Biodegradable Microplastics Alter Soil Properties While Composting Weakens Several Observable Effects

Biodegradable microplastics alter fundamental soil chemical and structural properties, whereas conventional polyethylene fragments show no measurable effects over a two-month period under controlled conditions, according to new research published in Frontiers in Soil Science. The laboratory study demonstrates that the magnitude and direction of changes in soil properties depend heavily on the specific polymer composition and whether the plastic enters the soil in a pristine condition or following an organic composting process.

Agricultural soils face increasing exposure to microplastics through direct plastic use, such as agricultural mulching films, as well as via organic amendments and fertilizers containing residues of materials degraded during composting. Researchers sought to resolve how the degradation state of these particles interacts with environmental physical stress cycles, such as alternating freeze-thaw and drying-rewetting episodes, to alter the physicochemical characteristics of soil over time.

To evaluate these dynamics, an investigation led by Melissa Bakhos, Cornelia Rumpel, Marie-France Dignac, and their colleagues tested a Cambisol under controlled laboratory conditions. The team exposed four soil incubation replicates to three distinct plastic types at a concentration of 1% weight-by-weight: a standard conventional polyethylene film alongside two biodegradable alternatives, consisting of an ethylcellulose-based film and a blend of poly(butylene adipate terephthalate) and starch.

The experimental protocol incorporated plastic materials introduced either in their pristine state or after undergoing prior composting. The researchers conducted the soil incubations over a 59-day period under both constant climatic conditions and regimes featuring alternating physical stress cycles. At the conclusion of the 59 days, all visible plastic fragments were systematically removed from the soil samples before conducting physical measurements.

This deliberate removal allowed the team to evaluate the lasting legacy effects of the incubation process itself on soil physical properties rather than the immediate physical presence of macro-fragments, though researchers noted that chemical leachates or microscopic plastic fragments could still remain within the substrate. Following fragment extraction, the authors evaluated soil physicochemical parameters, soil aggregation characteristics, and soil organic carbon composition using Rock-Eval pyrolysis.

The resulting measurements showed that soil responses were governed primarily by plastic type and degradation history. Conventional polyethylene microplastics produced no statistically significant changes in any of the measured soil parameters over the 59-day incubation, irrespective of whether the polyethylene was applied in a pristine or composted form. In contrast, biodegradable polymers induced noticeable, state-dependent modifications to the soil matrix.

Pristine particles of both the PBAT/starch blend and the ethylcellulose-based material significantly altered soil pH and electrical conductivity while increasing the mean weight diameter of soil aggregates. Composting notably attenuated several of these shifts, especially for the PBAT/starch material. For the ethylcellulose-based microplastics, prior composting diminished impacts on mean weight diameter and soil organic carbon content, but caused opposite directional shifts in soil pH and electrical conductivity compared to its pristine counterpart.

Physical environmental stress further modulated these interactions. Alternating cycles of drying-rewetting and freeze-thaw selectively adjusted specific properties in a manner dependent on both polymer type and treatment history, with observable impacts predominantly centered on mean weight diameter, soil pH, and electrical conductivity. The authors emphasize that biodegradable plastics do not interact uniformly with soil systems, highlighting the complex influence of prior weathering and physical stress cycles on agricultural soil environments.

The research collaboration brought together investigators from several French scientific institutions, including the Institut d’écologie et des sciences de l’environnement de Paris at Sorbonne Université, CNRS, INRAE, IRD, UPEC, and Université Paris Cité, alongside the Agence de l’Environnement et de la Maitrise de l’Energie in Angers, the Laboratoire de Biotechnologie de l’Environnement at INRAE and Université de Montpellier in Narbonne, and IFP Energies nouvelles in Rueil-Malmaison. In addition to lead author Melissa Bakhos, the study was conducted by Dominique Patureau, Isabelle Kowalewski, Philippe Biron, and Axel Felbacq, with Marie-France Dignac serving as the corresponding author for the project.

Although visible plastic pieces were meticulously taken out at the end of the 59-day incubation period, the researchers noted that chemical leachates or microscopic plastic fragments could remain within the soil matrix, meaning the observed outcomes reflect incubation consequences following visible fragment removal rather than an entirely plastic-free medium. Furthermore, the findings are derived specifically from laboratory exposures of a single Cambisol soil type tested under controlled environmental conditions, underscoring that broader generalizations across differing soil textures or field environments require caution.

The published findings contribute directly to discussions surrounding soil organic matter dynamics and carbon sequestration, representing an original research investigation received in August 2026 and accepted for publication in October 2026.

Subject of Research: Influence of biodegradable microplastic degradation and environmental stress on soil properties

Article Title: Influence of biodegradable microplastic alteration during composting and drying/rewetting cycles on soil physicochemical properties

Article References: Bakhos, M., Rumpel, C., Patureau, D., Kowalewski, I., Biron, P., Felbacq, A., & Dignac, M.-F. (2026). Influence of biodegradable microplastic alteration during composting and drying/rewetting cycles on soil physicochemical properties. Frontiers in Soil Science, 6, 1958556. https://doi.org/10.3389/fsoil.2026.1958556

Image Credits: AI Generated

DOI: 10.3389/fsoil.2026.1958556

Keywords: microplastics, biodegradable plastics, soil science, composting, polyethylene, PBAT, starch blend, ethylcellulose, soil properties, Cambisol, soil pH, electrical conductivity, mean weight diameter, soil aggregation, drying-rewetting cycles, freeze-thaw cycles, soil organic carbon, Rock-Eval pyrolysis