Cotransport of PFOA with Different Electrically Charged Plastic Particles in Saturated Porous Media

The wide application of industrial and consumer product leads to the ubiquitous presence of PFOA (an anionic surfactant) in natural environments. PFOA could interact with microplastics (one emerging pollutants abundant in environments) and the transport of both PFOA and microplastics thus might be altered. The cotransport behaviors of PFOA with micron-sized plastic particles (MPs) with different surface charge (both negative and positive surface charge) in porous media in both 10 and 50 mM NaCl solutions were investigated in present study. Both types of MPs (negatively charged carboxylate-modified MPs (CMPs) and positively charged amine-modified MPs (AMPs)) could adsorb PFOA onto MPs surfaces which decreased PFOA transport with MPs co-present in suspensions under both solution conditions examined. PFOA had diverse impact on the transport behaviors of CMPs and AMPs. Specifically, PFOA decreased the transport of CMPs, while increased the transport of AMPs when PFOA was copresent in suspensions. The mechanisms driving to the changed transport of two types of MPs induced by PFOA were found to be different. The decreased electrostatic repulsion of CMPs due to the adsorption of PFOA onto CMPs surfaces led to the decreased transport of CMPs when PFOA was copresent. The increased electrostatic repulsion due to the adsorption of PFOA onto AMPs surfaces as well as the steric repulsion induced by suspended PFOA caused the enhanced AMPs transport with PFOA in solutions. The results of this study show that when PFOA and microplastics are copresent in natural environments, their interaction with each other will alter their transport behaviors in porous media, and the alteration is highly correlated with the surface charge of MPs.