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Earthworm Casting Drives Soil Microplastic Upward Transport and the Formation of Biogenic Polymer Aggregates
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Scientists found that earthworms are moving tiny plastic particles (microplastics) from deeper soil up to the surface, where crops grow, and breaking them into even smaller pieces in the process. The earthworms also create conditions that help beneficial bacteria break down these plastics over time. This matters because it could affect how much plastic contamination gets into our food supply, though more research is needed to understand the full health implications.
Earthworms act as key ecosystem engineers influencing the distribution of soil microplastics (MPs), however, the residence, transport, and fate of these particles within the drilosphere, particularly within biogenic cast aggregates, remain poorly understood. Here, we combined a field survey of 43 paired soil-cast samples across three agricultural land-use scenarios with complementary laboratory soil column experiments to elucidate earthworm-driven MP dynamics. The field survey revealed ubiquitous in situ MP occurrence and upward fluxes from bulk soils to casts, with transport efficiency modulated by soil clay and organic carbon contents. Laboratory simulations using epigeic and anecic species validated that different ecotypes actively ingest MPs from source soils and deposit them in surface casts. Crucially, both field and laboratory data demonstrated a significant reduction in particle size in casts compared to soil (6.48% and 19.8%, respectively), supporting the potential earthworm effects on MP mechanical attrition. Polymer compositions in casts mirrored those in soils, exhibiting a nonselective and passive ingestion pathway. Beyond physical transport, the formation of field biogenic polymer aggregates facilitated chemical aging of MPs, as evidenced by elevated oxidation indices. This process was likely accelerated by the enrichment of plastic-degrading microbial taxa (e.g., Flavobacterium) within casts, which exhibited up to a 35.6-fold increase in relative abundance. Collectively, these findings highlight the dual role of soil-engineering invertebrates in driving the vertical redistribution and physicochemical degradation of MPs in agricultural systems.
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Microplastic transport in soil by earthworms
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Researchers demonstrated that earthworms can transport microplastic particles from the soil surface deeper into the ground, with smaller particles being moved to greater depths. Using the common earthworm Lumbricus terrestris in greenhouse experiments, they showed that worm activity significantly increased the presence of microplastics in lower soil layers. The findings suggest that earthworms play an important role in burying microplastics in soil, potentially affecting other soil organisms and groundwater.
Microplastics in Agricultural Soil: Fate, Impacts, and Bioremediation by Earthworms
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This review examines how microplastics accumulate in agricultural soils and the role earthworms may play in breaking them down. Researchers found that microplastics can harm soil health by disrupting microbial communities, enzyme activity, and nutrient availability, but that earthworms can enhance microplastic degradation through their digestive processes and the microorganisms in their gut. The study suggests that earthworm-based bioremediation could be a practical strategy for reducing microplastic contamination in farmland.
The deep-burrowing earthworm Lumbricus terrestris ingests and transports microplastic fibres of a wide length range in soils
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Scientists found that earthworms can eat and move tiny plastic fibers through soil, carrying pieces as long as 4.8 mm from the surface down to deeper layers. This matters because it shows how microplastics that contaminate soil from sources like synthetic clothing and plastic waste can spread underground through natural processes. Understanding how these plastic particles move through soil helps us better predict where they might end up in our food chain and environment.
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Researchers explored whether earthworms can break down microplastics in soil by passing them through their digestive systems. They found that earthworms fragmented and partially broke down polyethylene and biodegradable plastic particles, reducing their size and altering their chemical structure. This suggests earthworms could play a role in naturally reducing microplastic contamination in soil, though more research is needed to understand whether the smaller fragments pose their own risks.
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