Effects of BDE-47 injection on vertical redox zonation and microbial community assemblage in capped sediment columns

Polybrominated diphenyl ethers (PBDEs) are of significant interest in ecological risk assessment and bioremediation in sediments. However, their impact on microbial diversity and activity in capped lake sediments remains unclear, despite the widespread use of capping in lake management. In this study, two series of sediment columns were established to examine vertical redox zonation at 2-cm intervals from 2 to 16 cm and evaluate the impact of artificially injected PBDEs on microbial communities during a 60-day capping period. Variations in redox indicators, including nitrate, sulfate, total dissolved iron, and total dissolved manganese in porewater, showed that the capping layer (1 cm, d = 75 μm) increased the redox potential of subsurface sediments. BDE-47 was primarily concentrated in the injection layer (4-6 cm), but over time, it exhibited upward migration (0.4-0.7 cm) and a broader distribution range (0.5-1.0 cm), with no consistent decrease in the total BDE-47 mass. Microbial α-diversity declined, whereas microbial network analysis revealed increased connectivity and enhanced cooperation within communities in the BDE group. Notably, negative correlations between microbial taxa and iron exclusively in the BDE group, suggesting that BDE-47 counteracted capping-induced iron reduction. In contrast, sulfate showed an opposite trend with iron between the BDE and noBDE groups. Methanolinea [Euryarchaeota] and certain co-metabolizing dechlorinating bacteria, such as Flavobacterium dominated in the capping layer, were correlated to BDE-47. These findings provide the first evidence of redox-regulated natural attenuation of PBDEs in capped lake sediments, shedding light on their environmental impact and guiding sediment management strategies.