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Daily News Blog

01
Apr

Pesticides Are More Widespread in Both Conventional and Organic Agricultural Soils than Previously Thought

(Beyond Pesticides, April 1, 2021) A legacy of toxic pesticide use in agriculture is showing up as residues on organic farms, emphasizing the threat of a history of weak regulatory standards that has left farmland poisoned and the urgent need to transition to organic. A study, published in Environmental Science & Technology, documents the findings of pesticide residues on organic farmland and shows a decrease in residues after transition, with lingering effects for decades.  Some banned pesticides like organochlorines (e.g., DDT and chlordecone) are stable as research demonstrates these chemicals can bind to and linger in the dirt for years to decades. However, other current-use pesticides also pose a soil contamination risk due to drift, runoff, and leaching. 

Widespread, increasing pesticide use in genetically engineered crops has implications for contamination of natural resources, including soils. Since pesticide residues can kill off beneficial soil life, impacting soil health and function, agricultural production may decline. Past studies examining pesticide residues rarely investigate residue’s presence in the soil where the chemical has never been used, like organic systems. Therefore, studies like these highlight the need to examine the effect potential pesticide contamination has on soil health, especially in organic where reliance on biological soil processes is integral to the natural cycling of nutrients for crops. The researchers note, “…[T]he ubiquitous contamination of agricultural soils with a variety of pesticides can have long-term negative effects on soil life. We demonstrate that organically managed sites experience a legacy effect of past conventional management. Moreover, our data indicate that the persistence of both banned and currently used pesticides is underestimated. Even though low concentrations were detected in soils of organically managed fields, the potential effect of this long-term contamination is especially critical, as fields under organic management rely much more on biological soil processes and beneficial soil life such as [arbuscular mycorrhizal fungi] AMF.”

Conventional pesticide use in agriculture and landscaping contaminates soil and their respective compartments. Using synthetic chemicals and fertilizers to sustain crop output and productivity has a detrimental effect on ecosystem health. Although organic agriculture strategies avoid synthetic chemical use, some organic farms manage land with a history of past pesticide use. Therefore, this study aims to compare pesticide quantities and their influence on soil health in conventional and organic farming practices, including land transitioned into organic.

Researchers gathered soil samples from 100 fields in 60 conventionally managed with chemical-intensive practices and 40 organically managed agricultural sites throughout Switzerland. Using the Swiss Soil Monitoring Network, researchers selected 46 modern pesticides to analyze (16 herbicides, eight herbicide transformation products, 17 fungicides, seven insecticides). Researchers measured soil physicochemical properties including, organic carbon, texture, pH, and soil nutrients (nitrogen, potassium, and phosphorus) using the Swiss Federal Agricultural Research Station.

The study finds pesticide residues are present in soils on both conventional and organic agricultural sites. Traditional, chemical-intensive sites have twice as many pesticide residues, and pesticide concentrations are nine times as high as organic sites. Although the amount of synthetic chemical residues decreases significantly with the duration of organic management practices, residues remain in organic soils for decades after the last application. In fields with high levels of pesticides, researchers witness a reduction in microbial abundance and beneficial microorganism concentrations that can have implications for soil health.

Pesticides are pervasive in the environment, affecting all ecosystems, including air, water, soil. Just as clean air and water, healthy soils are integral to ecosystem function, interacting between Earth’s four main spheres (i.e., hydrosphere, biosphere, lithosphere, and atmosphere) to support life. However, soil biology can change due to the presence of synthetic chemical pollutants like pesticides. Studies find some current-use pesticides can induce changes in soil properties that re-release soil-bound chemicals into the ecosystem, contributing to contamination. Past misconceptions assuming stable, banned chemicals like organochlorines, including DDT and chlordecone, would bind to soil and remain immobile are worrisome. A 2020 study finds glyphosate use stimulates soil erosion responsible for soil-based chemical emergence. Continuous pesticide use leaves the dirt bare and more susceptible to decay from lack of organic material, altering the storage compartments of soil sediments from pesticide sinks to sources.

One of the most concerning consequences of soil pesticide contamination is the impact on organisms, including beneficial insects and microbes. Conventional farming technologies promote the use of pesticides that directly and indirectly affect soil organisms.

Many insects are the victims of the global insect apocalypse or population decline. Much research attributes the recent decline to several factors, including pesticide exposureBroad-spectrum pesticides indiscriminately kill pests and nontarget organisms alike, as their ubiquitous use contaminates soils, even in untreated areas. A University of Bern, Switzerland study finds that long-term exposure to sublethal (low-level) concentrations of the neonicotinoid (neonics) insecticides in soil negatively affects the health and behavioral development of black garden ants (Lasius niger) colonies. Furthermore, other studies find pesticides also adversely affect the health of earthworms that provide essential ecosystem services by aerating the soil, cycling nutrients, and increasing microbial activity.

In addition to insects, soil microbiotas are essential for the proper functionality of the soil ecosystem. Microbiotas are ecological communities of pathogenic microorganisms living and working together. Toxic chemicals damage the soil microbiota by decreasing and altering biomass and microbiome composition (diversity). Pesticide use contaminates soil and results in a bacteria-dominant ecosystem as these chemicals cause “vacant ecological niches, so organisms that were rare become abundant and vice versa.”  The bacteria outcompete beneficial fungi, which improves soil productivity and increases carbon sequestration capacity. The resulting soil ecosystem is unhealthy and imbalanced, reducing the natural cycling of nutrients and resilience. Thus, plants grown in such conditions are more vulnerable to parasites and pathogens. The implications of climate change only exacerbate threats to soil health as studies show a link between global climate change and a high loss of microbial organisms in the soil ecosystem.

The unintentional presence of synthetic chemicals in organic agriculture is an all too ever-present phenomenon plaguing organic farmers and gardeners globally. Pesticide runoff, drift, and leaching from nearby conventional agricultural fields can readily contaminate these organic systems. Although implementing trees and shrubbery around organic farms can act as a buffer for pesticide drift, some organic-approved products (e.g., manure and compost) can contain traces of synthetic chemicals. In 2010, organic farmers and gardeners in Washington state experienced severe crop losses throughout the region. Farmers and gardeners suspected that herbicide-contaminated manure and compost from non-organic farms and dairies were responsible. Soil tests and tissue samples from a local dairy manure mixture sent to organic farms found small amounts of aminopyralid, a potent and persistent herbicide. This revelation raised questions about the adequacy of the U.S. Environmental Protection Agency’s (EPA) pesticide registration process. Moreover, contamination from pesticide runoff and leaching can be more difficult to contain as there are various factors to consider, according to the U.S. Department of Agriculture: “intrinsic potential of soils to leach or runoff pesticides, the chemical properties of the pesticides, annual rainfall and its relationship to leaching and runoff, and changes in cropping patterns.”

This study reveals that pesticide residues are present in all agricultural fields regardless of management practices. Previous pesticide use accounts for contamination on some organically managed sites. However, study researchers infer other contamination sources can come from pesticides traveling through the air, water, or soil from nearby conventional fields. Furthermore, this study demonstrates that microorganism biomass and concentrations decrease with increasing soil pesticide residues, especially the abundance of arbuscular mycorrhizal fungi (AMF), a widespread group of beneficial plant symbionts. Therefore, pesticides, in addition to abiotic factors such as pH, negatively impact overall soil health. Researchers suggest future studies examine the synergistic effects pesticide residues and other environmental pollutant sources have on soil health.

Study researchers conclude, “Our work indicates that future studies should not only focus on single pesticides but also consider a wide range of pesticide combinations (e.g., cocktails) and further investigate to what extent these pesticide residues affect soil organisms and consequently soil processes and functions. Additionally, studies should also investigate interactions of pesticide residues with other global change factors such as drought, antibiotics, or microplastic since these abiotic and anthropogenic stressors can synergistically or antagonistically affect soil microbiota and reduce soil functioning.”

Healthy soils are essential in maintaining normal ecosystem function and interaction, even outside of the soil environment. Chronic, low-level exposure to pesticide residue in soil habitats weakens soil health and productivity and has implications for soil-dwelling organisms. Organic production standards must be strengthened in addressing problems associated with soil contaminants in order to protect soil health and productivity. By protecting soil health from contamination, you keep agriculture safe for food commodities and safeguarding human, animal, and environmental health. The National Organic Standards Board must bring greater attention to the damage that contaminants associated with widespread pesticide use adversely affect the overall soil health for future generations as well as off-target movement of chemicals that degrade soil on an ongoing basis. This necessarily goes beyond the current focus on residues in the finished food commodities.

Solutions like buyinggrowing, and supporting organic can help eliminate the extensive use of pesticides in the environment. Organic land management eliminates the need for toxic agricultural pesticides. Furthermore, regenerative organic agriculture nurtures soil health through organic carbon sequestration while preventing pests and generating a higher return than chemical-intensive agriculture. Moreover, supporting the use of alternative practices such as polyculture rather than monoculture, mulching around the base of the plant, animal integration, and other organic practices can assist in eliminating the need for pesticides and the likelihood of pesticide drift. Learn more about the adverse health and environmental effects chemical-intensive farming poses for various crops and how eating organic products reduces pesticide exposure.

For more information about organic food production, visit Beyond Pesticides’ Keep Organic Strong webpage.

For more information on how organic is the right choice for both consumers and the farmers who grow our food, see Beyond Pesticides webpage, Health Benefits of Organic Agriculture

Sources: Environmental Science & Technology, EurekAlert! Science News

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