What do emerging PFAS tell us that the classic ones did not? Insights from in vitro assays.

Per- and polyfluoroalkyl substances (PFAS) are synthetic chemicals that are recognized for their environmental persistence and potential toxicity. As regulatory pressure increases on legacy PFAS, emerging alternatives are being increasingly used. However, their environmental toxicological profiles remain poorly understood. The present study compares the biochemical effects of legacy (PFOS, PFOA, and PFNA) and emerging (GenX, PFBA, PFBS, and PFHxS) PFAS on the mussel species Mytilus galloprovincialis, using in vitro exposures of digestive gland (DG) and gills (G) tissues. The results highlighted tissue-specific responses, with greater biochemical variability observed in the DG. This was particularly evident under exposure to emerging PFAS, which appeared to induce oxidative stress disturbances and detoxification pathways, as indicated by increased acetylcholinesterase (AChE) and glutathione S-transferases activities and reduced total antioxidant capacity (TAC) levels. In contrast, the G showed a strong inhibition of both AChE and carboxylesterases activities and decreased TAC levels, possibly due to neurotoxic effects and compromised redox homeostasis. These findings suggest that emerging PFAS induce diverse and pronounced effects in the DG, whereas legacy PFAS generally cause less divergent biochemical responses. Further research into intra-group variability, especially among emerging PFAS, is essential for understanding their ecological risks and developing targeted regulatory frameworks.