Molecular-Scale Insights into the Interactions between Perfluoroalkyl Substances and Polyethylene

Area of Science:

• Environmental Chemistry
• Materials Science
• Computational Chemistry

Background:

• Microplastics (MPs) and per- and polyfluoroalkyl substances (PFAS) are persistent environmental contaminants.
• Their co-occurrence raises concerns about synergistic effects and enhanced environmental persistence.

Purpose of the Study:

• To investigate the adsorption interactions between polyethylene (PE) microplastics and two common PFAS: perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS).
• To elucidate the molecular mechanisms governing PFAS adsorption onto PE using computational simulations.

Main Methods:

• Molecular dynamics (MD) simulations were employed to model the adsorption of PFOA and PFOS onto semicrystalline and crystalline polyethylene (PE).
• The potential of mean force (PMF) was calculated to quantify the free energy of adsorption.
• Molecular orientation of PFAS at the PE-water interface was analyzed.

Main Results:

• Both PFOA and PFOS adsorb to PE, with PFOS exhibiting stronger binding affinity than PFOA, attributed to its larger, more hydrophobic sulfonate group.
• No significant difference in adsorption energy was observed between semicrystalline and crystalline PE morphologies.
• PFAS molecular orientation at the PE-water interface is influenced by PE structure and local energy barriers, with notable orientation changes for PFOS.

Conclusions:

• Microplastics, specifically PE, can act as environmental reservoirs for PFAS, potentially increasing their persistence and mobility.
• The adsorption affinity and orientation of PFAS on MPs are governed by both polymer morphology and the specific chemical characteristics of the PFAS functional group.
• Findings provide molecular-level insights into the environmental fate and transport of co-occurring MPs and PFAS contaminants.