Interactions between Per- and Polyfluoroalkyl Substances (PFAS) at the Water-Air Interface

Area of Science:

• Environmental Chemistry
• Surface Science
• Computational Chemistry

Background:

• Per- and polyfluoroalkyl substances (PFAS) are widespread contaminants in drinking water.
• Standard water treatment methods are often ineffective at removing PFAS.
• PFAS accumulate at water-air interfaces, influencing their environmental behavior and remediation.

Purpose of the Study:

• To investigate the impact of organic loading on PFAS adsorption at water-air interfaces.
• To elucidate the molecular mechanisms governing PFAS accumulation at interfaces.

Main Methods:

• Molecular dynamics simulations were employed.
• Simulations were conducted with varying interfacial densities of PFAS.
• Interactions between PFAS molecules and with other interfacial components were analyzed.

Main Results:

• Adsorbed PFAS form ordered interfacial coatings driven by strong mutual interactions.
• Attractions between perfluoroalkyl chains and electrostatic interactions between head groups are key.
• These interactions can lead to near-cancellation of hydrophobic attraction and Coulomb repulsion.
• PFAS adsorption is sensitive to the composition and density of interfacial coatings.

Conclusions:

• The study explains the paradox of seemingly minimal interactions in adsorption isotherms versus high sensitivity to interfacial conditions.
• Understanding these interfacial interactions is vital for accurate prediction of PFAS fate and transport.
• This knowledge can inform the design of more effective PFAS remediation technologies.