Direct Current Electric Field Modulation of Mass Transport in Soils: A Comprehensive Review

Mass transport within the Earth critical zone is fundamental to sustaining ecosystem functions. This process is governed by a complex interplay of natural factors, including soil, microbial, and chemical properties. However, mass transport is often impeded by microscale barriers in low-permeability soils, restricting the mobility of microorganisms and compounds, thereby limiting essential processes from biogeochemical cycling to resource recovery. Among various intervention strategies, the application of a direct current electric field induces electrokinetic phenomena electromigration (EM), electroosmosis (EO), and electrophoresis (EP), that act in concert to mobilize pore fluids and enhance the co-transport of compounds and biodegrading microbes. This review synthesizes how electrokinetic fields enhance mass transport in soils. It systematically resolves the electrokinetic-driven interactions within the microbe-matrixcompound triad, analyzing the distinct electrokinetic effects on bacterial deposition and transport at interfaces, as well as on compound sorption and desorption. We elucidate how the interplay of electric and chemical mechanisms governs the transport dynamics, with EO serving as a universal driver, while EM and EP preferentially facilitate ion and bacterial transport in nano-and micro-pores, respectively. Furthermore, the synergistic effect of superimposed thermal fields is examined for its role in tuning key physical properties to further improve delivery efficiency. We provide perspectives on future research priorities, which include targeted microbiome engineering and in situ sustainable mining applications. This synthesis aims to provide a systematic strategy for deploying electrokinetic interventions to overcome transport barriers and enhance ecosystem services in both natural and engineered environments.