Microplastics and impurities in digestates and compost: A comparative study of waste-derived soil amendments.
Newrick BA, Laca A, González-LaFuente JM, Laca A
Soil Health
Compost you spread on vegetable beds or buy from a garden center may be quietly delivering a dose of plastic fibers and fragments into the soil where your food grows—and this study shows the source of that compost makes a dramatic difference in how much plastic comes with it.
Scientists tested five different types of compost and digestate—materials made from food scraps, green waste, sewage sludge, and mixed trash—to see how much plastic had snuck in. Every single material contained tiny plastic pieces, mostly fibers, thin films, and fragments, made from everyday plastics like plastic bags and bottles. The compost made from carefully sorted household food waste had the least plastic, while the material made from mixed garbage had by far the most, showing that sorting your recycling and food waste at home really does matter.
Key Findings
Plastic concentrations ranged from 0.03% dry weight in green waste/manure compost to 2.44% in bio-stabilised mixed municipal waste—an 80-fold difference driven by waste source and sorting quality.
Microplastics smaller than 2 mm made up 30–65% of total plastics found across all materials, with fibers, films, and fragments as the dominant forms; polyethylene, polypropylene, PET, and polyester were most common.
Only the bio-stabilised mixed municipal waste product exceeded legal impurity limits, while all five materials stayed within legal gravel/stone thresholds—but none were microplastic-free.
chevron_right Technical Summary
Researchers tested five types of organic soil amendments—composts and digestates from different waste sources—and found microplastics in all of them, with the worst offender (bio-stabilised mixed municipal waste) far exceeding legal impurity limits. The findings underscore that how waste is collected and sorted upstream directly determines how much plastic ends up in your soil.
Abstract Preview
Organic waste treatment plays a key role in sustainability by reducing greenhouse gases, minimizing landfill, and recycling nutrients. However, microplastics (MPs) are increasingly reported in orga...
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