Plastic carbon in urban composts estimated by a novel quantification method based on Rock-Eval® thermal analysis : Scenario of accumulation in amended soils

Abstract

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.