A new greenhouse investigation has demonstrated that earthworms may serve as an effective biological countermeasure against microplastic pollution in agricultural soils. The study shows that the presence of earthworms significantly improves plant performance in soil contaminated with polypropylene microplastics, highlighting the potential of nature-based strategies to mitigate an emerging environmental challenge.

The research examined the response of Chinese milk vetch, a widely used green manure crop that supports soil fertility through nitrogen fixation. Plants were grown in controlled conditions using soils artificially amended with varying concentrations of microplastic particles smaller than 5 millimeters—fragments that have become pervasive in farmland due to global increases in plastic production and inadequate waste management. These particles can alter soil structure, disrupt nutrient exchange, and interfere with root function, making them a subtle but growing stressor for food production systems.

In soils containing one percent polypropylene microplastics, plant height decreased by approximately 28 percent, while shoot dry weight declined by about 20 percent. When earthworms were introduced into these same soils, plant growth rebounded markedly. Heights increased by roughly 50 percent, and shoot dry weight rose by more than 30 percent relative to microplastic-only conditions. These results indicate that earthworms can partially offset the adverse effects of microplastic contamination on plant development.

Beyond visible growth improvements, earthworms enhanced multiple aspects of soil quality. Their activity increased levels of organic carbon, total nitrogen, ammonium nitrogen, and available phosphorus—nutrients that underpin crop performance. These improvements were most pronounced in the rhizosphere, the narrow soil zone surrounding roots, where nutrient turnover accelerated. Enzymatic activity also rose significantly, with marked increases in acid phosphatase, urease, and sucrase—key indicators of nutrient release and microbial metabolism. Such changes point to more dynamic nutrient cycling and improved biochemical functioning under earthworm influence.

Soil microbial communities likewise shifted in composition and structure. Bacterial groups associated with carbon utilization and phosphorus mobilization became more prevalent, whereas taxa linked to stress responses decreased. The microbial network exhibited greater connectivity and stability, suggesting enhanced resilience against ongoing pollution pressure. A modest decline in soil pH was also observed in the presence of earthworms, reinforcing conditions that can facilitate nutrient availability and uptake.

The study further identified changes occurring within plant roots. Activity in the ribosome—the cellular machinery responsible for protein synthesis—was elevated, indicating stronger capacity for cellular repair and growth under stress. Gene expression patterns in the root transcriptome also shifted, with upregulation observed in pathways supporting sugar metabolism, energy production, and pigment formation. These physiological responses suggest that earthworms assist plants not only by improving the soil environment but also by supporting internal mechanisms that enable tolerance to microplastic stress.

Earthworms, often referred to as ecosystem engineers, are known for their ability to restructure soil through burrowing, enhance aeration and water infiltration, and enrich soil organic matter. These inherent traits appear to counteract several of the disruptions caused by microplastics, which can impede root–soil interactions and restrict nutrient flow. As a result, earthworms may offer a low-cost, scalable tool for maintaining soil health in contaminated areas.

The findings arrive at a time when microplastic accumulation in terrestrial environments is increasingly recognized as a global issue. Estimates suggest that more than 80 percent of microplastics released to land ultimately reach agricultural soils, raising concerns about long-term impacts on soil fertility and crop productivity. While the study’s results are promising, the researchers noted that the microplastic concentrations used in the experiments exceed typical field levels and that earthworms themselves may be susceptible to certain forms of plastic pollution. This underscores the need for field trials across diverse crop systems, soil types, and climate conditions.

Although nature-based interventions alone cannot resolve the broader plastic pollution crisis, they may offer practical benefits for farmers seeking to maintain yields and reduce reliance on synthetic fertilizers. Enhancing the performance of green manure crops such as Chinese milk vetch through earthworm activity could become one component of integrated soil management strategies.

The findings are published in Environmental Chemistry and Ecotoxicology.