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Plastic carbon in urban composts estimated by a novel quantification method based on Rock-Eval® thermal analysis: Scenario of accumulation in amended soils
Original title: Plastic carbon in urban composts estimated by a novel quantification method based on Rock-Eval® thermal analysis : Scenario of accumulation in amended soils
Summary
Scientists developed a new way to measure how much plastic ends up in soil when compost is used as fertilizer on farms. After testing compost applied over 21 years, they found that compost made from municipal trash left nearly 5% of the soil's carbon in the form of plastic — far more than compost made from food scraps or yard waste, which left less than 1.5%. This suggests that the type of compost you use matters: composts made from cleaner, more sorted materials may be a better choice for reducing microplastic buildup in the soil that grows our food.
Soil microplastic pollution is an increasing concern for agricultural soils, threatening soil functions and human health. Compost, used as green fertilizer, introduces microplastics into agricultural soils. Yet, quantifying the microplastics in compost and soil is challenging. We developed a method to estimate the microplastic content of composts derived from different organic waste, using Rock-Eval® analysis combined with the index of residual organic matter. We estimated the microplastic content of compost samples applied in a long-term field experiment and deduced the plastic-derived soil organic carbon pool. Our results showed that, after compost addition from 1998 to 2019, urban compost derived from biowaste and green-waste composted with sewage sludge stored respectively 16% and 24% more carbon in the soil than urban compost derived from municipal solid waste. Furthermore, 4.7% of soil organic carbon was present in the form of plastic-carbon after 21 years of municipal solid waste compost use, while it represented only 1.4% and 0.3% in soils amended with biowaste and green-waste composted with sewage sludge composts respectively.