The word pesticide is often used as a synonym for the term plant protection product. The pesticide residues we analyze in foods of plant origin are used to protect plants or plant products from diseases, harmful microorganisms and animal or plant pests (e.g. weeds). In particular, their application serves to generate better harvests. Pesticides are usually comprised of mixtures of substances. Their mode of action is determined by the active substances contained therein. Based on their main objective, pesticides are divided into different pesticide classes. The most widely used pesticide classes are insecticides, which are effective against insects, and herbicides, which are effective against weeds. In addition to the active ingredients in pesticides, other substances may be included. For example, co-formulants promote better adhesion or distribution of the pesticide on the plant. Synergists, on the other hand, can increase the effect of the pesticide active ingredient.
If you count all feasible types of pesticides together, there are over 1,400 different pesticides used in the world. However, these include substances that are not very important to us, such as chili extract, bird deterrents or tree remedies. At CVUA Stuttgart we have over 1,000 pesticide reference substances at hand. By using our screening detectors (e.g. GC-Orbitrap, LC-ToF), we can find many of these substances when the quantities are substantial enough. However, our quantitative scope includes over 750 substances that we scrutinize in extreme detail, meaning that we can detect even the smallest of traces of these well-selected substances in foods of plant origin.
Normally, you can’t know whether pesticides were used by relying on your senses (smell, taste and appearance). Occasionally, one sees a droplet-like coating on peppers or grapes, for example. However, this coating can also be quite harmless silica, which the plants use to strengthen their resistance to fungi.
Pesticides are applied to plants in different ways. Some are only present on the surface of the plants (non-systemic) and act as a kind of contact poison. However, many pesticides are absorbed by the plants and are distributed via the vascular system throughout the plant. This has the advantage that the plant is protected even where the spray nozzle hasn’t reached, and that pests can be targeted that are otherwise hard to kill. Pesticides that are only applied to the surface can be reduced by washing, depending on the water solubility of the pesticide. Warm water is better here than cold. However, systemic pesticides that are also distributed within the plant can hardly be reduced.
The coexistence of different pesticide residues in a fruit or vegetable can have different causes. On the one hand, there are several classes of pesticides that work against specific pathogens: herbicides against weeds, fungicides against fungi, insecticides and acaricides against insects and mites. A single pesticide may contain several active substances that complement each other in their action (so-called combination preparations).The use of combination preparations as well as the successive application of various pesticides in crop rotation (for the prevention of resistance, among others) can lead to multiple residues in a food.
The maximum residue levels (MRL) that have been set by the EU indicate the maximum amount of pesticide residues that may be present on a product after a plant protection measure has been properly performed and the waiting period between application and harvest has been adhered to. Thus, maximum residue levels are there to check if the farmer/producer has conducted his work properly when using plant protection products. If the bananas were analyzed for pesticide residues without the peel, compliance with the rules of application in the fields could not be checked. The analysis of the whole fruit also means that we determine the maximum amount of pesticides that the consumer could intake. In fact, the amount of pesticide residues that are consumed are usually less than the analyzed value, because fresh fruits and vegetables are washed, peeled, cut and/or the outer leaves are removed during food preparation.
Each individual pesticide is subjected to careful and costly toxicological testing prior to its approval. A safety factor (usually 100) is then taken into account to make sure that no undesirable effects occur in humans. In a normal case, therefore, even an exceedance of the maximum quantity cannot be assumed to endanger consumer health. There are only a very few number of active substances that may occur in foods in concentrations that, for example, could lead to temporary malaise (exceeding the acute reference dose). A problem that has not yet been scientifically tackled and is probably still far from being resolved is the existence of several different residue substances and their interactions.
In the European Union, manufacturers and importers are obliged to ensure that the goods they produce or sell comply with the law (self-monitoring). CVUA Stuttgart, as part of the food inspection program in the Federal State of Baden Württemberg, randomly checks whether manufacturers and importers are fulfilling their obligations – "monitoring the self-monitoring". Not all goods can be inspected under the official food control program; that would be far too expensive. On the other hand, we aim to find all pesticide residues that are present in a sample. In other words, our research is not focused on speed, but on a broad spectrum of research and quality. After all, we must be able to present our findings in court, so we cannot allow ourselves any mistakes. Nevertheless, our results are not without effect! If there were no traffic controls, everyone would drive too fast; our work has the same effect. And, since our results are also reported to the EU, monitoring from EU inspectors has been conducted in, e.g. Spain, Italy and Turkey, with problems occurring at the local level also being handled locally. One measure that can be taken is an increased level of controls on the introduction of food and feed from third countries. Without appropriate inspection by an official laboratory such goods can no longer be imported into the EU.
Differences in the use of pesticides result from different climatic conditions and different methods of production. For example, in the Netherlands natural pest control using beneficial insects is often used, which decreases the use of insecticides. Current results of pesticide residues and contaminants in foods of plant origin are continuously published here on our website.
The residue levels in organic foodstuffs differ significantly from conventionally produced foods. In 2017, the average pesticide load on organic fruit and vegetables was 0.002 mg pesticide residues per kg produce. Conventionally produced fruits contained an average of 0.45 mg/kg, and conventionally produced vegetables contained an average of 0.36 mg/kg. That is respectively 225 and 180 times more residues than in organic food. Thus, the impression held by many on different sides that foodstuffs from organic farming and conventional production scarcely differ because of general environmental contamination and cross-contamination or spray drift does not represent the picture for pesticide residues in plant foods.