Climate-Induced Thermal and Hypoxic Stress Exacerbate the Chronic Ecological Risks of Legacy PFAS in Freshwater...

Freshwater ecosystems are increasingly exposed to climate-driven thermal and hypoxic stress, which can modulate the aquatic sensitivity to chemical contaminants and thus undermine traditional static water quality criteria. Here, we used a multistressor potentially affected fraction framework integrating stressor-specific species sensitivity distributions to quantify the ecological risks of perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS) across thermal and hypoxic gradients. Under a scenario with a thermal effect margin of 2 °C or a hypoxic effect margin of 2.8 mg/L, 5% hazardous concentrations declined to approximately one-tenth of baseline levels, from 13 to 2 μg/L for PFOA and from 0.6 to 0.1 μg/L for PFOS. Accordingly, risks in Chinese surface waters increased markedly, with risk quotients exceeding 10 at several sites in the lower Yangtze and Yellow Rivers. Joint probability curve analysis showed consistent trends, with even modest and environmentally realistic stressor shifts increasing risk probability up to 8-fold. Risk amplification was primarily driven by mild-to-moderate ecological effects. Additionally, combined thermal-hypoxic stress produced scenario-dependent responses with heterogeneous dominant drivers across the temperature-dissolved oxygen space. This study demonstrates that climate-driven stressors can reshape contaminant risk landscapes, supporting a shift from single- to multistressor ecological risk frameworks.