Researchers find that soil aging of polyethylene microplastics has only a limited effect on their interactions with organic contaminants. Scientists have long worried that aging microplastics in soil could become increasingly effective at interacting with organic contaminants.
A new study shows that this may not be the case for all plastic types. Researchers found that while polyethylene microplastics change as they age in soil, those changes have little effect on how they interact with various organic contaminants.
For years, scientists have wondered whether tiny plastic fragments (i.e., microplastics) in farmland might behave like miniature chemical sponges—absorbing pesticides, pharmaceuticals and other organic contaminants, potentially altering their environmental behavior and overall fate. But a new study suggests those fears may have been overstated for plastics as a whole.
Researchers found that even after spending nearly two years buried in agricultural soil, one of the world's most common microplastics (linear low-density polyethylene, widely used in agricultural films, including greenhouse covers and mulch films) did not become significantly more effective at interacting with organic contaminants. Instead, the study shows that the soil itself—not the plastic—remains the main factor influencing the environmental fate of these chemicals.
Published in Soil & Environmental Health, the study was led by Ph.D. student Yuval Shahar, Dr. Evyatar Ben Mordechay and professor Benny Chefetz of the Hebrew University. To test what really happens under field conditions, the researchers buried fragments of polyethylene previously used as mulch film in three different Israeli agricultural soils for 20 months.
Surface changes, limited chemical impact
When the team dug up the particles, they found exactly what scientists expected: The plastics had changed. Natural organic matter had coated their surfaces, altering their surface chemistry. Many researchers have assumed that this kind of aging would turn microplastics into increasingly effective "chemical sponges" capable of interacting more strongly with organic contaminants.
The researchers tested how the aged microplastics interacted with 48 organic contaminants commonly found in reclaimed wastewater used for agricultural irrigation worldwide, including pesticides, pharmaceuticals and other wastewater-derived compounds. For about 90% of the chemicals, aging made little or no meaningful difference. The contaminants sorbed only weakly to the plastics and were released just as easily, indicating that the interactions were largely weak and reversible rather than permanently trapping the chemicals.
"Our findings challenge a common assumption that aging dramatically increases the environmental risk posed by polyethylene microplastics," said Ben Mordechay.
"Although the particles clearly change after spending months in soil, these surface modifications translate into only minimal changes in their interactions with most contaminants. In agricultural soils, natural soil components remain far more important than the microplastics themselves in determining where these chemicals end up."
Soil differences changed little
The study also found that differences between soils, including their organic matter and clay content, had almost no effect on the microplastics' aging or their interactions with the tested contaminants. Most surface changes occurred within the first year and were mainly associated with the formation of an organic coating, after which the particles remained relatively stable.
The researchers emphasize that microplastics remain an important environmental concern because of the large amounts entering the environment, their high persistence and their continued accumulation in agricultural soils. However, the new findings suggest that the role of some microplastics in interactions with organic contaminants has likely been overestimated.
"Microplastics are still an environmental problem, but our results help clarify where the greatest risks actually lie," said Chefetz. "When it comes to the behavior of these contaminants in agricultural soils, the soil itself, not the plastic, is doing most of the work. Understanding that distinction allows us to make more accurate environmental risk assessments and better focus future research and mitigation efforts."
Evidence from field-aged particles
The findings provide one of the most comprehensive real-world examinations to date of how soil-aged agricultural microplastics interact with a broad range of contaminants.
Rather than playing a major role in the environmental behavior of organic contaminants, the researchers conclude that polyethylene microplastics play only a minor role compared with the soil itself, whose minerals and organic matter remain the dominant factors influencing the environmental fate of organic contaminants.
More information
Yuval Shahar et al, Aging of polyethylene microplastics in agricultural soils has minimal effect on sorption and desorption of wastewater-derived organic contaminants, Soil & Environmental Health (2026). DOI: 10.1016/j.seh.2026.100207
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Citation: Do aging microplastics increase environmental risks from organic contaminants? Study suggests less than expected (2026, August 4) retrieved 4 August 2026 from https://phys.org/news/2026-08-aging-microplastics-environmental-contaminants.html
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