Microplastic diversity, risks and soil impacts: A multi-metric assessment across land-use systems

Soil microplastic (MP) pollution is an emerging concern, but its spatial patterns, ecological risks and impacts remain poorly understood. This study aimed to assess MP abundance, diversity, risks and influence on soil properties across seven land use land cover (LULC) types in the Brahmaputra Valley, integrating microscopy, spectroscopy-based MP identification, ecological diversity indices and APCS-MLR modelling. Fifteen composite topsoil samples per LULC were collected and analysed. MP concentrations ranged from 5 to 57 particles kg⁻¹ , peaking in built areas (38 ± 8) with high polymer diversity (MDII = 0.72), while forest soils exhibited the highest polymer hazard score (PHI = 5706) due to high-risk polymethylmethacrylate MPs, despite lower MP abundance. High-density polyethylene, polybutylene and polyethylene terephthalate accounted for over 56 % of all MPs. Black MPs were most prevalent, and fibres and fragments were dominant shapes. Diversity indices indicated higher polymer richness in urban and agricultural soils, suggesting heterogeneous input sources. PCA and NMDS analyses indicated that polymer composition controls ecological risks and influences soil properties such as porosity, bulk density and SOC. APCS-MLR identified that polyethylene, polystyrene and fragment-shaped MPs had positive impacts on the tested soil parameters, while polyvinyl chloride, polyacetonitrile based MPs and fibre-shaped MPs had negative impacts on soil properties. This study highlights that LULC influences both the quantity and characteristics of terrestrial MPs, with potential implications for soil function and pollutant transport. The findings underscore the need for polymer-specific monitoring and targeted mitigation in the terrestrial environment and offer a framework for land-based pollution studies.