pesticide distribution in the areas of the soil can also give rise to different residue values.Therefore, the man (engineer or analyst) who takes the samples, must take care for:1. taking the samples symmetrically from the field or from bottom to top of the trees2. chosing those plant individuals to give the labour sample which represent the average weight and the average habitus of the individuals. If plant individuals are analysed which take up the pesticides from the soil, the area from which the sample is derived, must be given.From all points shown, there is clear that a range of disseminating values which can be more than 100% must accounted in the values of residue analysis.