Sediment texture induces Fe-S redox zonation and alters microbial assemblages affecting natural attenuation of BDE-47...

This study investigated the attenuation of 2,2',4,4'-tetrabromo-diphenyl ether (BDE-47) in laboratory-scale upflow columns simulating hyporheic zones (HZ) with a focus on how sediment texture governs Fe-S redox zonation, microbial community assembly, and debromination dynamics. A ∼10 % difference in silt-clay content between two artificial sediments was identified as the key factor driving divergent microbial niches and degradation pathways. The coarser column (SS) promoted rapid initial BDE-47 attenuation (weeks 5-9) via enhanced iron reduction, however, the finer column (SCS) achieved an accelerated late-stage efficiency (3.42 µg week^-1, 12.7-fold higher than SS) during weeks 9-12, driven by intensified sulfate reduction and most pronounced at the 25 cm middle layer. Conserved aerobic-anaerobic co-abundance networks supporting facultative dehalorespiration through fermentative syntropy and Fe-S cycling, predominantly mediated by Desulfuromonas, were selectively shaped by sediment texture, thereby regulating the efficiency and timing of PBDE biodegradation. Notably, a Zoogloea-Flavobacterium-Legionella triangle bridging module in SS was identified as an indirect biofilm-mediated facilitation mechanism for PBDE debromination. This study advances our understanding of microbial debromination in heterogenous porous media, thereby providing a physico-ecological mechanistic basis for engineering HZ barrier systems against halogenated persistent organic pollutants like PBDEs.