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Microplastics in Composts, Digestates and Food Wastes: A Review
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Researchers reviewed microplastic contamination in composts, digestates, and food wastes, finding that plastic packaging mixed into food waste streams may inadvertently introduce microplastics into agricultural soils during composting or anaerobic digestion. The authors highlight critical research gaps and call for harmonized methods to better assess this potential pathway of soil microplastic contamination.
Diverting food waste from landfills to composting or anaerobic digestion can reduce greenhouse gas emissions, enable the recovery of energy in usable forms, and create nutrient-rich soil amendments. However, many food waste streams are mixed with plastic packaging, raising concerns that food waste-derived composts and digestates may inadvertently introduce microplastics into agricultural soils. Research on the occurrence of microplastics in food waste-derived soil amendments is in an early phase and the relative importance of this potential pathway of microplastics to agricultural soils needs further clarification. In this paper, we review what is known and what is not known about the abundance of microplastics in composts, digestates and food wastes and their effects on agricultural soils. Additionally, we highlight future research needs and suggest ways to harmonize microplastic abundance and ecotoxicity studies with the design of related policies.
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Microplastics in MSW-derived compost: release rate, characteristics, ecological risks, and mitigation strategies for sustainable agriculture
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Compost made from household trash often contains tiny plastic bits called microplastics, and surprisingly, the compost from industrial facilities had even more plastic contamination than the raw waste it started from. Since this compost gets spread on farm fields, these plastic fragments can build up in the soil where our food grows. The good news: simply sorting out plastic from food/organic waste before composting (rather than mixing everything together) dramatically cuts down on this contamination, suggesting better recycling habits at home and in waste facilities could help keep microplastics out of our agricultural system.
The Efficiency of Different Digestion and Separation Methods for Extracting Microplastics in Typical Organic Solid Waste
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This study compared seven digestion protocols and three separation methods for extracting microplastics from organic solid waste such as compost and biogas residues, identifying 30% hydrogen peroxide digestion followed by two-stage density separation as optimal with over 86% recovery. Standardized extraction methods are critical for generating comparable data on microplastic contamination in agricultural inputs that ultimately transfer plastic particles into soils.
Microplastic Pollution in Compost Derived from Mixed Municipal Waste in Kermanshah City: Abundance, Characteristics, and Ecological Risk Evaluation
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Researchers found that compost made from mixed municipal solid waste in Kermanshah, Iran, was universally contaminated with microplastics at an average of 2,160 particles per kilogram — translating to an estimated 118 million microplastics added to each hectare of farmland annually — posing medium to high ecological risk and highlighting compost as a significant pathway for microplastic entry into agricultural soils.
Effect of Ventilation Modes on Microplastic Flow During Perishable Waste Composting
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Researchers investigated how four ventilation methods affect microplastic distribution during perishable waste composting, finding that composting reduced extractable MPs in the solid product by 73–84%, with most MPs migrating to leachate and composting time being the strongest influencing factor. This matters because MP migration into leachate means contaminated liquid can carry plastics into soils and waterways if not properly managed during this widely used organic waste treatment process.
Urban dimension of microplastics in municipal solid waste compost within an emerging eastern Indian city
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Researchers mapped microplastic contamination across five socioeconomically distinct composting stations in an eastern Indian city, finding abundances from 1,111 to 2,111 items/kg with polyethylene dominant and Polymer Hazard Index scores indicating the highest risk category at most sites. The study reveals that urban composting—intended to recycle organic waste into soil amendment—is inadvertently distributing hazardous microplastics into agricultural and residential soils across different socioeconomic zones.
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When a large batch of papers lands in the Atlas, we read through it and send a short write-up of what stood out.