Spatial Distribution Characteristics of Typical Contaminants in Municipal Solid Waste Landfills under Water-Soil Interactions in Alluvial-Diluvial Strata

• • Groundwater at the landfill site exhibited severe contamination (PI > 3), with maximum exceedance multiples of 36 for total bacterial count, 9.5 for ammonia nitrogen, and 8 for total coliforms, indicating a direct leachate impact and necessitating urgent remediation. • • Soil concentrations of Cu, Pb, Cd, Ni, Hg, and As were all below GB 36600—2018 Class II screening values, with Nemerow pollution index (PI < 0.7) and potential ecological risk index (RI < 150) confirming overall soil safety, yet spatial heterogeneity (coefficient of variation > 36%) suggests localized hotspots. • • Soil DOM was dominated by humic-like (22.9%–34.9%) and fulvic-like (22.4%–27.5%) substances, with fluorescence intensity decaying exponentially with depth, indicating vertical transport and transformation of organic matter. • • Cadmium exhibited high mobility risk: active forms (exchangeable + Fe/Mn oxide-bound) accounted for 72.6%–86.7%, whereas Cu, Pb, As, Hg, and Ni were predominantly in residual fractions (52.33%–90.32%), highlighting Cd as a priority control target.