Some combinations of currently used pesticides are toxic to soil organisms. Scientists are now preparing tools to predict their occurence in the environment.

Since 2020, the RECETOX center has been involved in the European project SPRINT. This five-year project aims not only to measure new data on the occurrence and effects of pesticides in the environment but also to develop tools that will allow their impacts on the environment and human health to be modeled and predicted. The project is now nearing its end and brings important outputs at the level of knowledge and tools.

27 Jan 2025 Sabina Vojtěchová Article Research

In 2021, Professor Hofman's team collected hundreds of different types of samples across the Czech Republic to analyze residues of more than 200 pesticide substances. Similarly extensive campaigns were also conducted in 9 other European countries.

The focus of the project is very broad and includes several work packages aimed at specific goals related to pesticide research. One of them, for example, focused on extensive soil sampling in ten European countries and Argentina, based on which the occurrence of pesticide substances was determined.

“The sampling took place as a one-time event in 2021, but it took several years to analyze all the samples and process the data. For the Czech Republic alone, the sampling of all types of samples represented 30 full days in the field. A summary publication has now been released, and separate articles are being published for each matrix, such as soil, crops, or human blood,” explains Professor Jakub Hofman from the RECETOX center, who is involved in the project, coordinates one of the work packages, and leads the project team at Masaryk University. According to Hofman, the results have shown that mixtures of current and historical pesticides represent a significant and serious burden on the environment and the human body.

Apart from the 2021 study, the project also includes other activities, such as the development of new models for the occurrence and behavior of pesticides in the environment or testing the effects of pesticide mixtures on various types of organisms. The RECETOX center was very intensively involved in this part of the project.

“As part of the SPRINT project, the impacts of pesticide mixtures on human health were studied, including toxicological studies and the analysis of epidemiological data. Our group specifically participated in ecotoxicology, i.e., studying the impacts of pesticide mixtures on organisms in the environment. We tested the effects of real mixtures found in samples from 2021 on soil organisms such as earthworms, springtails, plants, and microorganisms. We collaborated with the University of Hohenheim in Germany and Wageningen University in the Netherlands. This part of the project has also been completed, and publications are now being prepared. The most alarming finding is that pesticide mixtures affect the reproduction of organisms, microbial parameters, or plant growth even at concentrations commonly found in agricultural soils, which were considered safe when the substances were approved,” explains Hofman.

The main problem with pesticide mixtures is that the legislative process assesses each substance individually or only considers the combination of substances that are together in a commercial product. In the real environment, however, complex mixtures of various pesticides are formed and persist after application. Their cumulative effect on organisms is thus completely different and much more serious.

“In agricultural soil, we can find ten, sometimes even twenty substances in one place at one time. According to the approval, their individual concentrations should be safe, but the cumulative effect in practice causes, for example, strong inhibition of earthworm or springtail reproduction. When we calculated the risk for pesticide mixtures found in Czech fields, it turned out that for a third of them, earthworms would not reproduce in the soil. Earthworms contribute to soil aeration, their presence affects the water and air regime, and they also support the functioning of microorganisms. Therefore, they should definitely not be missing in healthy agricultural soil,” explains Hofman.

The effect and toxicity of currently used pesticides do not accumulate only in place but also over time. About a quarter of the currently used pesticides can be considered relatively persistent substances. Such a substance takes a hundred or more days (which corresponds to a third of a year or an entire agricultural season) to degrade to half of its original concentration. A significant proportion of pesticides thus remain in the soil for up to a year, and their concentrations are still detectable and measurable after two years. Moreover, pesticide applications to the soil usually occur more than once a year.

“The farmer goes out into the field two or three times, applying various substances such as herbicides, fungicides, and insecticides. All of this mixes together and stays for about a year, sometimes even until the next season. Then the farmer comes again, applies something else, and thus creates a colorful cocktail of substances,” explains Hofman.

The fate of substances and their mixtures in soils is very difficult to generalize. Each behaves a bit differently in the environment due to its unique properties. Some degrade quickly, but the resulting product is more mobile in the environment. Substances can thus continue to leach into groundwater. Sometimes it also happens that the resulting product is just as toxic or even more toxic than the original pesticide.

“The resulting products of pesticide degradation are generally a very broad and unexplored topic that is certainly worth further research. For example, glyphosate is strongly suspected of being carcinogenic to humans, but it is used with the argument that its degradation occurs within days, so the likelihood of a person near the field receiving a significant dose is very small. However, AMPA, which is a degradation product of glyphosate, has enormous persistence and remains in the field for months, sometimes even years. It is a substance toxic to microorganisms and plants, and we do not yet know whether it is also dangerous to humans,” says Hofman.

The diverse fate of pesticide substances and mixtures does not escape organic farming either. Again, it is necessary to keep in mind that substances migrate between environments. The results of another study, in which RECETOX collaborated with Mendel University in the past, showed that plants in organic farming contain significantly fewer pesticide residues and significantly lower concentrations, but even here protection is not one hundred percent.

"In organic farming, there is a three-year period during which synthetic pesticides must not be applied to the field. However, this period may not be sufficient for the degradation and leaching of all present substances. Another way pesticides enter organic farming is through the already mentioned mobility of substances between environments, in this case, transfer between neighboring fields, where drift occurs during application in conventional farming.

In the Czech landscape, it is rarely the case that organic farming is somehow distance-isolated from conventional farming; fields usually alternate, and conventional is right next to organic. This way, transfers occur," adds Hofman

SPRINT is also trying to respond to the issue of the currently unpredictable effects of mixtures of applied substances in its activities. Tools that work based on data generated by the mentioned process of approving plant protection products could help with the evaluation. National pesticide registries and consumption statistics, which contain a wealth of valuable information, are created during this process. Scientists are now creating a model from these data that will allow predicting the inputs of used substances into the environment and their subsequent transport and occurrence of their mixtures in soil, water, and air. By linking to toxicological databases, they want to predict the resulting effects and risks for organisms. A great advantage of the model is its use on a large scale.

“Unlike soil sampling, which usually includes only very small amounts of data, pesticide use databases and national product registries are enormous. Therefore, scientists are now trying to figure out how to take this existing data from legislation or consumption statistics and use it to model and predict the amounts and types of substances that reach the fields,” explains Hofman.

Processing the data will result in, for example, a map of the Czech Republic that should include every field with modeled inputs of specific substances in a specific year. From the map, it should be possible to read how much of the substances remain in the soil, how much reaches surface waters, how much reaches the air, and what risk the mixtures might pose to soil or water organisms.

“Such a map would have enormous potential for decision-makers because it will be possible to identify zones in advance and plan the cultivation of specific crops to minimize risk. Europe has an ambitious plan within the ‘Farm to Fork’ strategy to reduce overall pesticide use by 50% and overall risk by 50% by 2030. The map could help manage this risk,” says Hofman.

The SPRINT project was initially a response to a European challenge following the Farm to Fork strategy. The strategy is a key part of the European Green Deal, which aims to create a sustainable, fair, healthy, and environmentally friendly food system. Finding tools to help Europe prioritize substances and decide which to eliminate and which to keep was the task set by the European Union. SPRINT is now in a monitoring period, and a meeting with the European Food Safety Authority (EFSA) commission recently took place where the tool was presented. Whether it will be used is now in the hands of EFSA. The strategy is not binding, and the only legislative measures that exist date back to 2009.

“We have the European Directive on the Sustainable Use of Pesticides, which requires the use of fewer pesticides and more prudent management. However, the definition of risk used by the directive does not correspond to current scientific knowledge; it is more about creating very broad categories of substances whose risk is estimated and not based on actual toxicological data. Last year, a new Sustainable Use Regulation was on the table, but it was rejected. So, we have a strategy with very ambitious goals, but we do not have the hard legislation to ensure that the goals are achieved,” explains Hofman.

The problem is not only the lack of legislation. At the European level, there is also a lack of an independent advisory service that farmers could turn to. “We would need an authority that could recommend suitable substances regardless of what distributors promote. There is the Plant Health Portal, but it is based on data generated during registration, so it does not contain any data related to the so-called post-registration phase, i.e., how substances actually behave in the environment after application,” adds Hofman.

Scientific studies show that the need for better understanding of pesticides and more prudent management of them is more than current. If the current way of farming does not change in the long term, according to Professor Hofman, the soil will gradually die.

“I will return to the mentioned glyphosate. It attacks the metabolic pathway that not only plants, i.e., weeds, for which glyphosate is intended, have, but also bacteria, for which it is highly toxic. However, bacteria play an absolutely crucial role in the soil, so glyphosate actually kills the soil. Fungicides are used against plant fungal diseases, but not every fungus in the soil is harmful; on the contrary, arbuscular mycorrhiza is very important for many plants, and fungi contribute to soil health, yet fungicides also kill these important microorganisms. Everything is very interconnected,” summarizes Hofman.

The image shows how often mixtures of pesticide substances were found in soils in fields and in what quantities. Although it was clearly proven that organic farming soils had lower pesticide loads, even these soils were not completely free of pesticides. The sad result is that Czech soil samples showed the worst results (up to 21 simultaneously detected substances) and also the highest total concentrations of pesticides (see the next image).
A comparison of the total concentration of pesticide substances in soil samples from different countries and in conventional and organic farming. The box plot summarizes the results from individual fields (usually 10 conventional and 10 organic for each country): the box represents 25% to 75% of all values, and the line in the box is the median of all values. The T whiskers show the minimum and maximum values without outliers. Note that the Y-axis is logarithmic.

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