Mineral-biofilm interaction controls trophic transfer of PFAS along a biofilm-snail food chain

Natural biofilms developing on mineral substrates at the soil-water interface in freshwater ecosystems are important sinks of per- and polyfluoroalkyl substances (PFAS). However, the role of mineral-biofilm interactions in regulating their trophic transfer remains poorly understood. This study investigates how Fe 2 O 3 is associated with changes in the distribution of PFAS within the biofilm matrix in a carbon chain length-dependent manner, which may further affect PFAS trophic transfer to snails. Fe 2 O 3 preferentially localizes within the tightly bound extracellular polymeric substances (TB-EPS) layer, coincides with stimulated EPS production and altering PFAS partitioning within biofilms, and correlates with the redistribution of long-chain PFAS (e.g., PFNA) from loosely bound to tightly bound EPS fractions. In addition, Fe 2 O 3 alleviates PFNA-induced toxicity and reshapes microbial community composition, increasing the relative abundance of Cyanobacteria and improving biofilm nutritional quality, which in turn may enhance snail grazing. Consequently, Fe 2 O 3 is associated with a significant increase in the trophic transfer factor of PFNA from biofilms to snails (approximately 35%), while showing negligible effects on short-chain PFAS. Overall, these results suggest that Fe 2 O 3 may enhance the trophic transfer of long-chain PFAS through combined effects on contaminant partitioning and biofilm quality, highlighting the important role of mineral-associated biofilms in PFAS bioaccumulation and providing new insights for ecological risk assessment in freshwater ecosystems.