Deciphering the Environmental Fate of Halogenated Organic Compounds in Cold Seep Sediments: Insights from Non-targeted Analysis and Metagenomics across Vertical Redox Gradients

Halogenated organic compounds (HOCs) are pervasive in marine environments, yet their molecular diversity, vertical distribution, and fate in deep-sea ecosystems remain largely uncharted. Here, we integrated non-targeted analysis, geochemical profiling, and metagenomics to systematically analyze a 500-cm sediment core from the Haima deep-sea cold seep, deciphering these key aspects and their controlling factors. Non-targeted analysis identified 669 HOCs (at molecular formula level), predominantly of marine origin with saturated structures. The highest HOC diversity was found in the oxic/suboxic (OS) zone, where 73.4% of the frequently detected HOCs reached their peak abundance. Concurrently, a marked decrease in organochlorines was observed at the OS–suboxic/anoxic (SA) interface, followed by level stabilization below this transition, suggesting regulation by abrupt redox shifts. Correlation analyses revealed co-regulation of HOC distribution by geochemical (e.g., depth, pH, and SO 4 2- ) and microbial (e.g., reductive and hydrolytic dehalogenases) factors. Metagenomics combined with redundancy analysis further demonstrated significant interactions between HOCs and dehalogenating microbial community along the vertical profile. In summary, this study provided an integrated perspective on the biogeochemical cycling of HOCs in the deep-sea cold seep, linking their removal at redox boundaries, long-term burial, and spatial organization to underlying microbial and geochemical drivers.