Potential use of earthworms to enhance decaying of biodegradable plastics

Authors: SANCHEZ-HERNANDEZ, JUAN - University Of Castilla-La Mancha(UCLM); CAPOWIEZ, YVAN - French National Institute For Agricultural Research; Ro, Kyoung

Submitted to: ACS Sustainable Chemistry & Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/11/2020
Publication Date: 2/11/2020
Publication URL: https://handle.nal.usda.gov/10113/6870052
Citation: Sanchez-Hernandez, J.C., Capowiez, Y., Ro, K.S. 2020. Potential use of earthworms to enhance decaying of biodegradable plastics. ACS Sustainable Chemistry & Engineering. 8(11):4292-4316. https://doi.org/10.1021/acssuschemeng.9b05450. Available: https://pubs.acs.org/doi/pdf/10.1021/acssuschemeng.9b05450.
DOI: https://doi.org/10.1021/acssuschemeng.9b05450

Interpretive Summary: Microplastics are defined as small plastic derived fragments less than 5 millimeter in size. Microplastic pollution in agricultural soils is an emerging environmental and health issue. Application of biosolids from sewage treatment plants, irrigation with reclaimed wastewater, and plastic mulching technology are the major sources of microplastic pollution in agroecosystems. Microplastics interact with soil physicochemical properties and biological processes, thus negatively affecting plant growth. Moreover, microplastics may be the carriers of environmental contaminants. Recent studies suggest that earthworms may facilitate plastic biodegradation directly and indirectly via their strong impact on soil microbial properties and the resulting intense soil bioturbation. The scope of this perspective paper is to stimulate the development of earthworm-based strategies for reducing microplastic pollution in agricultural soils. We introduce the current state of knowledge on microplastic-earthworm interaction and describe how earthworms may contribute to polymer biodegradation. We also propose a conceptual model using earthworms to reduce microplastic accumulation in soils when using plastic mulch films.

Technical Abstract: Microplastic pollution in agricultural soils is an emerging environmental and health issue. Application of biosolids, irrigation with reclaimed wastewater, and plastic mulching technology are the major sources of microplastic pollution in agroecosystems. Accumulating evidence suggests that microplastics interact with soil physicochemical properties and biological processes, thus negatively affecting plant growth. Moreover, microplastics may be the carriers of environmental contaminants (e.g., pesticides), acting as secondary sources of soil pollution. In an attempt to alleviate plastic pollution in soil, synthetic- and natural-based biodegradable mulch films are replacing the more recalcitrant polyethylene-based films, but their complete biodegradation in field conditions is questionable. Plastic weathering, fragmentation, microbial proliferation, and production of polymer-degrading exoenzymes are needed processes for a complete degradation of plastic residues. But these physicochemical and biological processes do not always jointly happen because of unpredictable environmental conditions. Recent studies suggest that earthworms, particularly anecic and endogeic species, may facilitate plastic biodegradation directly and indirectly via their strong impact on soil microbial properties and the resulting intense soil bioturbation. The scope of this perspective paper is to stimulate the development of earthworm-based strategies for reducing microplastic-effects in soil functioning. We introduce the current state of knowledge on microplastic-earthworm interaction and describe the behavior- and gastrointestinal-associated mechanisms whereby earthworms may contribute to polymer biodegradation. Because plastic mulching technology may threat soil quality, we propose a conceptual model using earthworms to reduce side-effects (i.e., microplastic accumulation in soil and quick nutrient depletion) derived from this agricultural system.