04
Nov
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.â€
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.â€
Study Importance
As Beyond Pesticides has previously reported, healthy soil contains millions of living species that form microbiomes. Most of the biodiversity in soil consists of bacteria and fungi, and their number and type are regulated partially by predatory protists and nematodes that feed on bacteria. In working together, these tiny organisms determine the health of the soil for plant growth. The soil microbial community is an important indicator of soil health, and pesticide residues in the soil can change its structure and promote resistance in some microorganisms. The soil microbiome requires balance, and contamination from toxic chemicals can affect the stability of the soil ecosystem with cascading impacts, ultimately, to human health. (See Daily News here, here, and here.)
Recent research published last month links pesticides, antibiotics, and nitrogen fertilizers to the extreme global crisis of antibiotic resistance, raising serious concerns about the adverse impacts of conventional (chemical-intensive) agricultural practices. In a particularly novel and significant finding, the researchers found that nitrogen is a strong driver of resistance processes. The influence of nitrogen fertilizers adds an important dimension to the role of agricultural practices in generating antibiotic resistance. Nitrogen benefits some soil microbes, but it is a stressor for many others. It increases antibiotic-resistance gene (ARG) abundance and can enhance uptake of the heavy metals cadmium and copper by crops. Other effects include reducing enzyme activity and acidifying the soil. (See Daily News here.)
For the current study, two earthworm species are analyzed. As the authors point out, earthworms play critical roles in various key soil ecological processes, with a wide body of science showing the toxic effects of glyphosate on earthworms. “[A]n increasing number of studies have emphasized that both short-term and long-term exposure to glyphosate can reduce earthworm survival, decrease biomass, suppress reproduction, and induce oxidative damage and reproductive impairment,†the researchers state. They continue, “These findings highlight the potential toxic effects of glyphosate on earthworms, which may further impair their ecological functions within soil systems.â€
Urea is one of the most widely used nitrogen fertilizers and is often used in conjunction with glyphosate in agricultural soils. The authors note, “Urea can change soil pH, nitrogen forms, and microbial communities, thereby influencing glyphosate adsorption, degradation, and persistence.†(See research here and here.) Since fertilizers are often applied alongside pesticides, understanding how these mixtures interact and impact soil health is imperative.
Methodology/Results
In the study, E. fetida and M. guillelmi were exposed to soils treated with environmentally relevant concentrations of glyphosate, urea, or a combination of both for 28 days. After which, the “concentrations of glyphosate and its metabolite aminomethylphosphonic acid (AMPA) in both soil and gut contents were quantified, gut microbiota via 16S rRNA sequencing was characterized, and toxicological effects, including growth inhibition, intestinal barrier histopathology, and oxidative and energetic imbalance, were evaluated.â€
The researchers find:
- Co-exposure with glyphosate and urea increases glyphosate residues in earthworm gut contents by 9.89−40.23% and reduces the body weight of the earthworm by 17.86−21.05%.
- “At 10 mg/kg glyphosate, urea co-application markedly increased glyphosate residues in soil and earthworm gut contents, potentially aggravating glyphosate toxicity to earthworms.â€
- In comparison, the guillelmi treatment group exhibits generally higher glyphosate residues in both soil and intestinal contents than E. fetida.
- Co-exposure also “aggravate[s] intestinal tissue damage, sharply decreased digestive enzyme activity, upregulated lysozyme [an enzyme that plays a crucial role in the immune system] expression by more than 150.28%, and raised LPS content [lipopolysaccharide; linked to gut dysbiosis] by over 10.08%.â€
- Gut microbiota dysbiosis is intensified, with the bacteria inflammatory marker phylum Proteobacteria increasing by 6.98−17.52%.
- The body length and weight of the earthworms decreased after 28 days of exposure, with co-exposure causing the largest weight loss.
- “M. guillelmi is more sensitive to the combined effects of glyphosate and urea than fetida, exhibiting a more pronounced growth inhibition.â€
- Co-exposure with urea further aggravated tissue damage in both earthworm species when compared with glyphosate alone, “causing intestinal wall thinning, hemocoel congestion, and increased epidermal muscle congestion.â€
- “M. guillelmi exhibited more severe intestinal damage, particularly degeneration and loss of chloragogenous tissue†than fetida.
- Urea co-exposure also aggravates mitochondrial dysfunction under glyphosate stress, disrupts antioxidant defenses and energy metabolism more severely, and “alters the effect of glyphosate on the gut microbiota composition in both earthworm species, with a more pronounced differentiation observed in fetida.â€
The species-specific results highlight the importance of studying a wide range of nontarget organisms. As the authors summarize: “The sensitivity and key damaging mechanisms differed between the two earthworms: oxidative damage was predominant in E. fetida, whereas gut barrier disruption and gut microbiota alterations were more critical for M. guillelmi. Our findings highlight that urea co-exposure amplifies glyphosate toxicity risks in earthworms and underscore the necessity of considering the differential responses of earthworm ecological types in future soil ecological risk assessments.†(See Beyond Pesticides’ coverage on the deficiencies of risk assessments and regulatory failures here, here, and here.)
Previous Research
Included in the current study, the authors cite a wide body of science on not only the effects of glyphosate and other pesticides on health and the environment, but also particularly for synergy and impacts on soil organisms. This research includes:
- The extensive use of glyphosate is linked to effects on nontarget soil organisms, with the risks to soil ecosystems widely studied. (See here, here, here, here, and here.)
- One study shows that frequent application in tropical systems of glyphosate “reduced soil macroarthropod richness by 21% and altered community composition.
- “A recent global risk assessment of glyphosate further estimated that 67−93% of soils pose high risks to Collembola [springtails] and 43−67% pose medium to high risks to earthworms.†(See here.)
- Studies show that glyphosate combined with microplastics causes notable synergistic effects. (See research here and here.)
- “Co-exposure to polyethylene microplastics and glyphosate aggravates neuro-behavioral disorders, intestinal barrier injury, and gut microbiota imbalance.†(See here.)
- One study shows that urea co-exposure increases glyphosate and AMPA residues in soil.
- “[C]ommercial glyphosate-based herbicides (GBHs) contain surfactants, such as polyethoxylated tallow amines, which have been shown to amplify the risks associated with glyphosate.†(See here.)
- Studies show guillelmi exhibits greater toxicity and ecological sensitivity than the E. fetida with organophosphate pesticide exposure.
- “[C]ombined exposure to imidacloprid and PLA [polylactic acid] microplastics, fluindapyr and microplastics, or tebuconazole and polyethylene microplastics causes more severe epidermal and intestinal damage and heightened immune responses. Damage to the epidermis and intestinal wall, the main barriers against contaminants, is closely linked to digestive disorders and impaired immunity in earthworms.†(See studies here, here, here, and here.)
The Alternative: Organic Land Management
To protect soil health and ensure a balanced soil microbiome, a holistic solution is available. This involves eliminating the use of petrochemical pesticides, including glyphosate, and synthetic fertilizers that contain urea, and adopting organic methods. Countless studies confirm the soil health benefits of organic agriculture, as it can improve ecological functions damaged by chemical-intensive farming practices. (See a small subsample of research here and here.) Beyond Pesticides advocates for organic land care in all areas, including agriculture, public parks and places, as well as residential areas.
Additional information, shared in Daily News entitled Organic Farming Competes with Chemical-Intensive Practices on Resilience, Input Costs, and Profitability, highlights the multifaceted benefits of organic. Visit Products Compatible with Organic Landscape Management and Fertilizers Compatible with Organic Landscape Management, as well as Cost Comparison: Organic vs. Chemical Land Management, for more information on transitioning to organic practices.
By focusing on a healthy system that starts with the soil, the use of petrochemical pesticides and fertilizers becomes obsolete. To learn more about the health and environmental benefits of organic land management, see here and here. Help support Beyond Pesticides’ mission by becoming a Parks Advocate with the Parks for a Sustainable Future program, becoming a member, or making a gift contribution today.
All unattributed positions and opinions in this piece are those of Beyond Pesticides.
Source:
Li, P. et al. (2025) Urea Co-exposure Increases Glyphosate Toxicity in Earthworms: Evidence from Species with Distinct Sensitivities, Environmental Science & Technology. Available at: https://pubs.acs.org/doi/abs/10.1021/acs.est.5c10842.
