A multiscale perspective on the occurrence, transport mechanisms, and molecular interactions of heavy metals in...

Heavy metals pollution arising from human activities and industrial production continues to threaten the environment and public health, yet integrative, cross-scale elucidations that bridge field monitoring, mesoscopic transport, and molecular mechanisms remain limited. This review compiles 415 datasets from over 300 contaminated sites across industrial, e-waste, and mining regions worldwide to analyze the distribution, co-occurrence patterns, and migration behavior of heavy metal in soils. Globally, lead (Pb), copper (Cu), zinc (Zn), and cadmium (Cd) are the most detected contaminants; Pb shows a detection rate as high as 87.59%. E-waste sites exhibit higher detection rates for multiple metals (100% detection for Pb), whereas mining sites display the most extreme enrichment, with Zn concentrations up to 131365 mg/kg. Pearson correlation analysis reveals site-type-dependent co-occurrence signatures, for example, Ni (nickel)-Cr (chromium)-Cu in industrial sites and Pb-Cu in e-waste sites, with correlation coefficient "r" up to 0.9. Coupled-process models incorporating advection, diffusion, dispersion, and adsorption dominate current numerical studies, while biogeochemical transformations remain insufficiently represented. Diffusion coefficients generally increase under soil acidic conditions, and amphoteric Pb exhibits pronounced pH-dependent mobility. A thematic synthesis of molecular dynamics studies (1985-2025) highlights growing focus on adsorption and surface complexation at mineral-water interfaces. The exceptionally strong interactions between Pb and soil minerals or organic matter at molecular scales provide a mechanistic explanation for why Pb exhibits the highest detection frequency and concentrations at field scale. By adopting a multi-scale perspective, this review provides data support and mechanistic foundations for risk assessment, spatial characterization, elucidation of transport mechanisms, and the design of remediation at contaminated sites.