The role of microplastics as carriers of per- and polyfluoroalkyl substances and their fate in the environment

Microplastics (MPs) and perand polyfluoroalkyl substances (PFASs) co-contamination in varying environmental ecosystems is becoming a topic of serious concern due to their widespread presence and persistence in the environment. However, their interaction in the environment has not been understood yet, requiring immediate consideration. This review aims to comprehensively explore the co-sources of PFASs and MPs co-contamination, and their associated interactions in the environment. The co-sources of PFASs and MPs are crucial for proposing appropriate regulations on releasing these contaminants. This study exposes all sources leading to their co- contamination. In addition, several mechanisms, including electrostatic interaction, hydrophobic interaction, hydrogen bonding, and steric effect were the main sorption mechanisms involved in the co-contamination of PFASs and MPs. It was confirmed that the physicochemical properties of the MPs and PFASs, as well as the environmental conditions, play crucial roles in determining the sorption or desorption capacity of PFASs onto MPs. It has been reported that PFASs are more easily adsorbed by biodegradable MPs than conventional MPs. Similarly, the weathering of MPs through the formation of biofilms increases the PFASs sorption capacity by 20-85 % compared to that over virgin MPs. A decreasing trend in PFASs desorption was found in the aged MPs, whereas the desorption rate increased under simulated gastric and intestinal conditions. Moreover, the potential transportation pathways of the sorbed PFASs over MPs in the environment, including atmosphere, soil, and marine ecosystems were proposed. Last but not least, biofilm-covered MPs seem to provide active sites for PFASs biodegradation through the co-metabolism action of bacteria and fungi. Besides, various challenges need to be addressed to understand the mechanisms of the co-contamination of PFASs and MPs, and future research perspectives were provided to further improve the basic understanding and remedial measures for the co- contamination of PFASs and MPs.