09
May
Soil Nematodes Vital to Plant Health Threatened by Nontarget Pesticide Exposure, Study Finds
(Beyond Pesticides, May 9, 2025) Research in Advances in Modern Agriculture showcases how pesticide residues can threaten the health of soil nematodes and cause phytotoxic effects in cucumber plants. In assessing both the sprayed vegetables and the organisms within the soil, the authors find a negative correlation between pesticide exposure and soil nematode populations that is proportional to the application rates of the chemicals, as well as alterations in plant development. These impacts highlight potential wider effects on crop productivity, biodiversity, and human health.
“Nematodes, which are microscopic worms inhabiting the soil, are vital contributors to soil vitality and the cycling of nutrients,†the authors share. “Nonetheless, the non-selective and widespread application of pesticides can negatively impact these organisms, leading to potential detriments in soil quality and plant vitality.â€
“Pesticide residues have the propensity to be absorbed and progressively accumulate as they traverse from soil to plants and subsequently to humans,†the researchers state. They continue, “The specific characteristics of the pesticide and its interactions with the body across different levels dictate whether it will be excreted without causing significant harm or if it will accumulate, potentially leading to enduring subclinical and clinical ramifications.†The impacts vary widely between organisms but can become heightened due to bioaccumulation and biomagnification throughout the food web.
Chemical residues cause soil contamination and can threaten the health of the soil microbiome, which is needed for ecosystem stability. As previously reported by Beyond Pesticides, healthy soil contains millions of living species that form the microbiome. 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.
To test those effects, different cucumber plants were exposed to four pesticides: two organochlorine insecticides (Endosulfan and Methoxychlor) and two organophosphate insecticides (Diazinon and Malathion). The study area, within the Teaching and Research Farm at the University of Port Harcourt in Nigeria, consisted of 48 raised beds with three replicates of 16 each. The researchers note that three weeks after germination, the cucumber plants “suffered pest attacks from spotted cucumber beetles, flea beetles, and cabbage loopers.â€
They continue: “To combat this, pesticides such as Diazinon, Endosulfan, Malathion, and Methoxychlor were used, applied in varying concentrations (20 mL, 30 mL, 40 mL) according to a Randomized Complete Block Design (RCBD). Pesticide treatments were replicated three times, with applications made early in the morning weekly.â€
Plant growth metrics, such as leaf height and stem thickness, were collected weekly following the pesticide applications, and at harvest, fruit yield metrics were also recorded. Samples of the cucumbers were taken to analyze the pesticide residues, and nematodes were collected from both the control plots and exposed soil beds for identification and counting.
“The Maximum Residue Limits (MRLs) used for interpreting the pesticide residue levels in this study were based on the Codex Alimentarius international food standards established by the Food and Agriculture Organization (FAO) and the World Health Organization (WHO),†the authors note. As a result of their analysis, they report: “Significant differences in residue levels were found between various pesticides and application rates. Diazinon residues ranged from 0.86 to 2.28 mg/kg, exceeding the MRL of 0.1 mg/kg, indicating soil contamination. Endosulfan had the lowest residues, from 0.44 to 1.75 mg/kg, which were within acceptable limits. Conversely, Malathion and Methoxychlor residues notably surpassed their MRLs, raising potential safety concerns.â€
Through the nematode sampling, the researchers identified the species within the soil at the study site as Meloidogyne incognita. In comparing the nematode populations from the different plots, the authors note “a significant relationship between pesticide concentration and nematode population in the soil,†with the statistical analysis “…indicating a decrease in nematode population with increasing pesticide concentration.â€
They continue, “The slopes suggest that for each unit increase in pesticide concentration, there is a proportional decrease in the nematode population, with Malathion showing the steepest decline, followed closely by Endosulfan, Methoxychlor, and Diazinon.†The data “suggest a strong linear relationship between pesticide concentration and the decline in nematode populations across the range of concentrations studied,†the researchers explain.
Lastly, in examining the pesticide concentrations with the plant development, the study finds potential plant toxicity, or phytotoxicity, specifically with higher concentrations of Methoxychlor and Malathion. The authors note that “some pesticides may exhibit phytotoxic characteristics, which can hinder seed germination, stunt plant growth, and reduce overall crop yields.†(See study here.)
The cucumber is a vegetable with many health advantages, such as promoting hydration, with its high water content, and providing a source of vitamin K, which is essential for blood coagulation and maintaining healthy bones. (See here.) By exposing consumers to levels of pesticide residues above the MRLs, which the study shows across all tested cucumber samples, there is concern for adverse health issues such as “headaches, nausea, rashes, neurotoxicity, cancer, and endocrine dysfunction, which can arise from both direct and indirect exposure to pesticides,†the researchers report. See additional health effects in the Pesticide-Induced Diseases Database.  Â
A previous study of fruit imported into the United Arab Emirates “revealed that most of the imported fruits surpassed the Maximum Residue Limit (MRL) for pesticides, and this underscores a pressing environmental health issue, aligning closely with the outcomes of our investigation,†the authors say. “This trend suggests systemic shortcomings in pesticide management and regulation, raising significant concerns regarding pesticide oversight and application practices in agriculture.†Pesticide residues within food threaten consumer well-being, which necessitates higher food safety standards and enhanced regulation to protect human health.
The resulting soil contamination and threats to nematode populations in the study are also supported by previous research. “El-Marzoky et al. revealed that using abamectin at 500 ppm notably reduced nematode reproduction and gall numbers [growths on plants in the presence of certain nematode species]. This finding parallels the results of our study, where pesticide levels were found to influence soil nematode counts,†the researchers state.
They continue, “Fabiyi et al. also revealed that pesticides, especially at higher concentrations, significantly harm beneficial nematodes and bacteria, which are essential for soil fertility and plant growth.†These findings all showcase the adverse effects of pesticides on nontarget soil organisms, like nematodes, that are essential for soil health and ecosystem functioning.
The authors, in finding that pesticide exposure not only contaminates food and threatens human well-being but can also lead to lower numbers of soil nematodes and has cascading effects on the ecosystem, advocate for a balance between health and sustainable farming practices. “Achieving this balance is essential for future agricultural practices, as it ensures food security while preserving ecological integrity and minimizing potential risks to human health and the environment,†the researchers state.
The organic solution provides exactly that. Studies prove organic agriculture provides soil health benefits, has a significantly lower environmental impact than conventional food production, is more profitable and productive, provides health benefits, and mitigates the crises of climate change and biodiversity. As shared on the Health Benefits of Organic Agriculture page, organic food can feed us and keep us healthy without producing the toxic effects of chemical agriculture.
Learn more about the benefits of organic agriculture here and how to support organic through your diet here and here. Become a member of Beyond Pesticides today to add your voice to the urgent movement of eliminating fossil fuel-based pesticide use within the next 10 years.Â
All unattributed positions and opinions in this piece are those of Beyond Pesticides.
Source:
Imonikebe, P. et al. (2025) Pesticide residue in cucumber-exposed plants, and its associated effects on soil nematode population, Advances in Modern Agriculture. Available at: https://www.researchgate.net/publication/390847748_Pesticide_residue_in_cucumber-exposed_plants_and_its_associated_effects_on_soil_nematode_population.
