Comparative Hepatotoxicity Assessment of PFOS and Its Alternative 6:2 FTSA in Adult Female Zebrafish

As an alternative to perfluorooctane sulfonate (PFOS), 6:2 fluorotelomer sulfonic acid (6:2 FTSA) has been increasingly produced and detected in aquatic environments, yet its toxicological effects in fish remain incompletely characterized. In this study, adult female zebrafish were exposed for 30 days to solvent control (CK), 50 μg/L PFOS (P50), 50 μg/L 6:2 FTSA (F50), and 500 μg/L 6:2 FTSA (F500), respectively. Histopathological analysis revealed that both compounds induced hepatic injury, with the most severe damage observed in the F500 group. Hepatic transcriptomic analysis identified 645, 191, and 85 differentially expressed genes (DEGs) in the P50, F50, and F500 groups versus CK, respectively. Functional enrichment analysis further demonstrated distinct toxic profiles: PFOS at 50 μg/L primarily disrupted pathways related to the cell cycle, DNA replication, and reproduction. In contrast, 50 μg/L 6:2 FTSA predominantly activated PPAR-mediated lipid metabolism pathways, consistent with a "metabolic toxicity" phenotype. Notably, at 500 μg/L, 6:2 FTSA induced the most severe injury accompanied by a distinct transcriptomic signature-characterized by fewer DEGs but a pronounced enrichment of endoplasmic reticulum stress pathways-suggestive of a shift from metabolic perturbation to overwhelming cellular stress. Biochemical analysis confirmed a significant increase in malondialdehyde (MDA) only in the F50 group, supporting oxidative stress-mediated metabolic toxicity. Collectively, these findings demonstrate that 6:2 FTSA is not a safe alternative to PFOS but exhibits a dose-dependent and multifaceted toxicological profile, with high-dose effects indicative of acute cellular stress. This study underscores the need for case-specific, dose-range inclusive risk assessment of emerging PFAS alternatives.