Soils store more carbon than the atmosphere and all vegetation combined, and saline-alkali soils—degraded lands where salt accumulation suppresses plant growth and microbial activity—represent a vast and expanding category under pressure from irrigation practices, climate change, and intensifying agriculture. At the same time, plastic fragments have infiltrated agricultural soils worldwide through mulching films, irrigation with contaminated water, sewage sludge application, and the slow breakdown of larger plastic debris. Because microorganisms carry out nearly all of the chemical transformations that determine whether soil carbon remains locked away or escapes into the atmosphere as carbon dioxide, any pollutant that reshapes microbial communities has the potential to alter the global carbon balance. What has remained murky is how different types of microplastics interact with salinity—a stress factor that itself profoundly constrains microbial metabolism.

To disentangle these effects, the team combined carefully controlled laboratory incubation experiments with metagenomic sequencing, a technique that reads the collective genetic blueprint of entire soil microbial communities without the need to culture individual species in the laboratory. Soils were exposed to two microplastic types: polyethylene, the durable conventional plastic that fragments into particles persisting for decades or centuries, and polylactic acid, a biodegradable polymer derived from plant starch that microorganisms can enzymatically hydrolyze and ultimately metabolize. Each plastic was added at four concentrations—0, 0.5, 1, and 14 percent by weight—spanning the range from environmentally realistic contamination levels to high-dose experimental conditions. Critically, the researchers crossed these treatments with three salinity levels, expressed as electrical conductivity values of 4.75, 20, and 40 mS/cm, creating a matrix of conditions that allowed them to separate the influence of plastic type, dose, and salt stress.

The first major finding concerned microbial diversity. Across the board, the addition of microplastics increased microbial richness in the soils, indicating that plastic particles—even inert polyethylene—provide new niches or substrates that allow more microbial species to coexist. But the deeper story emerged when the researchers measured carbon pools directly. Polylactic acid significantly increased soil organic carbon by between 0.96 and 118.71 percent compared with polyethylene, and boosted soil microbial biomass carbon—an indicator of living microbial mass—by 9.18 to 362.46 percent. These are enormous effects by soil science standards, and they point to a fundamental asymmetry: not all microplastics disturb soil carbon cycling in the same way, and biodegradable plastics may actively stimulate the biological processes that build carbon stocks rather than degrade them.

The metagenomic data revealed exactly how this stimulation occurs. Genes associated with carbon fixation—the processes by which microorganisms convert inorganic carbon dioxide into organic biomass—responded differently to the two plastics. Polylactic acid enhanced carbon fixation primarily through two of the most celebrated biochemical pathways in biology: the Calvin–Benson–Bassham cycle, the same route that plants use in photosynthesis, whose key gene Prk increased in relative abundance by 3.31 to 98.43 percent, and the Wood–Ljungdahl pathway, an ancient carbon-fixation route used by anaerobic bacteria and archaea, whose acsABCDE genes rose by 0.035 to 0.44 percent. Polyethylene, by contrast, stimulated the 3-Hydroxypropionate cycle, with the mcr gene increasing by 17.3 to 163.06 percent—a pathway typically associated with certain autotrophic microbes that thrive in specialized environments.

Energy metabolism shifted as well. Polyethylene addition increased the metabolic activity of the tricarboxylic acid cycle, the central energy-generating hub of cellular respiration, by 0.8 to 26.67 percent, suggesting that the conventional plastic pushes microbial communities toward greater oxidative breakdown of organic matter—processes that can ultimately release carbon dioxide. Meanwhile, both plastic types promoted the relative abundance of genes involved in ethanol fermentation, including adh, mdh, and ald, hinting that microplastic exposure drives microbes toward fermentative metabolism, a less efficient mode of energy production that flourishes when environments become chemically stressful or oxygen-limited.

Salinity proved to be a decisive modifier of all these effects. The relative abundance of several carbon fixation genes was higher under low-to-medium electrical conductivity conditions than at the highest salinity level, where the enhanced fermentation pathways suggested a more complex and potentially less efficient carbon cycle. In other words, salt stress appears to push microbial communities away from carbon sequestration and toward metabolic coping strategies. This interaction matters because saline-alkali soils are already metabolically constrained environments; the study suggests that microplastic contamination in these lands cannot be evaluated in isolation from the salt regime.

Broader functional predictions based on the Kyoto Encyclopedia of Genes and Genomes pathway database added a further layer of nuance. Polylactic acid treatments exhibited greater changes in functional pathway abundance in response to varying salinity than polyethylene treatments, indicating that the biodegradable plastic’s effects are more sensitive to—and potentially more responsive to—environmental context. Polyethylene addition increased the abundance of general metabolic pathways but decreased the abundance of pathways devoted to translation, replication, and DNA repair, the fundamental maintenance operations of cells. That suppression is a biochemical red flag: it suggests that polyethylene exposure may impair microbial growth and genomic integrity even as it superficially stimulates metabolism. Polylactic acid, in contrast, showed a stronger capacity to promote cellular processes, consistent with a polymer that microbes can actively consume as a carbon source rather than merely endure.

The implications ripple outward in several directions. First, the work complicates the popular assumption that biodegradable plastics are automatically benign—or automatically harmful—in soil environments. Here, polylactic acid fragments appear to feed microbial communities, enrich carbon-fixing pathways, and build microbial biomass, potentially supporting carbon storage in soils that are otherwise carbon-poor. But the study also raises questions: if biodegradable plastics accelerate microbial activity, they may equally accelerate the decomposition of existing organic matter under some conditions, and long-term field studies will be needed to confirm whether the laboratory carbon gains persist. Second, the findings underscore that polyethylene, even when it does not serve as food for microbes, exerts selective pressure that can suppress genetic maintenance functions across communities—a subtle form of physiological stress that could erode the resilience of soil ecosystems over time.

There is also a geographic urgency to the work. Inner Mongolia, where the research team is based, sits at the heart of China’s vast saline-alkali belt, where decades of irrigation, land conversion, and climate pressure have degraded millions of hectares. These same regions rely heavily on plastic mulch films to conserve soil moisture and boost crop yields, creating an intimate overlap between plastic contamination and soil salinization. Understanding how these two stressors interact is therefore not an academic curiosity but a practical necessity for land managers weighing the trade-offs of agricultural plastic use on marginal lands.

The methodological approach itself represents a growing trend in environmental microbiology. Rather than measuring bulk carbon changes alone, the team interrogated the functional genes of entire communities, allowing them to pinpoint which biochemical pathways—Calvin cycle, Wood–Ljungdahl, 3-hydroxypropionate, TCA cycle, fermentation—shifted under each treatment. This gene-level resolution transforms what could have been a simple pollution study into a mechanistic account of how polymer chemistry propagates through microbial metabolisms to alter ecosystem-scale carbon fluxes.

As microplastic production continues its relentless rise and soil salinization expands across arid and semi-arid regions worldwide, the intersection of these two global challenges will only grow more consequential. This study provides a template—and a warning: the carbon future of degraded soils may depend not just on how much plastic enters the ground, but on what kind, and how salty the ground beneath it has become.

Microplastics are increasingly common in agricultural landscapes, where they can enter soil through degraded greenhouse coverings, mulch films, irrigation water, sewage sludge and atmospheric deposition. Because these particles can remain in the environment for decades, researchers have questioned whether they might accumulate contaminants and transport them through soil, groundwater or food-production systems. The concern is particularly significant in regions where reclaimed wastewater is used to irrigate crops.

The study focused on linear low-density polyethylene, a flexible plastic widely used in agricultural films. Researchers buried fragments of previously used polyethylene mulch film in three different Israeli agricultural soils and allowed them to remain underground for 20 months. This approach was designed to reproduce environmental aging under realistic conditions rather than relying solely on accelerated laboratory treatments, which can produce surface changes that do not fully reflect what occurs in the field.

When the scientists recovered the plastic fragments, the particles had clearly changed. Natural organic matter from the soil had accumulated on their surfaces, forming a coating known as an environmental or soil-derived corona. Such coatings can alter surface chemistry, wettability and the availability of binding sites. In theory, these changes could increase the particles’ capacity to attract hydrophobic organic molecules, leading to stronger sorption and potentially allowing microplastics to act as mobile carriers of pollution.

To test that possibility, the researchers examined the interaction between the aged polyethylene and 48 organic contaminants commonly detected in reclaimed wastewater used for agricultural irrigation. The chemical set included pesticides, pharmaceuticals and other wastewater-associated compounds with different molecular properties. The team measured both sorption, the process by which contaminants attach to a surface, and desorption, the process by which they are released back into the surrounding environment.

The results challenged the assumption that aging automatically makes polyethylene microplastics more chemically active. For approximately 90 percent of the tested compounds, soil aging caused little or no meaningful change in the amount of contaminant associated with the plastic. Overall, the compounds interacted only weakly with the polyethylene and could be released relatively easily. That pattern indicates that the plastic did not permanently trap most of the chemicals or become a substantially more powerful contaminant carrier over time.

The researchers also found that the largest changes to the plastic surfaces occurred during the first year of burial. After that initial period, the particles became comparatively stable, suggesting that the formation of the organic coating reached a plateau. Surprisingly, differences among the three soils—including their organic matter and clay content—had little influence on how the polyethylene aged or how it interacted with the contaminants. This does not mean soil properties are unimportant; rather, it suggests that the soil matrix itself may dominate contaminant behavior more strongly than the aged plastic particles.

“Soil, not the plastic, remains the main factor influencing the environmental fate of these chemicals,” said Dr. Evyatar Ben Mordechay, one of the study’s researchers. Soil minerals, clay surfaces and native organic matter provide an enormous and chemically diverse network of binding sites. Compared with that complex matrix, the surface area and sorption capacity of polyethylene microplastics may be relatively minor, particularly when the particles are present at environmentally realistic concentrations.

The findings do not make microplastics harmless. Polyethylene fragments remain persistent pollutants, can accumulate in agricultural soils and may affect soil structure, organisms and ecosystem processes through other mechanisms. The study examined one plastic type, and different polymers, additives, particle sizes, shapes and weathering histories could behave differently. Even so, the research offers a more precise picture of their role in contaminant transport: for aged polyethylene in agricultural soils, the plastic appears to play a secondary part, while the soil itself continues to control the movement, retention and release of most organic pollutants.

Subject of Research: Cells
Article Title: Aging of polyethylene microplastics in agricultural soils has minimal effect on sorption and desorption of wastewater-derived organic contaminants
Web References: https://doi.org/10.1016/j.seh.2026.100207
References: Soil & Environmental Health, DOI: 10.1016/j.seh.2026.100207
Image Credits: Raz Lev

Keywords: Soil science, surface chemistry, environmental sciences, pollution, environmental chemistry, plastics, wastewater, microplastics, agricultural soils, organic contaminants

Microplastics, defined as plastic particles smaller than 5 mm, have penetrated various ecosystems and are now a prevalent concern for environmental scientists across the globe. The study bridges a significant gap in our understanding by providing a comprehensive assessment of microplastic levels specifically in agricultural soils in India, an area that has remained largely underexplored. This research marks a pivotal moment, drawing attention to the intersection of agricultural health and environmental contamination while simultaneously urging further exploration into this growing crisis.

The researchers employed rigorous methodologies to assess microplastic contamination in these regions, including systematic sampling across diverse agricultural locations. Utilizing advanced analytical techniques allowed them to identify and quantify microplastic pollutants effectively. Their meticulous approach not only underscores the importance of scientific rigor in environmental assessments but also sets a precedent for future studies aiming to address similar global issues.

Within the findings, the researchers disclosed various types of microplastics detected, ranging from fibers and fragments to microbeads. The diversity in microplastic types signifies the complex origins of these pollutants in the agricultural landscape. Furthermore, their study suggests that agricultural practices could further exacerbate the presence of microplastics in soils, highlighting a critical link between human actions and environmental degradation.

As the research unfolded, it became evident that the sources of microplastics in these agricultural lands were multifaceted. Possible contributors include urban runoff, agricultural inputs such as fertilizers and pesticides, and even atmospheric deposition. With these insights, the authors implore policymakers to take immediate action, as the implications of such pervasive contamination can lead to plant uptake of microplastics, potentially entering the human food chain.

The health ramifications associated with microplastics have generated much debate in scientific communities. The potential impacts on human health through the consumption of crops grown in contaminated soils cannot be overstated. It raises fundamental questions about food safety and public health, igniting a passionate discourse on the responsibilities of agricultural sectors, consumers, and regulatory bodies alike. The authors emphasize the need for increased awareness and education regarding microplastics, not just among farmers but across all sectors of society.

Moreover, the findings of this investigation play a pivotal role in educating the public about the importance of sustainable agricultural practices and the necessity of reducing plastic usage in daily life. The farmers, often seen as the custodians of the land, need to be integral players in combating this contamination issue through eco-friendly agricultural practices. The research calls for a collaborative approach involving farmers, scientists, and policymakers to develop efficient strategies to mitigate microplastic runoff into agricultural lands.

The environmental implications of microplastic contamination extend beyond agricultural soils. These pollutants can adversely affect the broader ecosystem, impacting soil health, plant growth, and ultimately the entire food web. The intricate relationships between soil microbes, plants, and surrounding wildlife could face severe disruption due to the pervasive presence of microplastics. As this ongoing research underscores the need for further ecological assessments, it becomes increasingly clear that microplastics are an urgent environmental issue that demands immediate and sustained attention.

What is particularly alarming is the continuous increase in microplastic generation and their longevity in the environment. Unlike organic pollutants that tend to degrade over time, plastics enter a cycle of persistent pollution, posing long-lasting threats to ecological systems. The researchers advocate for stringent regulations on plastic production and waste management to curb this insidious pollution, urging governments to take a stand in the fight against plastic waste.

This groundbreaking study, published in the journal Environmental Monitoring and Assessment, not only contributes to the scientific understanding of microplastics in agricultural settings but also holds the promise of galvanizing efforts towards a cleaner and healthier environment. By positioning itself at the forefront of environmental research, this paper serves as a crucial call-to-arms, prompting an urgent discussion about the prevention of microplastic pollution before it amplifies into a crisis beyond recovery.

In conclusion, the baseline assessment of microplastic contamination in agricultural soils in Karnataka and Goa serves as a wake-up call. It emphasizes a pivotal moment for the agricultural and environmental communities to collaborate in researching, managing, and solving pollution issues stemming from microplastics. The path forward requires not only scientific inquiry but also societal change, public awareness, and robust government policies. The health of our soils—and in extension, our health—is a delicate balance that requires immediate action to ensure a sustainable future for generations to come.

As more studies unfold in this area, and as the findings become widely known, awareness will continue to grow, shaping the narrative around our interaction with plastics and their impact on agriculture and the environment. Ultimately, the story of microplastics in agricultural soils is one of interconnectedness—a reminder of how human actions ripple through nature, affecting everything from soil health to food safety and environmental integrity.

Subject of Research: Microplastic contamination in agricultural soils from coastal Karnataka and Goa

Article Title: Baseline assessment of microplastic contamination in agricultural soils from the coastal stretches of Karnataka and Goa, Southwestern India

Article References:

Mahreen, L., C, A. & Warrier, A.K. Baseline assessment of microplastic contamination in agricultural soils from the coastal stretches of Karnataka and Goa, Southwestern India.
Environ Monit Assess 197, 1053 (2025). https://doi.org/10.1007/s10661-025-14513-5

Image Credits: AI Generated

DOI: 10.1007/s10661-025-14513-5

Keywords: Microplastics, agriculture, soil contamination, Karnataka, Goa, environmental assessment, food safety.