Emergent pollutants, escalating pressures: GenX effects on mussels in a changing environment.

Per- and polyfluoroalkyl substances (PFAS) are persistent pollutants with rising concern due to their stability and toxicity. The production of novel PFAS with shorter carbon chains in the environment raises concerns related to their stability and their potential toxicity in organisms. This study examines the effects of hexafluoropropylene oxide dimer acid ammonium (HFPO-DA, or GenX) on the marine mussel Mytilus galloprovincialis under different salinity conditions. Mussels were exposed to environmentally relevant HFPO-DA concentrations, and multiple biomarkers were assessed: these include oxidative stress responses and damages, as well as neurotoxicity and histological damages. Results show that salinity strongly modulates toxicity: hyposaline conditions activated robust antioxidant defenses and increased respiration, while intermediate and high salinities led to greater metabolic disruption and cellular damage. At the highest concentration of HFPO-DA at intermediate salinities, mussels favored non-enzymatic antioxidant responses over enzymatic activity. These findings reveal a complex interplay between salinity and PFAS toxicity and underscore the need to integrate environmental variability into ecotoxicological risk assessments. Therefore, both climate change and PFAS pollution in estuarine ecosystems require urgent, context-sensitive mitigation strategies.