Tiny fragments of plastic waste are changing how soil bacteria and fungi break down organic matter, a shift that could undermine the ability of agricultural land to trap carbon dioxide and maintain fertility, according to new research from laboratories in Europe and North America.
The findings add to mounting evidence that microplastics, which have been detected in nearly every environment on Earth, are not inert pollutants but active agents that interfere with biological processes. Scientists now worry that widespread contamination of farmland could accelerate climate change by disrupting the microbial communities that help soils act as carbon sinks, storing roughly three times more carbon than the atmosphere.
Researchers at institutions including the University of Zurich and the University of Massachusetts have documented specific mechanisms by which plastic particles smaller than five millimeters alter microbial metabolism, reproduction rates, and the production of enzymes that decompose plant material. The disruptions appear to reduce the efficiency with which microbes convert dead vegetation into stable soil carbon, potentially releasing more greenhouse gases into the atmosphere.
Plastic Particles Disrupt Enzyme Production in Decomposer Communities
A study published in Environmental Science and Technology by researchers at the University of Zurich examined how polyethylene and polystyrene fragments affect the soil fungus Aspergillus niger, a key decomposer of plant material. The team exposed fungal cultures to microplastic concentrations similar to those found in agricultural soils near urban areas, ranging from 0.2 to 2 percent by weight.
Within 72 hours, the fungi showed a 34 percent reduction in the production of cellulase, an enzyme essential for breaking down cellulose in plant cell walls. Production of lignin peroxidase, which degrades the tough lignin that gives plants structural support, dropped by 41 percent. Both enzymes are critical for converting crop residues and other organic matter into humus, the stable form of carbon that can remain in soil for centuries.
The researchers found that microplastics adhered to fungal hyphae, the thread-like structures fungi use to explore soil and secrete enzymes. Electron microscopy revealed that plastic particles created a physical barrier on hyphal surfaces, reducing the area available for enzyme secretion. Chemical analysis showed that additives leaching from the plastics, including phthalates used as plasticizers, interfered with the cellular signaling pathways that regulate enzyme production.
"The fungi were still alive and growing, but their ability to perform their ecological function was significantly impaired," said Dr. Michael Weber, a soil ecologist who led the study. "They were essentially working with one hand tied behind their back."
The team also tested the fungi's ability to decompose actual plant material, mixing sterilized wheat straw with soil containing microplastics. After six months, soils with 2 percent microplastic content showed 28 percent less decomposition than control soils. The undecomposed plant material contained carbon that would normally have been processed into stable soil organic matter or released as carbon dioxide through normal microbial respiration. Instead, it remained in a form vulnerable to rapid decomposition if conditions changed, representing a potential source of future emissions.
Bacterial Communities Show Altered Carbon Processing Under Plastic Exposure
Complementary research at the University of Massachusetts Amherst focused on bacterial communities, which handle different aspects of decomposition than fungi. A team led by soil microbiologist Dr. Jessica Gutknecht collected soil samples from 15 agricultural fields across New England and measured baseline microplastic concentrations, which ranged from 0.3 to 4.2 particles per gram of soil. The team then tracked microbial activity over two growing seasons.
Fields with higher microplastic concentrations showed distinct shifts in bacterial community composition. Populations of Actinobacteria, a group that specializes in breaking down complex carbon compounds, declined by an average of 19 percent. Meanwhile, populations of Proteobacteria, which tend to process simpler carbon sources and multiply quickly when nutrients are abundant, increased by 23 percent.
This shift matters because Actinobacteria produce enzymes that break down recalcitrant compounds like lignin and chitin, converting them into stable humus. Proteobacteria, while important for nutrient cycling, tend to produce carbon dioxide more quickly and contribute less to long-term carbon storage. The changing ratio suggests that soils contaminated with microplastics may release more carbon as greenhouse gases rather than storing it.
The Massachusetts team used isotope labeling to track the fate of carbon from decomposing corn stalks. They added stalks containing carbon-13, a stable isotope that acts as a tracer, to soil samples with varying microplastic levels. After 90 days, soils with high microplastic content had incorporated 16 percent less labeled carbon into stable organic matter fractions. More of the labeled carbon appeared as carbon dioxide in the headspace of the experimental containers, indicating increased respiration relative to storage.
Genetic sequencing revealed changes in microbial gene expression related to carbon metabolism. Genes encoding enzymes for breaking down complex polysaccharides were downregulated in high-microplastic soils, while genes for processing simple sugars were upregulated. The pattern suggested that microbial communities were shifting toward a fast-cycling metabolism that favors rapid growth over the production of stable soil carbon.
"We're seeing a fundamental change in how these communities process carbon," Dr. Gutknecht said. "The microbes aren't dying, but the community is reorganizing in ways that make the soil a less effective carbon sink."
Field Studies Link Microplastic Contamination to Reduced Soil Carbon Stocks
To determine whether laboratory findings translate to real-world impacts, researchers at Wageningen University in the Netherlands conducted a multi-year study of 60 agricultural fields with varying degrees of microplastic contamination. The fields had received different amounts of plastic mulch, compost containing plastic fragments, and sewage sludge, which often carries microplastics from synthetic textiles and personal care products.
The team measured soil organic carbon stocks at the start of the study and again after several years, controlling for factors like crop type, tillage practices, and fertilizer use. Fields in the highest contamination category, with more than 3 microplastic particles per gram of soil, showed an average decline in total soil organic carbon. Fields in the lowest category, with fewer than 0.5 particles per gram, showed an increase over the same period.
The difference was statistically significant and represented a substantial shift in carbon storage capacity. The researchers calculated that if microplastic contamination continues to increase at current rates, agricultural soils in Western Europe could face significant challenges in maintaining their role as carbon sinks, potentially releasing substantial amounts of carbon dioxide equivalent annually.
Soil respiration measurements taken quarterly throughout the study showed that high-contamination fields released 12 to 18 percent more carbon dioxide during spring and fall, when microbial activity peaks. The extra emissions came primarily from the rapid decomposition of fresh organic matter rather than from old, stable carbon, suggesting that microplastics were disrupting the initial stages of decomposition when plant material is first colonized by microbes.
The Dutch team also documented changes in soil structure. Microplastics interfered with the formation of aggregates, the clumps of soil particles bound together by microbial secretions and fungal hyphae. Aggregates protect organic matter from decomposition by physically isolating it from microbes and oxygen. Fields with high microplastic content had 24 percent fewer stable aggregates, leaving more organic matter exposed to decomposition.
"Soil carbon storage depends on a complex interplay between microbial activity and physical protection," said Dr. Franciska de Vries, who led the Wageningen study. "Microplastics disrupt both sides of that equation."
The researchers found that not all plastics had equal effects. Polyethylene, commonly used in plastic bags and mulch films, caused more disruption than polypropylene, used in packaging and textiles. Biodegradable plastics marketed as soil-friendly alternatives showed intermediate effects, still altering microbial communities but to a lesser degree than conventional plastics. However, even biodegradable plastics persisted long enough to cause measurable changes in carbon cycling.
Mounting Evidence of Global Contamination
Microplastic contamination of agricultural land is increasing across multiple pathways. Plastic mulch films, used on more than 20 million hectares worldwide to conserve moisture and control weeds, leave behind fragments when removed. Compost made from municipal organic waste often contains microplastics from food packaging and compostable serviceware. Sewage sludge applied as fertilizer carries plastic fibers from laundry and microbeads from cosmetics. Atmospheric deposition adds particles that have been transported by wind from roads, landfills, and oceans.
Research has documented microplastics in agricultural soils on every continent, with concentrations in intensively farmed regions of Europe and Asia sometimes exceeding those in ocean sediments. The particles accumulate because they degrade slowly, with residence times in soil estimated at decades to centuries depending on polymer type and environmental conditions.
According to a review published in Nature Geoscience, terrestrial environments now contain substantial microplastic pollution. The authors estimated that soils receive between 4 and 23 times more microplastic mass annually than oceans, primarily through agricultural inputs and atmospheric deposition. Urban and peri-urban agricultural areas showed the highest contamination levels, but even remote farmland showed detectable concentrations.
A comprehensive assessment by the Food and Agriculture Organization of the United Nations examined the scope of microplastic contamination in agricultural systems worldwide. The report documented the presence of microplastics in soils across diverse agricultural regions and identified multiple pathways through which plastic particles enter farming systems. The analysis highlighted the need for better understanding of how these contaminants affect soil health and agricultural productivity.
What This Means
The convergence of laboratory experiments, controlled field studies, and observational research presents a consistent picture: microplastics are altering fundamental soil processes in ways that could have significant consequences for climate and agriculture.
Global soils contain an estimated 2,500 gigatons of carbon, more than three times the amount in the atmosphere and four times the amount in all living plants and animals. Even small changes in the rate at which soils accumulate or release carbon can have outsized effects on atmospheric carbon dioxide concentrations. A 1 percent loss of carbon from global agricultural soils would release roughly 25 gigatons of carbon dioxide, equivalent to more than half of annual global emissions from fossil fuels.
The implications extend beyond carbon storage. Soil microbes also regulate nitrogen cycling, suppress plant diseases, and produce compounds that improve soil structure. Disruptions to these communities could reduce crop yields, increase dependence on synthetic fertilizers, and make agriculture more vulnerable to drought and erosion. Some researchers worry about cascading effects as changes in microbial communities alter the larger soil food web, affecting earthworms, insects, and other organisms that depend on microbial activity.
Policy responses have focused primarily on reducing plastic waste entering oceans, but terrestrial ecosystems may face equal or greater risks. The European Union has restricted certain single-use plastics and is developing standards for biodegradable mulch films. California requires labeling of compost products that contain detectable microplastics. However, no jurisdiction has established limits on microplastic concentrations in agricultural soils or systematic monitoring programs.
Some agricultural practices could reduce contamination. Switching from plastic mulch to organic alternatives like straw or cover crops eliminates a major source. Screening compost to remove visible plastic fragments and limiting sewage sludge application can reduce inputs. However, atmospheric deposition and legacy contamination from past practices will continue to add microplastics even if new inputs cease.
Researchers are exploring whether soil management can mitigate the effects of existing contamination. Adding biochar, a charcoal-like material made from plant waste, may provide surfaces for microbial colonization that compete with plastic particles. Inoculating soil with specific microbial strains that are less sensitive to plastic exposure could maintain decomposition rates. Some microbes can break down certain plastics, though the process is slow and produces breakdown products whose effects are poorly understood.
Climate Interactions and Future Trajectories
The interaction between microplastics and climate change adds urgency to the issue. As temperatures rise, microbial activity generally increases, accelerating decomposition and carbon release. If microplastics simultaneously reduce the efficiency of carbon storage, the two factors could combine to create a stronger feedback loop than either would produce alone. Soils in tropical and subtropical regions, which contain large carbon stocks and are warming rapidly, may be particularly vulnerable.
Scientists emphasize that much remains unknown. Most studies have focused on a handful of plastic types and microbial species under controlled conditions. Real soils contain thousands of microbial species and complex mixtures of plastic polymers, additives, and breakdown products. The long-term trajectory of contaminated soils is unclear. Microbial communities might adapt to plastic presence, restoring normal function, or disruptions might intensify as plastics break into smaller nanoplastic particles that can enter microbial cells.
Field studies tracking the same sites over decades will be essential for understanding whether current trends continue or whether ecosystems develop resilience. Researchers are establishing long-term monitoring plots in agricultural regions across North America, Europe, and Asia to track changes in microplastic concentrations, microbial community composition, and carbon storage over time.
The economic implications are substantial. Agriculture depends on soil fertility, which in turn depends on healthy microbial communities. If microplastic contamination reduces soil productivity, farmers may need to apply more fertilizer to maintain yields, increasing costs and environmental impacts. Reduced carbon storage could undermine efforts to use agricultural soils as carbon sinks in climate mitigation strategies, forcing greater emissions reductions in other sectors.
Some researchers argue for a precautionary approach, limiting new sources of soil microplastic contamination even before all mechanisms and consequences are fully understood. Others emphasize the need for better data to guide policy, noting that overly restrictive regulations could impose costs without clear benefits if impacts prove less severe than current evidence suggests.
International scientific bodies are beginning to address the knowledge gaps. Research consortia in Europe and North America are coordinating multi-site experiments to standardize methods and compare results across different soil types and climates. These collaborative efforts aim to provide the robust evidence base needed for informed policy decisions.
The challenge extends beyond agriculture. Microplastics have been found in forests, grasslands, and other terrestrial ecosystems that also play important roles in carbon storage. Understanding how plastic contamination affects these systems will require sustained research investment and coordination across disciplines including soil science, microbiology, ecology, and climate science.
"We're watching a global experiment unfold in real time," Dr. Weber said. "By the time we fully understand the consequences, they may be difficult to reverse."
The challenge facing scientists and policymakers is to act on incomplete information, balancing the risks of premature action against the potentially irreversible consequences of delay. As microplastic concentrations in agricultural soils continue to rise, the window for preventing widespread disruption of soil carbon storage may be narrowing. The emerging evidence suggests that addressing microplastic contamination should be considered an integral part of climate change mitigation and agricultural sustainability strategies, alongside efforts to reduce greenhouse gas emissions and improve soil management practices.