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Microplastic pollution during organic compost production: Occurrence and ecological risks
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Turning food and yard waste into compost is supposed to be eco-friendly, but this study found that the composting process actually *increases* tiny plastic particles (microplastics) more than three-fold — from trash input to finished compost. Since this compost often ends up on farms and gardens, it could be a hidden way plastics get into our soil, crops, and eventually our food supply, raising concerns that need better filtering solutions before compost is widely used.
The conversion of the organic fraction of municipal solid waste into compost via mechanical and biological treatments is a widely practiced and cost-effective waste management approach. However, the impact of these processes on the characteristics of microplastics (MPs) remains poorly understood. This study investigated the levels and characteristics of MPs during composting and in the final products, and assessed the associated ecological risks. 54 samples were collected from different stages of the composting process, from incoming waste (IW) to refined compost (RC). After pre-treatment, stereo microscopy was used for preliminary identification, followed by Fourier-transform infrared spectroscopy (FTIR) for polymer identification of particles > 1 mm and micro-Raman spectroscopy for smaller MPs. The average microplastic concentration increased from 22,800 N/kg in IW to 75,928 N/kg in RC. Fibers were the most abundant type of microplastic throughout composting, while black MPs dominated (accounting for 50% of all particles). In IW, polyethylene (PE) and polyethylene terephthalate (PET) were the main polymers, whereas in RC, polystyrene (PS) and PET were most prevalent. Ecological risk assessment revealed a polymer hazard index (PHI) of 491.7 (risk level III) and a pollution load index (PLI) of 59, indicating a level IV (extremely high) category based on PHI and PLI classification schemes. These findings indicate that microplastic abundance increases during the composting process, highlighting the need for effective pre-treatment strategies to reduce plastics and microplastics in the feedstock and minimize their release into the environment.
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Researchers found that the composting process actually increases microplastic contamination rather than reducing it, breaking larger plastic pieces into smaller, more numerous particles. Even when visible plastics were sorted out before composting, the final compost still contained thousands of microplastic particles per kilogram. Since compost is widely applied to farm fields, this study reveals an overlooked pathway for microplastics to enter agricultural soil and potentially the food supply.
Plastics and other extraneous matter in municipal solid waste compost: A systematic review of sources, occurrence, implications, and fate in amended soils
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Researchers reviewed contamination in municipal compost made from household organic waste, finding plastics are the most prevalent pollutant — with some batches containing enough plastic to deposit over 500 kg per hectare of farmland each year. Repeated use of contaminated compost builds up microplastics in soil, threatening soil health and potentially moving plastic particles into crops and food.
Plastic contamination of soil: is compost the source?
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Researchers assessed compost as a source of plastic contamination in agricultural soils, finding detectable levels of microplastics in commercial composts that are subsequently applied to farmland. This study identifies composting of plastic-contaminated organic waste as an underappreciated pathway for microplastic introduction into agroecosystems.
Microplastics identification and quantification in the composted Organic Fraction of Municipal Solid Waste
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Researchers quantified microplastics in composted organic municipal solid waste from five facilities, finding contamination levels that raise concerns about compost quality and the potential transfer of microplastics to agricultural soils through organic waste recycling.
A systematic review of the occurrence of microplastics in compost: Understanding the abundance, sources, characteristics and ecological risk
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Researchers reviewed 19 global studies and found microplastics in virtually all types of compost — including those made from animal manure, sewage sludge, and municipal waste — with concentrations reaching up to 288,000 particles per kilogram in some samples. Since compost is widely applied to farmland, these findings highlight a significant but overlooked pathway for microplastics to enter soils and the food chain.
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