Microplastics, PFAS, and their potential for interaction in the environment

The potential for simultaneous exposure to MPs and certain PFAS is an area of increasing study. The myriad of different types of both MPs and PFAS make predictions of their combined behaviour challenging. Even so, there is evidence that, while sorption of PFAS onto MPs is governed by complex interactions of physicochemical forces, certain PFAS have been shown to adsorb to certain MPs, and thereby affect their fate and transport in the environment.

The nature of these sorption processes depends on both the individual characteristics of the specific PFAS and MP and the surrounding environmental conditions^{3, 4}. Aquatic environments generally serve as the primary medium for PFAS and MP transport and chemical interactions and consequently represent the ecosystem with the greatest potential for combined interactions².

The dominant interaction mechanisms governing PFAS sorption to MPs in aquatic environments may include the following:^{1, 2, 3}

• Hydrophobic interactions: where water repels nonpolar molecules (such as certain PFAS and MPs), forcing them together and causing the surrounding water molecules to group together more tightly.
• Electrostatic interactions: can cause certain PFAS to bind to MPs due to the attractive or repulsive forces acting between electrically charged particles or molecules.
• Pore-filling mechanisms: can cause certain PFAS molecules to occupy micropores and nanopores within MP matrices at the limits of their solubility.

Of these, hydrophobic interactions likely represent the most influential sorption mechanism as most MPs and PFAS are hydrophobic or have hydrophobic portions of their chemical structures. This can cause hydrophobic interactions to become the most dominant force of attraction and ‘overpower’ other MP and PFAS interaction mechanisms^{3, 5}.

Other interactive mechanisms that are either included within the three main ones above or play a smaller role include hydrogen bonding, van der Waals forces, and halogen bonding⁶.

The strength of sorption interactions depends on the characteristics of the specific MPs and PFAS being considered and the surrounding environmental conditions. The main characteristics of MPs that can affect the sorption of substances include size, age, hydrophobicity (the tendency to repel water), and polarisability (how readily molecules can take on an electric charge). Various studies have provided differing results for which polymers have a greater affinity for sorption of certain PFAS, but smaller and older ‘weathered’ MPs have been shown to possess a greater affinity, mainly due to their larger surface-area-to-volume ratio, which increases the number of potential ‘sorption sites’ on the MP⁶.

The main characteristics of PFAS that affect sorption onto MPs include their carbon chain length^{2, 5, 6} as well as their hydrophobicity and polarisability⁷). Short-chain PFAS are generally more likely to interact with MPs through electrostatic sorption, while long-chain PFAS are more likely to interact via hydrophobic sorption^{3, 6}. With hydrophobicity being the most influential interaction mechanism, long-chain PFAS, such as perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS), have been shown to adsorb to the surface of MPs more readily than short-chain PFAS, such as perfluorobutanoic acid (PFBA) and perfluorobutane sulfonate (PFBS)⁸.

The intensity of potential interactions between PFAS and MP is heavily modulated by the surrounding environmental conditions. Of these, salinity, pH, and dissolved organic matter (DOM) are believed to be the most influential^{1, 2}.

Saline conditions found in seawater and hard freshwater² can act as a major catalyst by reducing certain PFAS solubility and may cause ‘squeezing’ certain PFAS molecules onto the plastic surface, whilst pH and DOM often act as regulators, limiting interaction between PFAS and MP; higher pH levels increase electrostatic repulsion between PFAS and MP and organic matter can compete for the same limited space on the plastic.

At potential locations where PFAS and MPs may both be found, such as landfills or land receiving regular biosolid applications (Figure 1), PFAS and MPs may be distinctly present or present as colloidal particles (any substance consisting of particles substantially larger than atoms or ordinary molecules but too small to be visible to the unaided eye) within both the solid material and leachate. Where this is the case, MPs may prevent sorbed PFAS from migrating offsite (in particulate form) in soils with less pore space (more compact); conversely, soils with greater pore space may promote the migration of sorbed PFAS with MPs more easily able to traverse soil pores^{1, 2, 9}.

Contaminated land containing both MPs and PFAS on eroding or low-lying coastlines (such as coastal landfills) may represent greater potential than inland landfills for combined release of MPs and PFAS, as a result of coastal erosion of soils containing both small and large pores.

Given the high solubility and anionic repulsion of certain PFAS from negatively charged soil particles, they are typically highly mobile in aquatic systems, including groundwater and saturated soils².

If this is the case, how can MPs increase the mobility of these already highly mobile PFAS particles in aquatic environments?

When sorbed onto MPs, PFAS mobility becomes tied to the fate of the particle until the PFAS is released. If the MP itself is a ‘smaller’ particle (for example <100 µm with a high buoyancy, such as low-density polyethylene (LDPE), then it can act as a transport vehicle that enables sorbed PFAS to travel longer distances than they would by solute transport alone. This may also be true at slower velocities for smaller MPs with a greater density that can penetrate deeper into groundwater systems and potentially settle on less permeable soils near the bottom of the groundwater system in question.

From a transport and fate perspective, sorbed PFAS are then subject to the suspension ability of the MP, which in turn, can be subject to biofouling, fragmentation, or aggregation and flocculation that can alter the fate of the MP by causing it to sink or float.

In summary, MPs containing sorbed PFAS may be transported long distances by currents or settle in sediments within aquatic systems, creating combined MP-PFAS sinks, depending on the MP they are sorbed to and the subsequent environmental conditions to which they are exposed.

It is apparent that MPs with sorbed contaminants such as PFAS may pose risk assessment and land management challenges.

On higher risk sites, where it is likely that high concentrations of smaller MPs (for example < 100 µm) are present alongside certain PFAS, potential combined transport and toxicity consequences should be examined and accounted for within management strategies.

Aquatic transport and fate characteristics for MPs (such as colloidal, sediment, and solute transport modelling, where appropriate) may provide insight into potential sinks for MPs with sorbed contaminants such as PFAS¹⁰. Figure 2 summarises some of the major pathways and sinks for MPs¹¹.

It is important to recognise that the ability for MPs to transport sorbed contaminants goes beyond PFAS alone. Industrial facilities that may be releasing MPs in wastewater are likely to come under increasing scrutiny from regulatory authorities in the future regarding their releases.

In Spring 2026, MPs were added to both the European Union’s quality standards and the US Environmental Protection Agency’s watch list. More research and monitoring is needed to help identify potential MP combined contamination sources and sinks, and to standardise specific management solutions that can be used by industry, landowners, consultants, and regulators to deal with this issue.

Ramboll offers a comprehensive suite of services to industrial and manufacturing clients (e.g. textiles, plastics manufacturing, coatings/chemicals, personal care product companies), regulatory authorities, water and wastewater companies, contaminated land owners/developers, waste and resource management clients (e.g. landfill operators, waste management companies, recycling firms), other environmental advisory/consultancy companies, and academics (for future research on this topic).

Our expertise includes:

• Land contamination risk assessment and management
• Environmental fate and transport modelling (including hydrological and hydrogeological studies/assessments)
• Monitoring and site investigation
• Environmental impact assessment
• Remediation strategy support
• Regulatory and compliance advisory (including research and advisory on emerging contaminants)
• Wastewater and industrial discharge advisory

About the author: Dr Ben Stride is a Senior Environmental Consultant with Ramboll. Ben’s work mainly involves emerging contaminants, land contamination, and hydrogeology. He studied the transport and fate of microplastics as part of his doctoral research at the University of Warwick.

^{1 Brenckman, C. M., Borgaonkar, A. D., Pennock, W. H., III, & Meegoda, J. N. (2026). Combined Environmental Impacts and Toxicological Interactions of Per- and Polyfluoroalkyl Substances (PFAS) and Microplastics (MPs). Environments, 13(1), 38. https://doi.org/10.3390/environments13010038}

^{2 Wang, P., Shi, Y. Z., & Guan, Q. (2025). The Microplastic-PFAS Nexus: From Co-Occurrence to Combined Toxicity in Aquatic Environments. Toxics, 13(12), 1041. https://doi.org/10.3390/toxics13121041}

^{3 Yu, F., Wu, J., Wang, H., Bao, Y., et al. (2024) Interaction of microplastics with perfluoroalkyl and polyfluoroalkyl substances in water: A review of the fate, mechanisms and toxicity, Science of The Total Environment, 948. https://doi.org/10.1016/j.scitotenv.2024.175000}

^{4 Prajapati, A., Narayan Vaidya, A. & Kumar, A.R. Microplastic properties and their interaction with hydrophobic organic contaminants: a review. (2022). Environ Science and Pollution Research, 29, 49490–49512. https://doi.org/10.1007/s11356-022-20723-y}

^{5 Islam, S., Kekre, K, M., Shah, T, A., Tsai, P-C. et al. (2025). Unraveling the complexities of microplastics and PFAS synergy to foster sustainable environmental remediation and ecosystem protection: A critical review with novel insights, Journal of Hazardous Materials Advances, 17. https://doi.org/10.1016/j.hazadv.2025.100621}

^{6 Mejías, C., Martín, J., Santos, J, L., Aparicio, I. et al. Adsorption of perfluoroalkyl substances on polyamide microplastics: Effect of sorbent and influence of environmental factors, Environmental Research, 216. https://doi.org/10.1016/j.envres.2022.114834.}

^{7 Leung, S, C, E., Wanninayake, D., Chen, D., Nguyen, N-T et al. (2023). Physicochemical properties and interactions of perfluoroalkyl substances (PFAS) - Challenges and opportunities in sensing and remediation, Science of The Total Environment, 905. https://doi.org/10.1016/j.scitotenv.2023.166764}

^{8 Parashar, N., Mahanty, B., Hait, S. (2023). Microplastics as carriers of per- and polyfluoroalkyl substances (PFAS) in aquatic environment: interactions and ecotoxicological effects. Water Emerging Contaminants. Nanoplastics, 2, 15. http://dx.doi.org/10.20517/wecn.2023.25}

^{9 Guo, J-J., Huang, X-P., Xiang, L., Wang, Y-Z. et al. (2020). Source, migration and toxicology of microplastics in soil. Environment International, 137. https://doi.org/10.1016/j.envint.2019.105263}

^{10 Stride, B., Abolfathi, S., Bending, G. D., Pearson, J. (2025). Hyporheic exchange processes of pore-scale microplastics. Science of the Total Environment, 982. https://doi.org/10.1016/j.scitotenv.2025.179573}

^{11 Stride, B. (2024). Doctoral thesis on ‘Quantifying microplastic transport in freshwater and wastewater flow domains’. University of Warwick. http://webcat.warwick.ac.uk/record=b4091156}