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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.
Plastic contamination is a major environmental topic, however, only little knowledge exists about plastic contamination of agroecosystems. Especially the prevalence of plastic in soil and potential entry paths remain largely unknown. Consequently, this study aims at evaluating to what degree compost application is a source of plastic for soil. To do so, we analyzed plastic in 8 different municipal and commercial composts and in topsoil (0-30 cm) of a 12-year compost fertilizer trial with 0, 5, 10 and 20 t compost per hectare. After method testing and adjustment (yielding 76-100% recovery of spiked plastic particles), plastic was analyzed via density separation (ZnCl2) and light microscopy. We found 12±8 to 46±8 plastic items kg-1 compost; concentrations of plastic items > 5 mm were highly variable and ranged between 0.04±0.08 to 1.35±0.53 g kg-1 compost. In contrast to sewage sludge, which contains mostly fibers, in compost particles were dominant. In soil we found 0 to 66±8.5 plastic items kg-1 soil, with highest plastic concentrations in variants with highest compost application, i.e. soils with compost application had 2 to 2.5 higher plastic concentrations than control variants. However, we also could detect additional plastic sources as fields on the border of the trial (near a road) had 3 times higher plastic concentrations than inner fields, leading to a plastic contamination of up to 23 items kg-1. Consequently, we could confirm compost application as an entry path for plastic into soil, leading to a twofold increased plastic contamination of agricultural soil. The determined plastic input via compost might be a minimum estimate since small plastic items like nanoplastics were not included, which warrants further attention.
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This study examined microplastic pollution in soils that had received long-term amendments of urban compost, finding significant plastic contamination from compost application. The results highlight that composting can be a pathway for microplastics to enter agricultural soils.
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Researchers analyzed commercially available compost products to determine how much microplastic contamination they contain. They found microplastics in all tested composts, with fibers and fragments being the most common forms, primarily made of polyethylene and polypropylene. The findings raise concerns that applying commercial compost to agricultural land may be an overlooked pathway for introducing microplastics into soil.
Microplastic contamination of soil: Are input pathways by compost overridden by littering?
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Researchers investigated whether compost application is a major pathway for microplastic contamination of agricultural soil using a long-term fertilizer trial. The study found that while compost does contribute microplastics, the levels detected were relatively low compared to microplastics from general littering, suggesting that environmental littering may be a more significant source of soil microplastic contamination than composting.
Biowaste Compost Amendment is a Source of Microplastic Pollution in Agricultural Soils
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Researchers found microplastics in Indian agricultural soils amended with biowaste compost, with concentrations increasing in proportion to years of compost application. Polypropylene was the dominant polymer type, showing that compost amendments can introduce microplastics into farmland soils.
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.
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