Synergistic Effects from Glyphosate and Urea Fertilizer Magnify Earthworm Poisoning
(Beyond Pesticides, November 4, 2025) A study of earthworms published in Environmental Science & Technology highlights how chemical mixtures can have both synergistic and species-specific effects, threatening the soil microbiome and overall soil health. In exposing two species, Eisenia fetida and Metaphire guillelmi, to the weed killer glyphosate alone and in combination with urea, a form of synthetic nitrogen fertilizer, the researchers find enhanced toxicity with co-exposure as well as varying health effects between the two species. These results emphasize the need to test a wide variety of nontarget organisms for impacts from environmental contaminants, since species, even within the same genus or family, can exhibit vastly different effects.
Glyphosate, as one of the most widely used herbicides worldwide, is highly researched, with a multitude of studies linking the weed killer to effects on humans, wildlife, and soil ecosystems. Since simultaneous application of glyphosate and urea frequently occurs in agriculture, the effects of this mixture on earthworms are crucial for understanding the overall impacts on soil health. In exposing the two species to the individual compounds and as a mixture, the authors report increased glyphosate residues in earthworm gut contents, reduced body weight, aggravated intestinal tissue damage, sharply decreased digestive enzyme activity, and intensified gut microbiota dysbiosis, among other health effects.
In highlighting the species-specific impacts, the researchers state, “Besides these same impacts, E. fetida exhibited more severe oxidative damage and energy metabolic disorders under co-exposure, while M. guillelmi showed greater sensitivity in intestinal tissue and microbial responses.” These results, in simulating the widespread co-exposure of glyphosate and urea in agricultural soils, shows the “markedly intensified glyphosate-induced growth inhibition and intestinal toxicity in earthworms.”
The authors continue, saying: “Co-exposure facilitated the accumulation of glyphosate in earthworm gut contents, triggering a cascade of more severe intestinal damage, immune activation, and gut microbiota destabilization… [O]ur results highlight the underappreciated risks of such combined exposures for key soil fauna that regulate nutrient cycling and soil structure.”