Sediment-specific microbial nitrogen cycling disruption by fluoroalkylether substitutes: HFPO-DA and PF4OPeA exert...

Fluoroalkylether substances (ether-PFASs), emerging substitutes for legacy PFASs, exhibit increasing marine sediment contamination comparable to traditional PFASs, yet their specific impacts on microbial nitrogen cycling remain poorly understood. This study reveals compound-specific mechanisms by which two ether-PFASs (Heptafluoropropylene oxide dimer acid (HFPO-DA) and Perfluoro (3-methoxy) propionic acid (PF4OPeA)) disrupt nitrogen transformations in three Pacific sediments across environmental concentrations (0.01-100 μg/g). HFPO-DA significantly altered nitrification rates in sediment- and concentration-dependent manners while consistently promoting nitrite reductase (NiR) activity by 0.5-20.5 % across all sediments. Conversely, PF4OPeA primarily stimulated nitrification but exerted divergent effects on NiR that were critically dependent on the sediment habitat, ranging from promotion to universal inhibition. Structural equation modeling (SEM) identified fundamentally distinct pathways: HFPO-DA directly regulated nitrification via sediment-modulated ammonia-oxidizing bacteria (AOB) amoA gene abundance and denitrification through nirS/nirK genes. In contrast, PF4OPeA modulated nitrification by first altering bacterial α-diversity, which subsequently influenced AOB amoA, while its denitrification effects propagated through a cascade involving sediment properties, α-diversity, nirS, and NiR activity (p < 0.05). These results establish that ether-PFASs subvert nitrogen cycling via divergent mechanisms: HFPO-DA targets functional genes directly, whereas PF4OPeA acts through microbial community restructuring, with sediment properties dictating ecotoxicity and critically mediating both outcomes. This work thereby provides a critical basis for ecological risk assessment of PFAS alternatives in marine environments.