Plastic pollution of the planet is one of the most serious environmental problems of our time. Plastic causes diverse and well-documented harm to aquatic ecosystems, from small invertebrates to fish, seals, and seabirds. Soils are also subject to large-scale plastic pollution, but its impact on soil inhabitants remains a subject of debate.
A team of scientists from the A.N. Severtsov Institute of Ecology and Evolution of the Russian Academy of Sciences (IEE RAS) and the Senckenberg Museum of Natural History (Germany) found that exposure to relatively large fragments (1–5 mm) of high-density polyethylene does not lead to weight loss in two common species of earthworms.
The study used the soil-dwelling, endogeozoic species Aporrectodea caliginosa and the leaf litter-feeding, epigeozoic species Lumbricus rubellus. It was assumed that ingesting plastic particles, which have no nutritional value, would cause weight loss in earthworms by diluting the food substrate (the so-called food dilution hypothesis). Despite initial expectations, in an 8-week experiment, the presence of plastic in the soil did not affect the body weight of earthworms, even at high concentrations (up to 2.3 weight percent in soil for A. caliginosa and up to 48 weight percent in leaf litter for L. rubellus). Both earthworm species actively ingested plastic particles, but no negative effects were observed.
It is likely that since plastic entering the soil has physical properties similar to various natural components of organic and mineral origin, it acts similarly and does not cause significant harm to soil inhabitants. This is a sharp contrast to the aquatic environment, where microplastics act as a “physical xenobiotic” that has no direct analogues, and explains why many studies of the effects of plastic on soil animals do not reveal any significant negative effects. However, long-term negative consequences cannot be ruled out, especially if plastic breaks down into smaller and potentially more dangerous nanoparticles.
The study was published in the journal Environmental Science and Pollution Research (Leonov, V.D., Zuev, A.G., Zueva, A.I., Sotnikov, I.V., Tiunov, A.V. (2025). Exposure to mm-scale microplastic particles does not cause weight loss in two earthworm species belonging to different ecological groups. Environ Sci Pollut Res.
