Iron–nitrogen synergistic mechanisms governing arsenic speciation and mobility: a critical review of interfacial reactions and microbial redox transformations

Abstract As a pivotal component of Earth's geochemical cycles, the nitrogen (N) cycle is exceptionally complex and crucial for maintaining environmental N dynamics. As a highly active metal, iron (Fe) is closely associated with the N cycle through biological and abiotic pathways. Notably, these interactions frequently mediate concurrent transformations of co-existing contaminants, particularly arsenic (As). Recent advances have elucidated three key Fe–N coupled microbial pathways: NO 3 − -reduction driven iron oxidation (NDFO), Fe-mediated dissimilatory NO 3 − reduction to ammonium (NH 4 + ) (Fe-DNRA), and anaerobic NH 4 + oxidation coupled with Fe(III) reduction (Feammox). These mechanisms demonstrate promising potential for As pollution mitigation in engineered systems. This review systematically synthesizes current understanding of Fe–N-As triad interactions, with particular focus on (1) mechanistic insights into Fe–N coupled biogeochemical pathways, (2) spatial–temporal patterns of As transformation mediated by these processes in critical environmental matrices (paddy soils and groundwater systems), and (3) practical applications in As remediation technologies. Furthermore, we propose novel conceptual frameworks elucidating the complex interplay within Fe–N-As ternary systems, providing critical insights for developing bioremediation strategies targeting As-contaminated environments. Graphical abstract