Mechanisms of migration and transformation of persistent organic pollutants in soil under synergistic actions of multiple factors

Persistent organic pollutants (POPs) in soils are governed by coupled migration and transformation processes rather than by isolated responses to single environmental variables. This review focuses on representative legacy and regulated hydrophobic POPs, including polycyclic aromatic hydrocarbons (PAHs), organochlorine pesticides, DDT and its major transformation products, and polychlorinated biphenyls. We synthesize how pH, soil organic matter (SOM) and soil organic carbon, salinity, mineral composition, texture, temperature, moisture, oxygen availability, microbial communities, extracellular and intracellular enzymes, soil fauna, and plants jointly regulate sorption–desorption, aging, volatilization, leaching, colloid-facilitated transport, redox transformation, biodegradation, uptake, and trophic transfer. Across pollutant classes, hydrophobic partitioning into organic-carbon domains and mineral–organic complexes generally limits short-term aqueous mobility, whereas low-carbon sandy soils, dissolved- or colloidal-organic-matter transport, salinity-dependent interfacial changes, preferential flow during wet–dry or freeze–thaw cycles, and temperature-enhanced volatilization can increase cross-interface transfer. Transformation is pathway specific: aerobic monooxygenase, dioxygenase, and peroxidase systems mainly promote PAH activation and ring cleavage, whereas anoxic organohalide-respiring communities and reductive dehalogenases favor sequential dechlorination of highly chlorinated POPs. The relative importance of these mechanisms changes with pollutant loading, aging, co-contaminants, water connectivity, electron-donor availability, and climatic disturbance. The synthesis identifies three priority gaps: quantitative relationships linking distribution coefficient (Kd)/organic carbon-water partition coefficient (KOC), desorption hysteresis, freely dissolved concentrations, degradation rate constants, and environmental thresholds; insufficient explanation of nonlinear temperature–moisture, pH–redox, SOM–microbe, and co-contaminant interactions; and limited translation of molecular, multi-omics, and laboratory evidence into field-scale prediction and remediation design. A mechanism-based framework is proposed to connect soil-phase distribution with retention, transport, transformation, exposure, and risk under heterogeneous soil and climate-change scenarios.