Combined effect of PFOS and PFOA on phytoplankton interactions and overall community health

Per- and polyfluoroalkyl substances (PFAS), particularly mixtures of perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS), pose significant ecological risks to freshwater phytoplankton communities due to their persistence and potential toxicity. Previous studies have largely overlooked community-level effects of environmentally relevant concentrations. This study examined the impacts of PFOA/PFOS mixtures (10 ng L−1, 10 μg L−1, and 10 mg L−1) on phytoplankton over a four-week mesocosm experiment. The results revealed concentration-dependent responses over time, with low concentration (10 ng L−1) initially stimulating phytoplankton biomass, whereas higher exposures (10 μg L−1 and 10 mg L−1) significantly inhibited growth and altered biochemical composition, notably increasing total protein while decreasing carbohydrate content. The elevated activities of glutathione S-transferase and peroxidase confirmed oxidative stress across all treatments. Network analysis demonstrated progressive disruption of interspecies interactions with increasing PFAS concentrations, culminating in complete loss of some interactions at the highest exposures (10 μg L−1 and 10 mg L−1). This community restructuring favored dominance by stress-tolerant species, such as Microcystis aeruginosa, potentially destabilizing aquatic ecosystems. These findings highlight the need to re-evaluate the ecological risk assessments for PFAS mixtures, particularly their capacity to reshape phytoplankton communities through physiological and interactive mechanisms in freshwater environments.