Effects of polyamide microplastics on the adsorption of perfluoroalkyl substances in soil

Perfluoroalkyl substances (PFAS) and novel PFAS are continuously detected in soil environments and have attracted increasing attention. The presence of microplastics (MP) in soil systems is of increasing concern worldwide. However, the effects of MP on PFAS adsorption by soil systems remain largely unexplored. In this study, we compared the adsorption behavior of four PFAS on polyamide microplastics (PAMP), polyamide microplastic - soil mixtures (PAMP+soil), and soil to investigate the effects of MP on the adsorption of PFAS in soil. The results show that the four PFAS Perfluorooctanoic acid (PFOA), 6:2 fluorotelomer sulfonic acid (6:2FTSA), Perfluorohexanesulfonate (PFHxS) and Perfluorinated (2-methyl-3-oxohexanoic acid) (GenX) present different adsorption behaviors onto PAMP, PAMP+soil and soil due to their different physicochemical properties. However, similar laws are founded that the adsorption capacity of PAMP, with respect to the four PFAS, is stronger than that of PAMP+soil (20–56 times), followed by that of soil (72–122 times). PAMP amends into soil greatly inhibits the adsorption capacity of PAMP because their surfaces are covered with soil particles or biofilms. The inhibition rate decreases with increasing PAMP dosage. However, the addition of PAMP to soil significantly enhances the adsorption of PFAS compared with that of soil alone. This enhancement indicates that the input of MP into the soil might reduce the mobility of PFAS by improving the adsorption capacity of the soil. Furthermore, the co-culture time of PAMP and soil mixture has a slight impact on adsorption, suggesting that the effect of MP on soil adsorption of PFAS is almost stable. The findings of this study contribute to the understanding of the effects of PAMP in soil on the environmental behavior of PFAS and provide a valuable reference for evaluating the potential risk posed by the co-existence of MP and organic contaminants in soil ecosystems.