Agricultural soils are often exposed to more than one chemical at a time, yet environmental risk assessments commonly examine pollutants individually. A new study shows that combined exposure to copper and a commercial glyphosate formulation caused substantially stronger stress responses in earthworms than either contaminant alone. Adding biochar to the soil significantly reduced these behavioral effects, highlighting a potentially practical strategy for managing mixed agricultural pollution.
"Our findings show that contaminant mixtures can create ecological risks that may be underestimated when copper and glyphosate are assessed separately," said senior author Rupesh Kumar Singh of the Universidade de Trás-os-Montes e Alto Douro in Portugal. "Biochar did not completely eliminate the effects, but it clearly improved soil habitability and reduced the earthworms' response to contamination."
Copper is widely used in fungicides, particularly in vineyards, orchards, and horticultural systems. Although it is an essential micronutrient, repeated applications can cause copper to accumulate to toxic concentrations in soil. Glyphosate-based herbicides are also applied extensively in agricultural and nonagricultural environments. Because the two products may be used in the same locations and during overlapping periods, soil organisms can be exposed to both simultaneously.
To investigate this combined risk, the researchers used the earthworm Eisenia fetida, a widely recognized indicator of soil health. Earthworms contribute to decomposition, nutrient cycling, soil aggregation, and aeration, making their behavior an ecologically meaningful measure of whether soil remains suitable for life.
The team conducted a standardized 48-hour avoidance test in which earthworms could move between uncontaminated soil and soil containing different concentrations of copper, glyphosate formulation, or both. Avoidance behavior provides an early warning of chemical stress because earthworms may leave unsuitable soil before exposure causes mortality or reproductive damage.
When tested individually, both contaminants produced clear concentration-dependent responses. Glyphosate treatments caused avoidance rates of approximately 40% to 60%, while copper treatments produced avoidance ranging from 40% to 87%.
The effects became stronger when the contaminants were combined. Earthworm avoidance increased from 60% at the lowest mixture concentration to 100% at the highest concentration, indicating that the contaminated soil had become severely unsuitable as a habitat. Even moderate combined exposure produced a stronger response than the corresponding individual treatments.
The researchers suggest that interactions between copper and glyphosate may alter their mobility, persistence, or biological availability. Glyphosate can bind metal ions such as copper, while elevated copper concentrations may inhibit microorganisms involved in glyphosate degradation. Additives in commercial herbicide formulations may also contribute to toxicity.
To test a possible mitigation strategy, the team added 1% biochar by soil weight, equivalent to an agronomically realistic application rate of approximately 20 metric tons per hectare. The biochar was produced from forestry residues through pyrolysis.
Biochar reduced earthworm avoidance by 29% in one combined treatment and by 27% in the most highly contaminated treatment. Its porous structure and reactive surface groups may immobilize copper and glyphosate, reducing the fraction available to soil organisms.
The researchers emphasize that the experiments used standardized artificial soil to ensure controlled and reproducible conditions. Natural soils contain more complex mineral, organic, and microbial components that may influence contaminant behavior. Field studies, longer exposure periods, and additional measures such as reproduction and biochemical responses will therefore be needed.
Nevertheless, the results demonstrate that earthworm avoidance tests can rapidly detect risks from contaminant mixtures and that biochar may help protect the biological quality of polluted agricultural soils.
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Journal reference: Sousa JR, Matos C, Azevedo T, Gonçalves EN, Rajput VD, et al. 2026. Mitigating the effects of copper and commercial glyphosate formulations with biochar: insights from Eisenia fetida avoidance assays. Biochar X 2: e015 doi: 10.48130/bchax-0026-0013
https://www.maxapress.com/article/doi/10.48130/bchax-0026-0013
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About the Journal:
Biochar X (e-ISSN: 3070-1686) is an open access, online-only journal aims to transcend traditional disciplinary boundaries by providing a multidisciplinary platform for the exchange of cutting-edge research in both fundamental and applied aspects of biochar. The journal is dedicated to supporting the global biochar research community by offering an innovative, efficient, and professional outlet for sharing new findings and perspectives. Its core focus lies in the discovery of novel insights and the development of emerging applications in the rapidly growing field of biochar science.
