Distribution and characteristics of Microplastics in leachate and underneath soil of two informal landfills

Microplastics (MPs), an emerging pollutant, have garnered global attention as significant environmental concerns. Landfills are the major sources of MPs. However, research on the distribution and characteristics of MPs in leachate and underneath soil of informal landfills remains limited. This study investigated the abundance, polymer type, size, and morphology of MPs in 6 leachate samples and 18 underneath soil samples at different depths from two informal landfills. The ranges of MPs abundance in leachate and underneath soil from landfills were 4,010-33,213 items/Land 592-870 to 47,819 items/kg, related to the landfilled waste composition. MPs size between 20 and 100 µm accounted for the highest proportion (70 %). The fragmentation coefficient α in the underneath soil was higher than that in the leachate, indicating smaller MPs were more likely to migrate into underneath soil after filtration. The fibrous MPs proportion was below 22 %, while the fragmented MPs was more than 78 %. Large fibrous MPs were detected in the underneath soil in landfill A. Polyethylene Terephthalate (PET), Polyurethane (PU) and Polystyrene (PS) were the predominant MPs polymers types in leachate and underneath soil. Polypropylene (PP) was primarily concentrated in the upper and middle underneath soil layers, and Polyurethane (PU) was predominantly in the middle and lower layers. Principal component analysis (PCA) results indicated that geographical factors significantly influenced the distribution and characteristics of MPs. This study revealed the distribution of MPs in leachate and underneath soil at different depths, providing a valuable reference for the risk assessment of MPs pollution.