Effect of carbon chain length and concentration of perfluorinated compounds on polytetrafluoroethylene microplastics transport behavior

Perfluorooctanoic acid (PFOA) and perfluoropentanoic acid (PFPeA), as important components of perfluorinated compounds (PFAS), are not only ecologically hazardous, but also have surfactant properties that can alter the transport behavior of polytetrafluoroethylene (PTFE) in porous media. In this experiment, the effect of PFAS on the transport of PTFE in porous media under different pH, ionic strength (IS) and ion valence states was studied. The results showed that the recovery rate of PTFE decreased gradually with the decrease of pH and the increase of IS and ion valence states. When the above conditions change, the double electron layer on the microplastic surface is compressed, the absolute value of zeta potential decreases, the repulsion between each other decreases, and aggregation and deposition are more likely. In addition, it was found that the recovery rate of PTFE co-transported with long chain PFOA was higher than that of short chain PFPeA. This phenomenon may be caused by the adhesion ability of PFOA with long carbon chain on the surface of PTFE is greater than that of PFPeA with short carbon chain. On the other hand, PFAS with different carbon chain lengths produce different spatial site resistance effects after binding with particles, and the spatial site resistance produced by the long-chain PFOA is larger than that of the short-chain PFPeA, leading to a decrease in particle-to-particle aggregation and a better transport effect. This study will help to understand the effects of PFAS with different carbon chain lengths on the transport of microplastics in porous media, as well as the transport rule of PTFE under different conditions, and provide reference value for the calculation of its flux in soil.