PFASs pose a threat to deep-sea cold seeps

Inputs of per- and polyfluoroalkyl substances (PFASs) threaten deep-sea cold seep ecosystems, yet their environmental behavior and risks remain poorly understood. We report a comprehensive investigation of 30 PFASs in seawater and sediment from South China Sea cold seeps. Emerging PFASs, notably 2,3,3,3-tetrafluoro-2-(1,1,2,2,3,3,3-heptafluoropropoxy) propanoic acid (hexafluoropropylene oxide dimer acid [HFPO-DA]) and sodium 1 H ,1 H ,2 H ,2 H -perfluoro-1-octanesulfonate (6:2 FTS), are widely detected. Seawater (0.75–3.52 ng/L) and sediment (0.45–2.55 ng/g dw) levels indicate moderate contamination, exceeding pristine open baselines but remaining below coastal impacts. Crucially, downward-decreasing sediment profiles are significantly disrupted by active methane seepage. Elevated fugacity fractions ( ff > 0.8) reveal a strong thermodynamic migration tendency driving secondary PFAS release into bottom waters via methane-induced “bubble irrigation.” ToxPi prioritization highlights pronounced matrix- and compound-specific vulnerabilities, with 6:2 FTS and perfluorobutanoic acid (PFBA) as primary hazard contributors. These findings identify cold seeps as overlooked hotspots for PFAS source-sink transformation, requiring integration into deep-sea chemical risk frameworks.