Integrated spatial assessment, transformation, and risk evaluation of microplastics in tropical municipal landfills

Municipal solid waste landfills (MSWLs) are highly complex environmental systems in which microplastics (MPs) undergo continuous transformation; however, effective depth-wise assessment techniques for landfill environments remain limited. This research used an integrated analytical and risk-assessment framework to investigate the distribution, transformation, and environmental risks associated with MPs in a sanitary landfill in India. Depth-dependent sampling (0-16 m at 1 m intervals) of soil and solid waste was conducted, followed by wet peroxide oxidation, density separation, and microscopic quantification. This was then complemented by polymer identification and surface characterisation through FTIR and SEM-EDS. MP concentrations ranging from 5500 ± 3.54 to 25,200 ± 19.79 particles/kg (dry weight), including 12 distinct polymer types. SEM-EDS analysis showed continuous physical and chemical transformations correlated with increasing landfill depth, including surface cracking, increased roughness, and changes in elemental composition. Fragment-shaped MPs increased from 31.24% to 48.13%, whereas particles smaller than 500 µm decreased from 36.46% to 28.92%, suggesting size-selective weathering mechanisms. The carbon content decreased from 42.7% to 26.9%, concurrently with a decrease in the C/O ratio from 1.01 to 0.76, indicating oxidative polymer degradation within the landfill environment. Integrated pollution and ecological risk indicators indicated spatial fluctuations in MP contamination levels, with risk assessments ranging from low to high across different landfill strata. This framework offers a systematic methodology for assessing the spatial patterns of MPs within landfill systems and has practical significance for landfill monitoring, risk prioritisation, and the development of pollution control strategies.