Construction and verification of soil heavy metal establishment identification method based on dual-threshold of...

Pollutants from industrial emissions and traffic accumulate in urban soils as road dust, carrying heavy metals (HMs) posing ecological and health risks. Magnetic susceptibility (MS), sensitive to ferromagnetic minerals, enables rapid HM contamination assessment. This study developed the Modified Dual-Threshold MS Evaluation Plot for Soil Contamination (M-Plot) using χ_lf and χ_fd% indices. Representative Chinese soils were amended with road dust to study MS relationships with HM concentrations (Pb, Zn, Cu, Cd). Simulations and multi-regional validation support the M-Plot criterion (χ_fd% < 3 % and χ_lf > 50 × 10⁻⁸ m³ kg⁻¹). The accuracy reaches 85 %, improving on Wang's (2000) criterion by 15 %. This enhances early-stage pollution detection sensitivity. Soil parent material characteristics (e.g., magnetic mineral composition) are key controlling factors. Red and purple soils show the strongest response due to low magnetic background. This provides an efficient screening tool for early-stage urban soil pollution. However, soils with high background magnetism require supplementary geochemical data. Future research should quantify soil-specific HM (e.g., Cd, Cu) adsorption, build multi-source tracing models addressing heterogeneity, incorporate bioavailability (e.g., plant uptake) into risk evaluation, and perform aging experiments with field validation to understand pollutant aging and multi-source impacts on MS-HM mechanisms.