Arctic and sub-Arctic marine diatom responses to PFAS exposure: Understanding physiological changes and resilience

Per- and polyfluoroalkyl substances (PFAS) are persistent organic pollutants widely detected across diverse ecosystems. Despite regulatory bans on several PFAS compounds, PFAS remain prevalent in remote areas like the Arctic, raising significant ecological health concerns. This study addresses a critical knowledge gap regarding the effects of PFAS on unicellular primary producers, with a focus on diatom physiology and fitness. Two ecologically important Arctic and sub-Arctic diatom species, Cylindrotheca closterium and Thalassiosira pseudonana, as well as legacy long-chain PFAS, and two emerging PFAS replacements were investigated. Exposures were conducted for 10 days at three concentrations (100 mg/L, 1 mg/L, and 0.9 ng/L). Following the 10 d (short-term) toxicity assessment, one PFAS mixture was exposed for 28 days (long-term) at an environmentally relevant concentration of 0.9 ng/L. Physiological and biochemical responses, including growth, photosynthetic capacity, stress biomarkers, and metabolic changes, were assessed. Results revealed distinct impacts of PFAS on individual PFAS and their mixtures. Perfluorooctane sulfonic acid (PFOS), perfluorooctanoic acid (PFOA), perfluorononanoic acid (PFNA), perfluorododecanoic acid (PFDoA), perfluorotridecanoic acid (PFTrDA), and perfluorotetradecanoic acid (PFTeDA) often exhibited the most detrimental effects on both species relative to controls. PFAS mixtures exhibited synergistic impacts, with increasing effects as the number of PFAS compounds increased. Both diatoms exhibited significant reductions in growth and photochemical efficiency of photosystem II, along with elevated proline and total antioxidant activity, during short-term exposure to PFAS. During the long-term experiment, after the exponential growth phase (after 14 d), growth rates were not significantly different from those of the controls, suggesting potential compensatory responses over time. Despite the mild growth inhibition, enhanced biochemical activity relative to controls indicates sustained metabolic adjustment under prolonged PFAS exposure. These findings emphasize the potential impacts of PFAS, specially in mixtures, on disrupting primary producers in cold marine ecosystems, highlighting the need to assess the cumulative effects of pollutants on foundational Arctic biota.