Multidimensional characterization of microplastic pollution in subtropical urban soils: Combining geospatial analysis and polymer risk indexing

Microplastics (MPs) in urban soils of Macao, a high-density coastal city, were investigated to assess distribution patterns and ecological risks under anthropogenic pressures. MPs were extracted via density separation and H2O2 digestion, characterized using stereomicroscopy and μ-FTIR. Results showed significant accumulation (1.3 × 10³–2.6 × 104 items/kg; mean: 1.1 × 104 items/kg), dominated by fibers (49.4 %) and transparent particles (32.3 %). Polyethylene terephthalate (PET, 37.6 %) and polypropylene (PP, 18.3 %) were predominant, with 20–500 μm fragments as the prevalent size. MP abundance varied significantly across land uses, with traffic and commercial/residential areas exceeding natural green areas (p < 0.05). Population density positively correlated with MP levels (p < 0.01). Traffic activities influenced MP characteristics, while soil conductivity and organic matter correlated with MP abundance. MP shape and size exhibited variable relationships with soil particle content. Risk assessments using pollution load index (PLI), polymer hazard index (PHl), and potential ecological risk index (PERI) revealed substantial ecological threats, with PHl and PERI classifying sites into risk categories IV and V, respectively, driven by high hazard polymers (PAN, PVC). Hierarchical clustering for source analysis of MPs, and geospatial analysis based on the Inverse Distance Weighting (IDW) interpolation method, combined with the abundance of MPs and PERI, to predict the distribution map of soil MP pollution risk in Macao. This study provides critical baseline data on urban MP dynamics in coastal cities. Highlighting the need for targeted mitigation of high-risk polymers in regions with similar anthropogenic stressors.