Pesticides significantly affect soil life and biodiversity

(Press-News.org) Seventy percent of soils in Europe are contaminated with pesticides. A Europe-wide study co-led by researchers of the University of Zurich now shows that their effects on soil life are substantial, as pesticides suppress various beneficial soil organisms. To protect soil biodiversity, the findings should be taken into account in current pesticide regulations.

Life beneath our feet is essential for maintaining critical ecosystem functions and services like food production, carbon storage, erosion control and water regulation. An international study now provides the first comprehensive quantitative evidence of the prevalence and impact of agricultural pesticides in European soils. According to the results, 70 percent of European soils are contaminated with pesticides. “This contamination has a major impact on various beneficial soil organisms, such as mycorrhizal fungi and nematodes, impairing their biodiversity,” says Marcel van der Heijden, professor at the Department of Plant and Microbial Biology of the University of Zurich (UZH), research group leader at Agroscope, and one of the study leaders.

Soil samples from 26 European countries

The study, published in the renowned Nature journal , was conducted by an international panel of 10 European research institutions including the Joint Research Centre of the European Union, the University of Vigo in Spain, Agroscope and UZH. The researchers investigated the effects of 63 common pesticides on our soils. To this end, they took a total of 373 soil samples from fields, forests and meadows across 26 European countries.

Fungicides, active ingredients against fungi, were the most frequently found. They accounted for 54 percent of all active ingredients. Herbicides followed with 35 percent, and finally insecticides with 11 percent. The most common active ingredient was the herbicide glyphosate. Most pesticides were found in agricultural fields, but the researchers also found pesticides in forests and meadows, where pesticides are not normally applied. This was likely due to spray drift.

Broad-spectrum effects against beneficial soil organisms

The problem of various pesticides is that they not only affect pests that damage our crops but also beneficial soil organisms. The researchers examined the biodiversity of soil organisms, such as bacteria, fungi, nematodes and single-celled organisms, in soil samples. They found that pesticides drastically change living soil communities. “Mycorrhizal fungi, which are important for our crops, are particularly affected by pesticides,” says soil ecologist van der Heijden. Mycorrhizal fungi connect to the roots of crops and help them absorb water and nutrients. The fungicide bixafen, used to combat harmful fungi on cereals, is particularly noteworthy, as it also affects many of the soil organisms studied.

“Some soil organisms, especially various types of bacteria, benefit from the use of pesticides, probably because other organisms are reduced,” adds first author Julia Königer from the University of Vigo. The researchers were able to show that pesticide residues alter soil function. They demonstrated this by testing key genes for soil functions such as the recovery and release of nutrients like phosphorus and nitrogen. “This suggests that the natural function of the affected soil is reduced, and additional fertilization is necessary to maintain yields,” says Marcel van der Heijden.

Adapt current pesticide assessments and regulations

The harmful effects of various pesticides on birds, bees and other insects have long been known and documented. “Our study shows that pesticides represent a very significant human environmental impact on our soils. Often, people don’t even consider the extent of the effects of pesticides on non-target organisms,” says Maria J. I. Briones from the University of Vigo and second study leader. Since some pesticides are difficult to break down, they remain in the soil for years after application and have a major long-term impact on the soil ecosystem.

To protect soil ecosystems, ecotoxicological assessments must move beyond single-species tests to include community-level and functional responses. According to the researchers, these aspects urgently need to be integrated into current pesticide regulation.

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