Perfluorooctane sulfonate (PFOS) in surface water predicts PFOS concentrations in filets of freshwater fish

Perfluorooctane sulfonate (PFOS), a member of the per- and polyfluoroalkyl substances family, is highly bioaccumulative and remains a persistent public health concern for consumers of wild freshwater fish. However, testing fish tissue for PFOS is time-consuming and costly, and it requires fish mortality. To reduce these costs by furthering the understanding of controls on PFOS bioaccumulation, we analyzed 3,831 paired fish tissue and surface water grab samples collected between 2006 and 2023 from 185 sites in Colorado, Minnesota, and Wisconsin, United States. We found that surface water samples reliably predict PFOS concentrations in fish filets. Species-averaged tissue PFOS scales log-linearly with water PFOS (R2 = 0.49). Adding fish taxonomy modestly improves fit (R2 = 0.69), while fish length, feeding guilds, and habitat preferences contribute little compared with water concentration. Decision tests tied to common fish consumption advisory targets (3.9-200 ng/g) yield surface water thresholds of ∼2.3-26.2 ng/L and strong classification abilities (AUC 0.85-0.97). We posit that surface water PFOS is a practical, defensible proxy for fish PFOS that can accelerate protection while improving efficiency. Regulatory agencies could adopt a tiered framework using surface water PFOS concentrations to triage waterbodies for fish sampling, thus reducing costs, limiting fish mortality, and enabling timely, consistent advisories.