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Earthworms’ Degradable Bioplastic Diet of Polylactic Acid: Easy to Break Down and Slow to Excrete
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Researchers found that earthworms preferred ingesting both PET and PLA microplastics over clean soil, but bio-based PLA was more easily broken down in their guts while being excreted more slowly than fossil-based PET, raising concerns about bioplastic accumulation in soil organisms.
Microplastics (MPs) in soils may be ingested by terrestrial animals. While the application of bioplastics is increasing, the ingestion and excretion characteristics of bio-MPs by terrestrial animals are poorly understood as compared to fossil-MPs. Here, the approach-avoidance behavior of adult earthworms Eisenia fetida to MP-contaminated soil was assessed. Fossil-based poly(ethylene terephthalate) (PET) and bio-based poly(lactic acid) (PLA) MPs were found to be preferred by the earthworms, which might be due to the odor of polymer monomers. MPs in earthworm casts were analyzed by microscopy counting and liquid chromatography-tandem mass spectrometry. The amount of microscopically recognizable excreted PET and PLA was 553 and 261 items/g, respectively, while a higher proportion of smaller PLA particles also presented. Bio-based PLA is much easy to break down by earthworms than fossil-based PET. Submicron and nanocron PLA accounted for 57 and 13% of the excreted PLA on the 10th day of excretion. MP excretion was well described with the first-order kinetic model, and the elimination half-life was 9.3 (for PET) and 45 h (for PLA). A longer excretion period of PLA may be related to its potential to break down in the earthworms' digestive tract. This not only promotes the environmental degradation of PLA but also suggests the ecological risk caused by nanoparticles.
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Polylactic acid degradation is enhanced by microbial processes in earthworm guts
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Polylactic acid (PLA), a compostable bioplastic, was found to degrade more rapidly when it passes through earthworm guts due to microbial activity in the earthworm digestive system. This suggests that earthworms may play a role in accelerating the breakdown of biodegradable plastics in soil. However, if PLA degrades incompletely it could still generate microplastic fragments, so biodegradability claims need to be evaluated under realistic soil conditions.
Short-Term Effect of Poly Lactic Acid Microplastics Uptake by Earthworms, Eudrilus eugeniae.
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Researchers tested whether earthworms (Eudrilus eugeniae) would ingest polylactic acid (PLA) biodegradable microplastics when mixed with organic matter, finding they did but with reduced weight gain and reproductive output at higher concentrations. This suggests even biodegradable microplastics can harm soil organisms, which are essential for nutrient cycling and soil health.
Comparison of the potential toxicity induced by microplastics made of polyethylene terephthalate (PET) and polylactic acid (PLA) on the earthworm Eisenia foetida
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Researchers compared the toxicity of microplastics made from conventional PET plastic and biodegradable PLA plastic on earthworms. Surprisingly, the supposedly eco-friendly PLA particles caused more harm than PET, triggering oxidative stress, tissue damage, and behavioral changes in the worms. This challenges the assumption that bioplastics are always safer for soil organisms than traditional plastics.
Short-term effect of poly lactic acid microplastics uptake by Eudrilus eugenia
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This study investigated whether the earthworm Eudrilus eugeniae could degrade polylactic acid (PLA) microplastics by feeding them mixtures of PLA and cow dung for 16 days. Earthworms did not degrade the PLA, and high concentrations (80% PLA) reduced weight gain, but the PLA-rich vermicast may support further microbial degradation due to its rich microbial environment.
Earthworms Exposed to Polyethylene and Biodegradable Microplastics in Soil: Microplastic Characterization and Microbial Community Analysis
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Researchers exposed earthworms to biodegradable and conventional polyethylene microplastics in natural soil and found that worms ingested both types. The biodegradable plastic showed signs of partial breakdown in the earthworm gut, while conventional polyethylene remained unchanged. Although microplastics did not significantly alter the soil or gut microbiome in this study, the results confirm that earthworms transport microplastics through soil ecosystems.
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