Arsenic dynamics in physicochemically heterogeneous aerobic aquifers mediated by redox capacity

Aquifers are typically heterogeneous in both structure, which appears as variations in hydraulic conductivity (K), and chemistry, which is governed by the spatial distribution of electron accepting and donating capacity (EAC and EDC). Arsenic (As), a highly toxic and strongly mobile groundwater pollutant, requires a comprehensive understanding of its transport and transformation behaviour—especially during early remediation stages. Studying the dynamics of As is challenging in highly heterogeneous aquifers, where both flow paths (controlled by structure) and reaction rates (influenced by chemistry) play complex roles. For the first time, the redox capacity is used to characterize biogeochemical reaction processes. Static batch experiments confirmed that the redox capacity-mediated reaction kinetics framework effectively captured electron transfer from various active components. Furthermore, the validated reaction kinetics was applied to a two-dimensional radial model to examine how As transports and transforms in the aquifer matrix and lens structures. The study also quantified the relationship between physicochemical heterogeneity and the breakthrough curves (BTCs) of As. The research offered a new framework for understanding arsenic dynamics from an electron-transfer-based perspective.