Environmental Interfaces and Emerging Contaminants: PFAS Interactions with Microplastics and Dissolved Organic Matter

Abstract

Per- and polyfluoroalkyl substances (PFAS) are a diverse class of over 4,000 synthetic chemicals widely used in industrial and consumer products, including non-stick cookware, food packaging, textiles, and aqueous film-forming foams (AFFFs). Their unique amphiphilic structure, consisting of a hydrophobic fluorinated carbon chain and a hydrophilic functional head group, imparts exceptional chemical stability and environmental persistence. As a result, PFAS are frequently detected in environmental systems where they interact with co-occurring materials such as microplastics (MPs) and dissolved organic matter (DOM). Microplastics are ubiquitous in terrestrial and aquatic environments and exist as either pristine particles or weathered forms resulting from abiotic and biotic processes. In this study, polyethylene microbeads were incubated in an aquatic mesocosm for 15 months to simulate environmental weathering. Compared to pristine MPs, weathered MPs exhibited significant physicochemical alterations, including increased surface oxidation and heterogeneity. Fourier-transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) analyses revealed the formation of oxygen-containing functional groups (e.g., carbonyl and carboxyl), while scanning electron microscopy (SEM) showed surface cracks, divots, and mineral attachments. Adsorption–desorption experiments demonstrated that weathered MPs enhanced the adsorption of long-chain PFAS relative to pristine MPs and MP-free sediments, whereas short-chain PFAS exhibited negligible adsorption, likely due to their greater affinity for the aqueous phase.

In agricultural systems, PFAS inputs are often associated with the land application of organic amendments such as biosolids and manure, which introduce both PFAS and DOM. While DOM is known to influence PFAS partitioning, the mechanisms governing this process remain poorly constrained. DOM can facilitate PFAS adsorption through bridging interactions with soil colloids or through direct complexation, but may also compete for sorption sites. Using fluorescence excitation–emission matrix (EEM) spectroscopy, changes in DOM fluorophore intensity were evaluated in response to PFAS exposure. Results indicate that PFAS–DOM interactions are highly dependent on DOM composition and environmental conditions. Protein-like fluorophores exhibited an inverse relationship between humification index (HIX) and relative fluorophore intensity (F/F₀), suggesting fluorophore enhancement through restricted molecular motion and reduced solvent-mediated quenching. Collectively, these findings demonstrate that PFAS behavior is strongly influenced by interactions with environmental interfaces, including weathered microplastics and heterogeneous DOM. These interactions can significantly alter PFAS adsorption, mobility, and environmental fate, underscoring the need to consider complex multiphase systems when predicting PFAS transport in natural environments.