Comparative fate and risk of microplastics in sanitary landfills versus open dumping sites: A multidimensional...

Municipal solid waste (MSW) landfills are critical terrestrial reservoirs of microplastics (MPs), yet how disposal methodology governs MP fate remains poorly constrained, hindering accurate risk assessment and management. Here, we systematically compared MP pollution between an engineered sanitary landfill (SL) and an open dumping site (OD) in East China through field investigation and laboratory simulation. We analyzed spatial distribution, physicochemical characteristics, and release potential of MPs, and developed a novel Index (MDAI) that integrates soil species sensitivity distribution (SSD), abundance, size, shape, and polymer hazard to assess ecological risk. Results revealed that MP abundance in SL (5340-12,670 particles/kg soil) markedly exceeded that in OD (2100-5620 particles/kg soil), with SL exhibiting a distinct vertical accumulation gradient absent in OD. MP abundance on plastic waste were substantially higher, reaching 29,740 particles/kg plastic on deeply buried SL plastics. MPs in SL were predominantly small-sized fragments and films dominated by polypropylene, whereas OD contained more fibers and medium-sized fragments dominated by polyethylene. Surrounding soils of the OD showed higher MP levels and extremely high potential ecological risk (PERI), whereas those of the SL exhibited only Level III risk. Plastic waste from both sites demonstrated ongoing MP release potential, most pronounced for deeply buried SL waste. The MDAI indicated a higher comprehensive risk within SL (Level III) versus moderate but spatially dispersed risk around OD (Level II). This spatial disparity highlights distinct management priorities: for SL, ensuring long-term containment to prevent release of internally accumulated MPs; for OD, implementing immediate source control and migration barriers to limit off-site dispersion. This study provides a critical, multidimensional framework for assessing and managing MP pollution from these predominant waste disposal pathways.