13
May
Adding to Wide Body of Science, Study Finds Pesticide Residues Threaten Health of Soil Microbiome
(Beyond Pesticides, May 13, 2025) A study in Environmental Pollution examines ecological and health risks in farmland soil with pesticide contamination. “Although agricultural soil pesticide residues have long threatened the environment, a relatively complete system for evaluating their health and ecological risks has not yet been developed,†the authors state. In addressing this research gap, the study finds that “more than ten pesticides were detected in 98.62% of the soil samples, which changed the soil environment†and threatens the health of the soil microbiome.
The authors continue, “This study investigated the correlation between pesticide residue risks and soil ecological security and human health, revealed the response characteristics of soil microbial communities under pesticide stress, and identified microbes strongly related to pesticide ecological risks.†Pesticides, as the authors emphasize, “inevitably pollute agricultural soil, affect the ecological environment, and pose a threat to human health.†(See studies here, here, and here.) With this in mind, they assess 50 selected pesticides in 145 soil samples from agricultural land in Zhejiang Province, China and calculate the associated risks to ecosystems and public health.
In describing the importance of this research, the authors explain: “Pesticides are prone to leakage and drift in environmental media, turning from point sources to non-point source pollution, thereby further deteriorating the environment and posing a serious threat to soil ecology. The soil microbial community is an important indicator of soil health, however, pesticide residues in the soil can change its structure and promote resistance in some microorganisms.†(See Daily News here and studies here, here, and here.)
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 here, here, here, and here.) These impacts, however, are complex and difficult to identify, as there are a variety of pesticides and their mixtures in agricultural soils.
Study Methodology
The 145 soil samples were obtained from citrus orchards (26), vineyards (29), and vegetable gardens (90) and range in crop types, 48 of which were from leafy vegetables, 4 from brassicas, 9 from solanaceous vegetables, 6 from legumes, 2 from melons, 10 from bulbs, and 11 from root vegetables. Each sample was analyzed for pesticide residues and physicochemical properties such as total nitrogen, pH, and organic matter.
From the data, ecological and health risk evaluations were performed. “A health risk evaluation was conducted to more comprehensively evaluate the health effects of pesticide residues in agricultural soils on human health,†the researchers state, with parameters for the model based on U.S. Environmental Protection Agency (EPA) standards and relevant literature.
“The soil ecological risks caused by pesticide residues are complex and have different degrees of impact on soil animals, plants, and microorganisms,†the authors share. (See studies here, here, and here.) They continue: “No assessment method can simultaneously reflect the response of each niche to pesticide residues. However, to more comprehensively assess the contamination levels of pesticide residues in samples, it is necessary to calculate and quantify the risks posed by pesticides in soils.â€
In using ecotoxicology data from earthworms, the researchers calculate ecological risk of each of the 50 selected pesticides to assess the ecological risk of pesticides in soil samples from each agricultural area. “Earthworms are ecosystem engineers who can affect soil fertility, promote crop growth, and improve the soil environment,†the authors note.
Results
As an outcome of testing all soil samples for pesticide residues, the researchers find that, of the 50 pesticides included in the analyses, “more than 10 pesticides were detected in 98.62% of the soil samples, and more than 20 pesticides were detected in 56.55% of the soil samples. A further detailed analysis of the detection rates of specific pesticide types in the samples revealed that 33 pesticides were detected in 20% of the soil samples, and 17 pesticides were detected in 60% of the soil samples.â€
Notably, up to 20 types of pesticides were found in soil with nightshade vegetables. A previous study supports this, as it found “that the concentration of residual pesticides in the soil of nightshade lands was greater than that in the soil of other crops.†Additional results show that soil properties, including pH and total nitrogen, experience negative inhibitory effects with pesticide residues, which “highlights the potential associations between pesticides and soil physicochemical properties.â€
From the health risk assessment, the calculations identify high carcinogenic risks from dimethomorph, imidophos, indoxacarb, and imidacloprid. Interestingly, the authors share, “We further evaluated the difference in the risk posed by different planting behaviors and reported that the soil with the highest average cancer risk was that planted with nightshades.â€
Within the ecological risk assessment, nightshade vegetables were the planting type with the highest average, and the insecticides chlorpyrifos and bifenthrin were identified as having higher entropy (uncertainty) values, classifying them as ‘medium ecological risk threats.’
From the extraction and sequencing of soil microbial DNA, the researchers classified “taxonomic groups of 62 phyla, 201 classes, 543 orders, 949 families, 2,514 genera, and 7,215 species of microbes†from the samples. They note: “The vineyard soil had the most unique species (1,059) among all planting types. As the type with the most serious pesticide residue pollution and highest ecological risk, nightshade land had only 52 exclusive species.â€
The soil microbial communities were most impacted by dimorpholine, and the “soil bacterial composition changed significantly under different ecological risk levels at the phylum level [the third broadest level of taxonomic classification of biological communities].†Of the bacteria, Firmicutes exhibit the clearest response to pesticide residues. “With the increasing ecological risk, the relative abundance of Firmicutes gradually decreased,†the authors say. “Specifically, the relative abundances were 8.76, 7.04, and 0.98% at negligible, low, and medium ecological risk levels, respectively.â€
Altering the abundance of Firmicutes, and any soil biota, leads to impacts on soil health and crop productivity. A study in Science of The Total Environment similarly reported that with increasing concentrations of the insecticide chlorantraniliprole that the proportion of Firmicutes in the soil decreased. In the present study, the significant decrease of the relative abundance of Firmicutes, with an increase in the ecological risk of pesticide residues, suggests that these bacteria may be an indicator of the ecological risk of pesticides.
This group of bacteria plays an important role in soil ecosystems. Firmicutes contribute to the decomposition of organic matter and nutrient cycling, as well as promote plant growth and suppress diseases. They are also active in chitin degradation and can provide substrates for iron reducers. (See study here.)
“In summary, our study investigated the characteristics of pesticide residues in an actual agricultural environment and their risk-related relationships with soil ecological security and human health, [and] revealed the response characteristics of soil microbial communities under pesticide stress,†the researchers conclude.
Previous Research
As the study points out, the “problem of pesticide residues in soil has a long history.†With the ubiquitous contamination of multiple pesticide residues in agricultural soils worldwide, a multitude of studies identify various impacts, including synergistic effects, to biodiversity, ecosystem functioning, and human health, as a result.
“Several studies have concluded that humans, as the most direct users of pesticides and those who come into contact with them, are exposed to both carcinogenic and non-carcinogenic risks from pesticides,†the authors note. (See here and here.) “Certain pesticide ingredients may increase the risk of cancer development with long-term exposure as well as a range of non-carcinogenic risks, such as neurotoxicity and endocrine disruption, which pose potential threats to human health.†Disproportionate risk to farmworkers, their children, and those who live near agricultural land is also well documented. (See here.)
In recent coverage of research in Advances in Modern Agriculture, the threats to soil nematodes from pesticide residues, as well as the resulting phytotoxic effects to cucumber plants with exposure, are highlighted. The authors, in assessing both the sprayed vegetables and the organisms in the soil, find a correlation between pesticide exposure and adverse effects on 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.
Additional Daily News highlights various studies that identify the significance of organic farming systems in advancing soil health in comparison to chemical-intensive agriculture. As previously covered, in 2022, the Rodale Institute released the findings of its forty-year-long comparative analysis of organic and conventional grain production, finding that:
- Organic systems achieve 3-6 times the profit of conventional farms.
- Yields for the organic approach are competitive with those of conventional systems after a five-year transition period.
- Organic yields during stressful drought periods are 40% higher than conventional fields.
- Organic systems leach no toxic compounds into nearby waterways.
- Organic systems use 45% less energy than conventional farming systems.
- Organic systems emit 40% less carbon into the atmosphere.
Countless other studies (see here and here) confirm the soil health benefits of organic agriculture, as it can improve ecological functions damaged by chemical-intensive farming practices. By focusing on a healthy system that starts with the soil, the use of petrochemical pesticides and synthetic fertilizers becomes obsolete.
To learn more about the benefits of organic land management, see here and here. Become an advocate for organic parks by engaging with your community leaders and advertising your commitment to pesticide-free spaces with “Pesticide Free Zone†signs. Help support Beyond Pesticides’ mission by becoming a member or making a gift contribution today.
All unattributed positions and opinions in this piece are those of Beyond Pesticides.
Source:
Tang, T. et al. (2025) Systematic assessments of ecological and health risks of soil pesticide residues, Environmental Pollution. Available at: https://www.sciencedirect.com/science/article/abs/pii/S0269749125007213.
