Pesticide residues persist in soils across France

2023-06-12 09:30:33

Following soil analyzes carried out at nearly fifty sites throughout France, scientists have revealed that pesticide residues persist in the soil, well beyond their theoretical degradation time. Even forests, meadows and wastelands are affected by this contamination.

The use of pesticides is the basis of modern agriculture, with more than 2.7 million tonnes of active substances used worldwide in 2020, an increase of 50% since the 1990s. In Europe, France is the leading consumer country and this intensive use raises concerns regarding their future in the environment and the resulting impacts on ecosystems. Although pesticides are closely monitored in water, this is not the case in soils. INRAE ​​researchers, with the collaboration of the University of Bordeaux, carried out soil analyzes throughout mainland France. Their work has just been published in the journal Environmental Science & Technology.

A total of 47 sites from the Soil Quality Measurement Network (RMQS), a national soil change observation program, were sampled between 2019 and 2021, at a depth of 0-20 cm. These are mainly cultivated soils (field crops, vineyards and orchards), but also supposedly untreated soils, such as meadows, forests and wasteland. The scientists researched 111 substances, which were prioritized by ANSES on the basis of their uses and their behavior in the environment.

The analyzes showed a generalized presence of pesticides in almost all the soils, since 46 of the 47 sites, or 98%, contain at least one substance in the topsoil. And 67 different substances were detected; fungicides being the most frequent with a detection rate of 69%, followed by herbicides (61%) and insecticides (40%). The most frequently detected molecules are glyphosate and AMPA (aminomethylphosphonic acid), its main metabolite, which are present in respectively 70% and 83% of the soil samples taken. The researchers observed that the persistence of these pesticide molecules goes well beyond their theoretical degradation time and at higher than expected concentrations.

The understanding of soil contamination is still poorly understood

The number of pesticide residues quantified per site varies from 1 to 33, with a median value of 9 substances. Cultivated soils are unsurprisingly the most contaminated, with a median of 15 pesticide residues detected, and almost all of these soils contain at least seven residues. The most unexpected of the results is the detection of more than 32 different pesticides in soils under forests, permanent grasslands, fallow land or organic farming for several years, admittedly with concentration levels that are mostly lower than for arable sites.

The major contamination hypothesis for these uncultivated lands might be the proximity to treated fields. For example, two forests studied are located near arable land and the most contaminated industrial wasteland is near a vineyard. Nevertheless, two other forests are surrounded by grassland and forest, suggesting other factors influencing soil contamination, such as long-range atmospheric transfer induced by unfavorable atmospheric conditions.

The scientists also assessed the consequences of the presence of these pesticide molecules on soil organisms. According to them, the risk is not negligible on many sites, but six present a high risk and concern arable land cultivated in conventional agriculture. Regarding uncultivated land (grassland, forest and wasteland), most soils presented a negligible or low risk for earthworms.

“The widespread presence of pesticide residues in almost all sampled soils, including organic fields and untreated areas such as forests and permanent grasslands, highlights the lack of knowledge regarding the dispersion of pesticides in the environment. », note the authors of this study. They add that: “The results argue for the integration of pesticide residues into soil monitoring at the national level and a revision of the procedures for registering the use of pesticides in real agricultural practices. Moreover, these substances should be taken into account in the construction of future regulations on soil protection and in particular the European law on soil health currently under discussion. »

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